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Different approaches have been used to identify fishery stock status when only biomass and catch data are available. However, the performance of the approaches may be affected by the uncertainties derived from different sources (e.g., model misspecification, stock productivity changing, observation error). Here, we propose that the observed biomass associated with the highest calculated surplus production can be used as an indicator ([B.sub.highest_S]) to identify stock status. We develop a management procedure (MP) atop a widely used method (i.e., Gcontrol) by incorporating [B.sub.highest_S] in the harvest control rule. Two simulations are conducted to compare the stock status identification approaches and corresponding MPs. Using [B.sub.highest_S] to identify stock status performs better than surplus production modeling approaches in simulated regime shift scenarios. Compared with the old version of Gcontrol, incorporating [B.sub.highest_S] or estimated [B.sub.MSY] in the harvest control rule provides more stable and higher yields. This study contributes to the development and evaluation of indicator-based stock status identification approaches and MPs that only require biomass and catch data. Differentes approches ont ete utilisees pour determiner l'etat de stocks de peche quand seules des donnees sur la biomasse et les prises sont disponibles. Des incertitudes issues de differentes sources (p. ex. parametrisation inadequate de modeles, variation de la productivite du stock, erreur d'observation) peuvent toutefois avoir une incidence sur la performance de ces approches. Nous proposons que la biomasse observee associee a la plus forte production excedentaire calculee peut etre utilisee comme indicateur ([B.sub.highest_S]) pour determiner l'etat d'un stock. Nous superposons une procedure de gestion (PG) a une methode largement utilisee (c.-a-d., Gcontrol) en incorporant [B.sub.highest_S] dans la regle de controle des prises. Deux simulations sont effectuees afin de comparer les approches de determination de l'etat du stock et les PG correspondantes. L'utilisation du [B.sub.highest_S] pour determiner l'etat du stock donne de meilleurs resultats que des approches de modelisation de la production excedentaire dans des scenarios de changement de regime simule. Comparativement a l'ancienne version de Gcontrol, l'incorporation du [B.sub.highest_S] ou du [B.sub.MSY] estime dans la regle de controle des prises produit des rendements plus stables et eleves. L'etude constitue une contribution a l'elaboration et l'evaluation d'approches de determination de l'etat des stocks et de PG basees sur des indicateurs qui ne necessitent que des donnees sur la biomasse et les prises. [Traduit par la Redaction], 1. Introduction The majority of commercially exploited fish stocks lack sufficient data for sophisticated age- or size-structured assessment models. This incapacity poses a major challenge for the sustainable management of [...]

Accurate age data are essential for reliable fish stock assessment. Yet many stocks suffer from inconsistencies in age interpretation. A new approach to obtain age makes use of the chemical composition of otoliths. This study validates the periodicity of recurrent patterns in [sup.25]Mg, [sup.31]P, [sup.34]K, [sup.55]Mn, [sup.63]Cu, [sup.64]Zn, [sup.66]Zn, [sup.85]Rb, [sup.88]Sr, [sup.138]Ba, and [sup.208]Pb in Baltic cod (Gadus morhua) otoliths from tag-recapture and known-age samples. Otolith P concentrations showed the highest consistency in seasonality over the years, with minima co-occurring with otolith winter zones in the known-age otoliths and in late winter--early spring when water temperatures are coldest in tagged cod. The timing of minima differs between stocks, occurring around February in western Baltic cod and 1 month later in eastern Baltic cod; seasonal maxima are also stock-specific, occurring in August and October, respectively. The amplitude in P is larger in faster-growing western compared with eastern Baltic cod. Seasonal patterns with minima in winter--late spring were also evident in Mg and Mn, but less consistent over time and fish size than P. Chronological patterns in P, and to a lesser extent Mg and Mn, may have the potential to supplement traditional age estimation or to guide the visual identification of translucent and opaque otolith patterns used in traditional age estimation. Resume : Si des donnees exactes sur l'age revetent une importance fondamentale pour l'evaluation fiable des stocks de poissons, l'interpretation des ages pour de nombreux stocks est minee par des incoherences. Une nouvelle approche d'estimation des ages repose sur la composition chimique des otolites. La presente etude valide la periodicite de motifs recurrents des concentrations de [sup.25]Mg, [sup.31]P, [sup.34]K, [sup.55]Mn, [sup.63]Cu, [sup.64]Zn, [sup.66]Zn, [sup.85]Rb, [sup.88]Sr, [sup.138]Ba et [sup.208]Pb dans des otolites de morue (Gadus morhua) de la mer Baltique tires d'echantillons de marquage-recapture et d'ages connus. Les concentrations de P des otolites montrent la plus grande coherence sur le plan de la saisonnalite au fil des annees, des minimums concordant avec les zones hivernales dans les otolites d'age connu et avec la fin de l'hiver ou le debut du printemps, quand les temperatures de l'eau sont les plus froides, dans les morues etiquetees. Le moment des minimums differe entre les stocks, se produisant vers fevrier dans les morues de l'ouest de la Baltique et 1 mois plus tard dans les morues de l'est de la Baltique; les maximums saisonniers varient aussi selon le stock, se produisant en aout et octobre, respectivement. L'amplitude des concentrations de P est plus grande dans les morues a croissance plus rapide de l'ouest que dans celles de l'est de la Baltique. Des motifs saisonniers du Mg et du Mn presentant des minimums en hiver--a la fin du printemps sont aussi evidents, bien que moins coherents dans le temps et selon la la taille des poissons que ceux du P. Les motifs temporels du P et, dans une moindre mesure, du Mg et du Mn pourraient ameliorer les estimations de l'age par l'approche traditionnelle ou guider l'identification visuelle des motifs de zones translucides et opaques d'otolites utilises pour estimer l'age de maniere traditionnelle. [Traduit par la Redaction], Introduction Age information is one of the basic input variables in modern stock assessments, from which parameters such as growth, maturation patterns, and productivity are estimated. Accurate age estimates are [...]

An ichthyofauna review of literature prior to 2008 on the Withlacoochee River basin in south-central Georgia, USA, indicated that the fish fauna was underrepresented compared to other rivers, such as the Suwannee River basin in Florida of which the Withlacoochee River is a tributary. A survey would provide the state of Georgia potentially valuable additional information on the fish fauna within the basin. A 45-site survey within the eastern portion of the Withlacoochee River basin was conducted from 2008 to 2010 employing seines, gill nets, fish traps, trotlines, and creel surveys. Surveys yielded 51 fish species of which three, the Alabama Shad (Alosa alabamae), the Suwannee Bass (Micropterus notius), and the Metallic Shiner (Pteronotropis metallicus), are species of concern in Georgia with the Alabama Shad and the Suwannee Bass listed on the International Union for Conservation of Nature threatened species red list. Three species not previously recorded in the Withlacoochee River basin, the Brown Darter (Etheostoma edwini), the Gulf Coast Pygmy Sunfish (Elassoma gilberti), and the Hogchoker (Trinectes maculatus) were collected. The first known sympatric populations of the Everglades Pygmy Sunfish (Elassoma evergladei) and the Gulf Coast Pygmy Sunfish were found at one location. Invasive species found in the drainage basin were the Green Sunfish (Lepomis cyanellus) and two specimens of Pacu (Piaractus brachypomus). A Friedman cumulative comparison indicated that fish assemblage distribution patterns, as related the stream orders of the river and the potential impact of a sinkhole plain in the river, did not vary from other published surveys on distribution patterns. However, a cluster analysis comparing species composition by collection site showed some similarities among river orders. Keywords: fish survey, species richness, distribution patterns, assemblage structures, species of concern, INTRODUCTION The objectives of this research were to conduct a detailed ichthyofaunal survey of the eastern portion of the Withlacoochee River basin from its headwaters to the Georgia/Florida state line [...]

An ichthyofauna review of literature prior to 2008 on the Withlacoochee River basin in south-central Georgia, USA, indicated that the fish fauna was underrepresented compared to other rivers, such as the Suwannee River basin in Florida of which the Withlacoochee River is a tributary. A survey would provide the state of Georgia potentially valuable additional information on the fish fauna within the basin. A 45-site survey within the eastern portion of the Withlacoochee River basin was conducted from 2008 to 2010 employing seines, gill nets, fish traps, trotlines, and creel surveys. Surveys yielded 51 fish species of which three, the Alabama Shad (Alosa alabamae), the Suwannee Bass (Micropterus notius), and the Metallic Shiner (Pteronotropis metallicus), are species of concern in Georgia with the Alabama Shad and the Suwannee Bass listed on the International Union for Conservation of Nature threatened species red list. Three species not previously recorded in the Withlacoochee River basin, the Brown Darter (Etheostoma edwini), the Gulf Coast Pygmy Sunfish (Elassoma gilberti), and the Hogchoker (Trinectes maculatus) were collected. The first known sympatric populations of the Everglades Pygmy Sunfish (Elassoma evergladei) and the Gulf Coast Pygmy Sunfish were found at one location. Invasive species found in the drainage basin were the Green Sunfish (Lepomis cyanellus) and two specimens of Pacu (Piaractus brachypomus). A Friedman cumulative comparison indicated that fish assemblage distribution patterns, as related the stream orders of the river and the potential impact of a sinkhole plain in the river, did not vary from other published surveys on distribution patterns. However, a cluster analysis comparing species composition by collection site showed some similarities among river orders. Keywords: fish survey, species richness, distribution patterns, assemblage structures, species of concern, INTRODUCTION The objectives of this research were to conduct a detailed ichthyofaunal survey of the eastern portion of the Withlacoochee River basin from its headwaters to the Georgia/Florida state line [...]

More than half of the fish biomass of coastal rocky reefs depends on zooplankton; however, the trophic basis of estuarine fish assemblages remains unknown. We quantified the trophic basis (i.e. basal energy sources) of fish community biomass inhabiting three habitat types (seagrass, natural reef and artificial reef) in two estuaries, compared with two coastal rocky reef sites. Fish assemblages were surveyed with Baited Remote Underwater Video (BRUVs) and the species abundance, richness and biomass of fish were classified into nine functional feeding groups (6 teleost and 3 elasmobranch). Comparable metrics for coastal fish assemblages were obtained from published surveys using BRUVs. Using the functional feeding group biomass and the group-specific diet composition, the breakdown of energy sources was calculated using a food web analysis. Estuarine reef habitats had different species and different functional feeding group composition than seagrass habitat. The majority of fish biomass in the seagrass habitat was supported by detritus (51% in Botany Bay) or macrophytes (58% in Lake Macquarie). In contrast, zooplankton supported most fish biomass (45-59%) at the coastal reef locations, and in reef habitat in one estuary (35-43%), but not the other estuary (33-34%). Trophic pathways which support fish assemblages, are key in identifying mitigation measures which can help conserve these populations with growing urbanisation of estuaries and coasts., Author(s): Belinda K. Goddard [sup.1] , Alistair Becker [sup.2] , David Harasti [sup.2] , James A. Smith [sup.1] [sup.3] , Roshni C. Subramaniam [sup.4] , Iain M. Suthers [sup.1] [sup.4] [...]

Abstract--Migratory behavior affects growth, survival, and fitness of individual fish, the dynamics and resilience of populations, and the ecosystems that fish occupy. Many salmonids are anadromous but individuals vary in [...]

Mesopelagic fishes are important consumers of zooplankton and are the prey of oceanic predators. Some mesopelagic fishes (e.g., Myctophidae) undertake a diel vertical migration where they ascend to the near-surface waters during the night to feed and descend into the depths during the day to avoid predators. Other mesopelagic fishes (e.g., Sternoptyx) remain at depth throughout the day. Although fishes of different depths eat different prey items, vertical migration likely leads to overlap in species distributions and diet, potentially linking trophically transmitted surface and deep-pelagic parasite communities. The study of gut contents and parasites can yield insights into the trophic dynamics occurring within these assemblages. We examined the diet and parasite assemblages of 18 mesopelagic fish species in the Gulf of Mexico. We identified six different feeding guilds within this assemblage based on gut contents: copepods, copepods/mesozooplankton, copepods/ostracods, gelatinous zooplankton, generalist mesozooplankton, and upper-trophic level items such as fish. Although parasite abundances were generally low, mesopelagic fishes hosted a diverse assemblage of parasites, including larval and adult digeneans, larval cestodes, larval nematodes, and larval acanthocephalans. The parasite assemblages differed significantly among host feeding guilds. Large, vertically migrating fishes that predate upon fish and squid communities had a greater likelihood of having one or more parasites compared to the other fishes examined. Results from this study suggest that upper-trophic level mesopelagic fishes are more regularly involved in the life cycle of parasites in the Gulf of Mexico than zooplanktivorous fishes., Author(s): Matthew S. Woodstock [sup.1] , Christopher A. Blanar [sup.2] , Tracey T. Sutton [sup.1] Author Affiliations: (1) grid.261241.2, 0000 0001 2168 8324, Department of Marine and Environmental Sciences, Halmos [...]

Fish assemblage structure has changed dramatically in the Western Basin of Lake Erie since Trautman's revision of the Fishes of Ohio. Fish surveys near the Bass Islands and adjacent mainland tributaries documented fish faunal distributional patterns during the last three decades. Collections (n = 1942 sites) from 1980-2015 indicate 120 extant fish species and 19 extirpated species from the Bass Islands and nearby tributaries to the Western Basin. Extirpation of Polyodon spatula, Alosa sapidissima, Moxostoma lacerum, and Sander glacum occurred; however, Acipenser sapidissima and members of genus Oncorhynchus were introduced but unable to naturalize. Recent collection of rare species included A. fulvescens in Schoolhouse Bay near Middle Bass Island in May 2012; Umbra limi populations on Middle Bass Island and Kelley's Island; and Lepisosteus oculatus populations along the southeastern shoreline of North Bass Island are stable in Lake Erie despite cultural eutrophication. The current Western Basin fish assemblage includes 101 native, 12 nonindigenous, and seven alien fish species. Fourteen native species have been extirpated from the Western Basin of Lake Erie, while six nonindigenous species have not naturalized and have been extirpated. Introduced nonindigenous and alien species are responsible for increased species richness including Neogobius melanostomus, Proterorhinus semilunaris, Salmo trutta, Carassius auratus, Cyprinus carpio, Ctenopharyngodon idella and three records for Hypophthalmichthys nobilis since 1995. Hypophthalmichthys molitrix has never been collected but eDNA testing has indicated its presence. Neither H. nobilis or H. molitrix are considered established in Lake Erie, while Ctenopharyngodon idella may be reproducing within the basin. Brief comments on distribution, relative abundance, and status are provided for each species. Date of Publication: September 2016, INTRODUCTION Many factors have contributed to impacts on Great Lakes fishes, including cultural eutrophication, contamination, and the introduction of nonindigenous and alien species that has contributed to the extinction ofnumerous [...]

Abstract.--It is rare to find evidence of top predators recovering after being negatively affected by overfishing. However, recent findings suggest a nascent return of the critically endangered giant sea bass [...]

The great 'northern' cod (Gadus morhua) stock, formerly among the world's largest and the icon for depletion and supposed nonrecovery of marine fishes, is making a major comeback after nearly two decades of attrition and fishery moratorium. Using acoustic-trawl surveys of the main prespawning and spawning components of the stock, we show that biomass has increased from tens of thousands of tonnes to >200 thousand tonnes within the last decade. The increase was signalled by massive schooling behaviour in late winter first observed in 2008 in the southern range of the stock (Bonavista Corridor) after an absence for 15 years, perhaps spurred by immigration. Increases in size composition and fish condition and apparent declines in mortality followed, leading to growth rates approaching 30% per annum. In the spring of 2015, large increases in cod abundance and size composition were observed for the first time since the moratorium in the more northerly spawning groups of this stock complex. The cod rebound has paralleled increases in the abundance of capelin (Mallotus villosus), whose abundance declined rapidly in the cold early 1990s but has recently increased during a period of warm ocean temperatures. With continued growth in the capelin stock and frugal management (low fishing mortality), this stock could rebuild, perhaps within less than a decade, to historical levels of sustainable yield. More generally, if this stock can recover, the potential exists for recovery of many other depleted stocks worldwide. Le grand stock de morues (Gadus morhua) du Nord, qui figurait parmi les plus importants du monde et constitue l'exemple type de l'effondrement et du non-retablissement presume de poissons marins, fait un grand retour apres presque deux decennies d'attrition et de moratoire sur la peche. A partir de releves acoustiques et au chalut des principaux composants pre-reproducteurs et reproducteurs du stock, nous demontrons que la biomasse a augmente de quelques dizaines de milliers de tonnes a >200 000 tonnes durant la derniere decennie. Cette augmentation a ete signalee par le comportement de rassemblement massif en bancs a la fin de l'hiver, d'abord observe en 2008 dans la partie sud de l'aire de repartition du stock (corridor de Bonavista) apres une absence de 15 ans, qui a peut-etre ete favorise par l'immigration. Des augmentations de la taille et de l'embonpoint des poissons et des diminutions apparentes de la mortalite ont suivi, menant a des taux de croissance annuels approchant les 30 %. Au printemps de 2015, de fortes augmentations de l'abondance et de la taille des morues ont ete observees pour la premiere fois depuis le moratoire dans les groupes reproducteurs plus septentrionaux de ce complexe de stocks. Ce rebond de la morue a accompagne des augmentations de l'abondance du capelan (Mallotus villosus), qui avait diminue rapidement durant la periode froide du debut des annees 1990, mais qui a recemment augmente pendant une periode de temperatures oceaniques plus chaudes. La croissance continue du stock de capelans et une gestion frugale (faible mortalite par peche) pourraient permettre a ce stock de revenir, peut-etre en moins d'une decennie, a ses niveaux de rendement equilibre passes. Plus generalement, si ce stock peut se retablir, cela indique que le retablissement de nombreux autres stocks decimes a l'echelle mondiale est egalement possible. [Traduit par la Redaction], Introduction Many fish stocks worldwide have been overexploited to the point of commercial extinction (FAO 2012), with predictions of the decline or elimination of all major marine fisheries (Worm et [...]

Abstract: Here we report on two new reef fish species from the remote and isolated Easter Island--the striped boarfish Evistias acutirostris and the ornate butterflyfish Chaetodon ornatissimus were observed during [...]

Abstract--A stock assessment incorporating sensitivity in biological parameters and potential fishery management strategies for wahoo (Acanthocybium solandri) in the southwest Pacific Ocean was undertaken to assess the stock status of [...]

Occupancy modeling is well suited to quantitative assessment of bull trout (Salvelinus confluentus) distribution at multiple scales. We used models to estimate occupancy of juvenile bull trout (≤ 150 mm fork length) in a west-central Alberta watershed. Based on a backpack electrofishing survey of 92 sites, we assessed the relative importance of stream habitat characteristics on detection probability (p) and potential for false absences to bias occupancy estimates. Median distance to first bull trout detection was 16 m (range 0-289 m). Models including ambient water conductivity as a covariate of detection probability were most supported with an 85 µS x [cm.sup.-1] increase resulting in over a tenfold increase in detection. Conditional detection probability using backpack electrofishing gear approached 95% in the first 200 m of effort in streams with a conductivity around 200 µS x [cm.sup.-1]. The potential for false absences in our study area was relatively low. Modeled site ([??] = 0.53; SE = 0.13) and patch-scale ([??] = 0.47; SE = 0.12) occupancy closely corresponded to naive (i.e., assuming p = 1) estimates (0.47 and 0.43, respectively). Our results highlight the potential efficiencies of an occupancy modeling approach when assessing fish distribution, but careful consideration of model assumptions is necessary. La modelisation de l'occupation se prete bien a l'evaluation quantitative de la repartition des ombles a tete plate (Salvelinus confluentus) a differentes echelles. Nous avons utilise des modeles pour estimer l'occupation des ombles a tete plate juveniles (longueur a la fourche ≤ 150 mm) dans un bassin versant du centre-ouest de l'Alberta. A la lumiere de leves par peche electrique a l'aide d'engins dorsaux dans 92 sites, nous avons evalue l'importance relative des caracteristiques d'habitats lotiques en ce qui concerne la probabilite de detection (p) et la possibilite que de fausses absences biaisent les estimations d'occupation. La distance mediane avant la premiere detection d'un omble a tete plate etait de 16 m (fourchette de 0 m a 289 m). Les modeles integrant la conductivite ambiante de l'eau comme covariable de la probabilite de detection performaient le mieux, une augmentation de 85 µS x [cm.sup.-1] se traduisant par la multiplication par plus de dix de la detection. La probabilite de detection conditionnelle a l'aide de l'engin de peche electrique dorsal approchait les 95 % dans les premiers 200 m d'effort dans les cours d'eau presentant une conductivite de l'ordre de 200 µS x [cm.sup.-1]. Le potentiel de fausses absences dans la region a l'etude etait relativement faible. L'occupation modelisee a l'echelle du site ([??] = 0,53; SE = 0,13) et de la parcelle ([??] = 0,47; SE = 0,12) correspondait etroitementaux estimations naives (0,47 et 0,43, respectivement, enpresumantque p = 1). Nos resultats soulignent les gains d'efficacite possibles decoulant d'une approche de modelisation de l'occupation pour l'evaluation de la repartition de poissons, un examen soigneux des hypotheses qui sous-tendent de tels modeles etant toutefois necessaire. [Traduit par la Redaction], Introduction Assessed as Threatened in the coterminous United States (USFWS 2008) and Alberta (Saskatchewan-Nelson rivers populations; COSEWIC 2012), bull trout (Salvelinus confluentus) are considered particularly sensitive to habitat change and [...]

The Sacramento splittail (Pogonichthys macrolepidotus) is a relatively large (400 mm), long-lived (8 years) demersal cyprinid of conservation importance endemic to the San Francisco Estuary (SFE), California, USA. It exhibits a semi-anadromous life cycle spending adult life in low to moderate salinity (0-12) habitat with migrations into upstream freshwater rivers and floodplains for spawning during winter-spring. The species persists as two genetically distinguishable populations--one dominant and one subordinate--separated by discrete spawning habitats that we suggest resemble an island-mainland metapopulation structure. The populations overlap in distribution in the SFE, yet segregation is maintained with individuals tending to aggregate or school with others of similar population heritage and natal origin. The populations are spatially connected via dispersal of the dominant population into the subordinate population's spawning habitat when climate patterns produce freshwater outflow sufficient to form a bridge of suitable low salinity habitat across the upper SFE. Habitat affinities of the two populations, hydrodynamic modeling studies, and historical outflow records together suggest such conditions occur in approximately 1/3 of years overall with an irregular frequency. This dynamic pattern of spatial connectivity controlled by climate variability may be an important driver of gene flow between the two populations. Pogonichthys macrolepidotus est un cyprinide demersal longevif (8 ans) relativement grand (400 mm) d'importance pour la conservation et endemique de l'estuaire de San Francisco (SFE; Californie, Etats-Unis). Il presente un cycle biologique semi-anadrome, passant sa vie adulte dans des habitats de salinite faible a moderee (0-12) avec des migrations dans des rivieres d'eau douce et des plaines alluviales situees plus en amont pour frayer a l'hiver et au printemps. L'espece persiste en deux populations genetiquement distinctes, une dominante et l'autre subordonnee, separees par des habitats de frai distincts qui ressemblent, selon nous, a une structure de metapopulation de type ile-continent. Si les aires de repartition des populations se chevauchent dans le SFE, une segregation est maintenue, les individus tendant a se regrouper ou former des bancs avec d'autres individus provenant de la meme population et de la meme origine natale. Les populations sont connectees dans l'espace par la dispersion de la population dominante dans l'habitat de frai de la population subordonnee quand les aleas du climat produisent des debits sortants d'eau douce assez importants pour former un pont d'habitats d'assez faible salinite de part en part du SFE superieur. La combinaison de l'affinite des habitats des deux populations, d'etudes de modelisation hydrodynamique et des registres historiques des debits sortants indiquerait que de telles conditions se produisent environ une annee sur trois, a une frequence irreguliere. Ce motif dynamique de connectivite spatiale controlee par la variabilite du climat pourrait etre une importante cause de flux genetique entre les deux populations. [Traduit par la Redaction], Introduction The extent to which discrete populations are connected by migration of individuals can substantially influence local and overall population dynamics, as well as the evolution and risk of extinction [...]

Intrinsic rebound potential, the demographic measure of a fish population's productivity that sustains a given mortality, relates to a species' resiliency and can be useful for understanding and evaluating the status of exploited populations, especially those poorly monitored and of low productivity, like many shark populations. The rebound potential is derived from the Euler-Lotka equation and, with the dynamics kept simple, is easily calculated for a given total mortality, needing only a species' age at maturity and its natural mortality (M). Its value can be quickly read from an isopleth diagram, whose contour pattern shows the interdependence of these two key parameters among different life histories. How the rebound potentials change as a function of age at maturity and the full range of possible M values also shows a way to estimate a species' natural mortality bounds. Importance of the age at maturity parameter is stressed. Le potentiel de rebond intrinseque, soit la mesure demographique de la productivite d'une population de poissons pouvant soutenir un taux de mortalite donne, est relie a la resilience de l'espece et peut etre utile pour comprendre et evaluer le statut de populations exploitees, en particulier les populations peu surveillees et de faible productivite, telles que celles de nombreux requins. Le potentiel de rebond est obtenu a partir de l'equation d'Euler-Lotka et, en maintenant une dynamique simple, se calcule facilement pour une mortalite totale donnee, ne necessitant que l'age de l'espece a la maturite et son taux de mortalite naturelle (M). Sa valeur peut etre tiree rapidement d'un diagramme d'isoplethes dont les courbes refletent l'interdependance de ces deux parametres cles pour differents cycles biologiques. Les variations du potentiel de rebond en fonction de l'age a la maturite et de la fourchette complete de valeurs de M possibles illustrent egalement un moyen d'estimer les limites de la mortalite naturelle d'une espece. L'age a la maturite est un parametre particulierement important. [Traduit par la Redaction], Introduction The Magnuson-Stevens Fishery Conservation and Management Reauthorization Act of 2006 required the US National Marine Fisheries Service (NMFS) to assume responsibility for establishing science-based annual catch limits and accountability [...]

Genetic analyses were undertaken on archived otoliths from juveniles representing historically strong year classes of northwest Atlantic redfish (Sebastes spp.) and on tissue samples from adults of known species and population of origin. The results indicated that the species composition of a year class is key information for understanding recruitment dynamics, with redfish species having distinct population-associated patterns of spatial dispersion. In the Gulf of St. Lawrence--Laurentian Channel area (GSL-LCH), the last strong year class (which supported the fishery for more than 30 years) belonged to Sebastes mentella and originated from the area. In contrast, four year classes that appeared abundant at young ages in research surveys in GSL-LCH but contributed only marginally to the adult population and the fishery of the region belonged to Sebastes fasciatus and carried the genetic signature of the adult population from the slope of the Newfoundland Grand Banks. Ocean currents and spatiotemporal trends in abundance-at-length suggest that the latter population uses the Gulf of St. Lawrence as a nursery area, with larvae and early juveniles drifting toward the Gulf of St. Lawrence and older juveniles migrating back to the slope of the Grand Banks after about 5-6 years. It is suggested that juvenile migration behaviour is a postsettlement process that plays an important role in redfish recruitment dynamics and carries both demographic and evolutionary implications. Des analyses genetiques ont ete realisees a partir d'otolithes archives appartenant aux juveniles de fortes classes d'age historiques de sebaste (Sebastes spp.) du nord-ouest Atlantique et d'echantillons de tissu preleves sur des adultes d'espece et de population d'origine connues. Les resultats ont montre que la composition specifique d'une classe d'age constitue une information clef pour la comprehension de la dynamique de recrutement, en revelant que les especes de sebaste ont des patrons de dispersion spatiale distincts et propres aux populations. Dans la region du Golfe du Saint-Laurent et du chenal Laurentien (GSL-LCH), la derniere forte classe d'age (qui a supporte la peche pendant plus de 30 ans) appartenait a Sebastes mentella et etait originaire de la region. Par contre, quatre classes d'age qui semblaient abondantes a un jeune age dans les releves de recherche du GSL-LCH, mais qui ont contribue seulement marginalement a la population adulte et a la peche de la region, appartenaient a Sebastes fasciatus et portaient la signature genetique de la population adulte distribuee le long de la pente des Grands Bancs de Terre-Neuve. Les courants oceaniques et les tendances spatiotemporelles d'abondance en fonction de l'age suggerent que cette derniere population utilise le Golfe du Saint-Laurent comme zone de nurserie; les larves et jeunes juveniles deriveraient vers le Golfe du Saint-Laurent puis, 5 a 6 ans plus tard, les juveniles plus ages retourneraient vers la pente des Grands Bancs. Il est suggere que le comportement migratoire des juveniles joue un role significatif dans la dynamique de recrutement du sebaste et possede des implications aux niveaux demographique et evolutif., Introduction Episodic recruitment is commonly observed in long-lived marine teleost species, such as Sebastes spp. (Longhurst 2002; Love et al. 2002; Planque et al. 2012; Ralston et al. 2013). The [...]

We evaluated the scope for improving abundance forecasts for fishery management using Sacramento River fall Chinook salmon (Oncorhynchus tshawytscha) as a case study. A range of forecast models that related the Sacramento Index (SI; an index of adult ocean abundance) to jack (estimated age 2) spawning escapement the previous year were considered. Alternative models incorporated effects of density dependence, local environmental conditions, the abundance of the previous cohort, and trends or autocorrelation in the jack-to-SI relationship. Forecast performance was assessed in terms of bias, accuracy, ability to track trends in the SI, and management objectives. Several models achieved higher accuracy than the model used for management, but no single model performed best across all criteria, and substantial forecast error remained across all approaches considered. Environmental models generally performed better than the management model, but there were differences in the relative importance of individual environmental variables over time and among model formulations. Accounting for model selection uncertainty in environmental models decreased their forecast performance. Simpler models often had similar or better performance than environmental models. In particular, the model incorporating temporally autocorrelated errors demonstrated potential for modest forecast improvement with relatively little additional model complexity. Nous avons evalue le potentiel d'amelioration des previsions d'abondance pour la gestion des peches en utilisant le saumon quinnat (Oncorhynchus tshawytscha) d'automne du fleuve Sacramento comme etude de cas. Divers modeles de prevision reliant l'indice Sacramento (SI; un indice de l'abondance oceanique des adultes) a l'echappee de geniteurs unibermarins (age estime de 2 ans) l'annee precedente ont ete examines. Les modeles incorporaient, selon le cas, les effets de la dependance sur la densite, des conditions ambiantes locales, de l'abondance de la cohorte precedente et des tendances ou de l'autocorrelation du lien unibermarins-SI. La performance de prevision a ete evaluee en termes des biais, de l'exactitude, de la capacite de faire ressortir des tendances du SI et des objectifs de gestion. Plusieurs modeles ont produit une plus grande exactitude que le modele utilise pour la gestion, mais aucun modele n'a surclasse les autres pour tous les criteres, et des erreurs de prevision importantes subsistaient pour toutes les approches examinees. Les modeles environnementaux donnaient generalement de meilleurs resultats que le modele de gestion, mais il y avait des differences en ce qui concerne l'importance relative de variables environnementales precises dans le temps et entre les formulations de modele. La prise en compte de l'incertitude associee au choix du modele dans les modeles environnementaux reduisait leur performance de prevision. Dans bien des cas, les modeles plus simples performaient aussi bien ou mieux que les modeles environnementaux. Plus particulierement, le modele incorporant les erreurs autocorrelees dans le temps a demontre un potentiel d'amelioration modeste des previsions pour une augmentation relativement limitee de la complexite du modele. [Traduit par la Redaction], Introduction Forecasting of population abundance and recruitment is a key element of the management of many fisheries. These forecasts are used to define catch limits and allowable exploitation rates through [...]

In any stock assessment application, the implicit assumptions regarding spatial population structure must be carefully evaluated. Tag-integrated models offer a promising approach for incorporating spatial structure and movement patterns in stock assessments, but the complexity of the framework makes implementation challenging and the appraisal of performance difficult. A flounder-like fishery was simulated to emulate the metapopulation dynamics of the three yellowtail flounder (Limanda ferruginea) stocks off New England, and the robustness of spatially explicit tag-integrated models were compared with closed population assessments. Different movement parametrizations and data uncertainty scenarios were simulated, while the ability of the tag-integrated model to estimate reporting rate and time-varying movement were also evaluated. Results indicated that the tag-integrated framework was robust for the simulated fishery across a wide range of connectivity levels and that tag reporting rates were accurately estimated. Closed population models also demonstrated limited error. Therefore, spatially explicit approaches may not always be warranted even when regional connectivity is occurring, but tag-integrated models can provide improved parameter estimates when reliable tagging data are available. Tag-integrated models also serve as valuable tools for informing spatially explicit operating models, which can then be used to evaluate the assumptions and performance of closed population models. Dans toute application devaluation des stocks, les hypotheses implicites concernant la structure spatiale de la population doivent faire l'objet d'une evaluation soigneuse. Si les modeles integrant les donnees de marquage constituent une approche prometteuse pour incorporer la structure spatiale et les motifs de deplacement aux evaluations des stocks, la complexite de leur cadre en rend l'application compliquee et revaluation de la performance difficile. Une peche s'apparentant a la peche a la limande a ete simulee pour reproduire la dynamique de metapopulation des trois stocks de limandes a queue jaune (Limanda ferruginea) au large de la Nouvelle-Angleterre, et la robustesse de modeles spatialement explicites integrant le marquage a ete comparee avec des evaluations de population fermee. Differentes parametrisations des deplacements et differents scenarios d'incertitude des donnees ont ete simules, et la capacite du modele integrant le marquage a estimer les taux de declaration et les deplacements variables dans le temps ont aussi ete evalues. Les resultats indiquent que le cadre integrant les donnees de marquage est robuste pour la peche simulee pour une grande fourchette de niveaux de connectivite et que les taux de declaration des marques etaient estimes avec exactitude. Les modeles de population fermee presentaient egalement des erreurs restreintes. Ainsi, si les approches spatialement explicites ne sont pas toujours necessaires meme quand il y a connectivite regionale, les modeles integrant le marquage peuvent toutefois fournir de meilleures estimations des parametres quand des donnees de marquage fiables sont disponibles. Les modeles integrant les donnees de marquage constituent egalement de bons outils pour alimenter les modeles d'exploitation spatialement explicites, qui peuvent ensuite etre utilises pour evaluer les hypotheses et la performance des modeles de population fermee. [Traduit par la Redaction], Introduction Spatial population structure and movement patterns play a critical role in the regulation of abundance (Cadrin and Secor 2009). Attempting to incorporate the intricacies of fine-scale population structure into [...]

Arctic marine food webs are centered on polar cod (Boreogadus saida), a small, largely pelagic gadid, which movement and migration remain unclear, especially for the early life stages. The present study examined the otolith chemistry of juvenile polar cod from six oceanographic regions of the Arctic Ocean in order to document patterns of spatial segregation, dispersion and migration during the species early life. The freshwater winter refuge hypothesis, suggesting that polar cod larvae start to hatch in winter in freshwater-influenced regions but only later in the season in purely marine regions, was also tested. Five elemental ratios (Li/Ca, Mg/Ca, Mn/Ca, Sr/Ca and Ba/Ca) were analyzed by laser ablation inductively coupled plasma mass spectrometry in three otolith zones representing the egg, larval and juvenile stages. The concentration of each of the five elements at the edge of the otoliths, corresponding to incorporation shortly before capture, was significantly correlated with surface salinity and temperature at capture site and date. Otolith chemistry differed between juveniles from freshwater-influenced regions (Laptev Sea, Hudson Bay Amundsen Gulf) and those from purely marine regions (Lancaster Sound, Baffin Bay, Frobisher Bay), in agreement with dissolved concentrations of at least some of the target elements in the Arctic Ocean. Discriminant function analyses including all five elements provided valuable information on the species population structure and dispersion of early stages. The correspondence between otolith Mn/Ca, Ba/Ca and vertical profiles of dissolved Mn and Ba in the water column may reflect the ontogenetic vertical migration of juvenile polar cod in late-summer and fall., Author(s): Caroline Bouchard[sup.1] , Simon R. Thorrold[sup.2] , Louis Fortier[sup.1] Author Affiliations: (1) Quebec-Ocean, Departement de Biologie, Universite Laval, G1V 0A6, Quebec, QC, Canada (2) Biology Department MS 50, Woods [...]

Redd surveys are used extensively to estimate spawner population size for Pacific salmon (Onchorynchus spp.). Because redds tend to be spatially aggregated, estimates of total redds based on subsamples of the potential spawning grounds can be uncertain unless the spatial structure is accounted for. Here we use known redd locations for three populations over several years to compare five different probability sampling designs through simulation. The coefficient of variation (CV) for estimates based on simple random sampling was high, with values well over 15% when sampling a third of the reaches. Moving to a spatially balanced sampling design (generalized random tessellation stratified; GRTS) produced improvements in two of the three watersheds (16%-22% reduction in CV). Estimates based on a stratified GRTS design and a GRTS design that included a census of all reaches close to the peak count had higher accuracy, with an approximate CV of one-half to one-third of GRTS alone. We show how these improvements are predicted by theory and under which conditions the different approaches are likely to perform well. Les denombrements de nids de frai sont largement utilises pour estimer la taille de populations de geniteurs de saumons du Pacifique (Onchorynchus spp.). Etant donne que les nids de frai sont souvent regroupes dans l'espace, les estimations de leur nombre total reposant sur des sous-echantillons des lieux de frai potentiels peuvent s'averer incertaines si la structure spatiale n'est pas prise en consideration. Nous utilisons des emplacements connus de nids de frai pour trois populations sur plusieurs annees afin de comparer par simulation cinq plans d'echantillonnage aleatoire differents. Les coefficients de variation (CV) pour les estimations basees sur un echantillonnage aleatoire simple etaient eleves, les valeurs depassant de beaucoup 15 % quand un tiers des tronqons etait echantillonne. L'utilisation d'un plan d'echantillonnage spatialement equilibre (stratifie par tessellation aleatoire generalisee; GRTS) a produit des ameliorations pour deux des trois bassins versants (reduction de 16 % a 22 % des CV). Les estimations basees sur un plan GRTS stratifie et un plan GRTS qui inclue le recensement de tous les tronqons situes a proximite du maximum de nids denombres presentaient une plus grande exactitude, les CV approximatifs allant de la moitie au tiers du CV pour le GRTS seul. Nous demontrons que ces ameliorations sont predites par la theorie et illustrons dans quelles conditions ces differentes approches sont susceptibles de donner de bons resultats. [Traduit par la Redaction], Introduction Estimates of adult spawning escapement are essential for monitoring salmon population status and trends, developing biological reference points for fisheries, and evaluating the effectiveness of hatcheries and restoration actions [...]

ABSTRACT. Atlantic mackerel (Scomber scombrus) were recorded in Isfjorden, Svalbard (78'15' N, 15°1T E) in late September 2013. This record is the northernmost known occurrence of mackerel in the Arctic [...]

Recent studies have indicated that in fish populations performing diel vertical migrations (DVM), some individuals do not migrate but reflect a resident phenotype, a pattern named as partial DVM. I present data on fish densities and the proportion of residents in Lake Stechlin (Germany) as obtained by annual midwater trawling over four discrete depths during nighttime over 8 years. The lake is inhabited by the sympatric vendace (Coregonus albula) and Fontane cisco (Coregonus fontanae). The proportion of vendace residents increased with the density of vendace, whereas the proportion of Fontane cisco residents declined with increasing density, indicating that density plays a role in the migration patterns for both species, but in opposite directions. There were almost no differences in mean size, size-frequency distributions, or Fulton condition factor between resident or migrant parts of the populations in both species. However, the proportion of dry mass in wet mass, which indicates individual nutritional status, had a tendency to be lower in migrants than in residents in both species in the years 2011,2012, and 2013. These data suggest that density dependence may be an important factor that modifies the proportion of residents in vertically migrating fish populations. In contrast, length-dependent predation vulnerability or systematic individual differences in nutritional status were not strongly supported as potential predictors of the proportion of residents. It needs to be discussed whether partial DVM is conceptually similar to partial seasonal migrations of fish, or whether DVM reflects variants of the ideal free distribution, which are inherently density-dependent. Des etudes recentes indiquent que, dans les populations de poissons caracterisees par des migrations verticales nycthemerales (MVN), certains individus ne migrent pas, refletant un phenotype resident, un motif appele MVN partielle. Je presente des donnees sur la densite de poissons et la proportion de residents dans le lac Stechlin (Allemagne), obtenues par peche annuelle au chalut pelagique a quatre profondeurs differentes durant la nuit, sur une periode de 8 ans. Le lac abrite le coregone blanc (Coregonus albula) et le coregone de Fontane (Coregonus fontanae), des especes sympatriques. La proportion de coregones blancs residents a augmente parallelement a la densite de cette espece, alors que la proportion de coregones de Fontane residents a diminue parallelement a une augmentation de leur densite, ce qui indique que la densite joue un role, bien que de sens opposes, dans les habitudes migratoires des deux especes. Il n'y avait presque aucune difference sur le plan de la taille moyenne, des distributions de frequences de taille ou du facteur de condition de Fulton entre les parties residentes et migratrices des populations des deux especes. Cependant, la proportion de masse seche dans la masse humide, qui indique l'etat nutritionnel individuel, tendait a etre plus faible chez les migrants que chez les residents des deux especes pour les annees 2011, 2012 et 2013. Ces donnees donnent a penser que la dependance a la densite pourrait etre un important facteur de modification de la proportion de residents dans les populations de poissons a migration verticale nycthemerale. En revanche, les donnees n'appuient pas fortement la notion voulant que la vulnerabilite a la predation dependante de la longueur ou des differences individuelles systematiques de l'etat nutritionnel constituent de possibles variables explicatives de la proportion de residents. Il convient d'examiner si la MVN partielle est conceptuellement semblable aux migrations saisonnieres partielles de poissons ou si la MVN reflete des variantes de la distribution libre ideale qui sont intrinsequement dependantes de la densite. [Traduit par la Redaction], Introduction Diel vertical migration (DVM) is a common behaviour of fish in freshwater and marine habitats. Typically, pelagic fish ascend during dusk from their deeper daytime habitats into shallower layers [...]

ABSTRACT. Eight cold-water streams in Lake and Geauga Counties, Ohio were evaluated to revise a predictive model for assessing streams for future introduction of threatened native Ohio brook trout (Salvelinus [...]

With the decline of many exploited fish populations, catch and release has become an increasingly used management practice to allow sport fishing while reducing its impact on wild populations. However, survival and reproductive success can vary according to the catch and release technique and environmental conditions, suggesting a potential impact of this practice on prespawning behaviour. Here we evaluate how some critical aspects of salmon freshwater migration are influenced by catch and release and by environmental factors. For this purpose, 40 multi-sea-winter Atlantic salmon (Salmo salar) (20 catch and release and 20 control) were followed by telemetry from June 2011 to March 2012. Temperature was found to influence movements and the daily probability that a fish would cross a fish ladder, while water discharge influenced daily distance travelled during the prespawning migration. Catch and release was found to influence the daily probability of fish to cross a barrier as well as the total distance traveled in the river. Overall, this study suggests that salmon caught and released by fishermen survive and reproduce, but that prespawning exploration behaviours could be altered compared with those of uncaught salmon. Avec le declin de plusieurs populations de poissons exploitees, la remise a l'eau est devenue une approche de gestion populaire afin d'assurer la peche sportive tout en minimisant ses impacts. Neanmoins, comme la survie et le succes reproducteur peuvent varier selon les conditions environnementales et la methode employee, la remise a l'eau pourrait avoir un impact non-negligeable sur le comportement pre-reproducteur. Cette etude evalue comment certains aspects critiques de la migration en eau douce du saumon atlantique (Salmo salar) sont influences par la remise a l'eau et les conditions environnementales. Quarante saumons redibermarins (20 remis a l'eau, 20 controles) ont ete suivis par telemetrie de juin 2011 a mars 2012. Les resultats indiquent que la temperature influence la probabilite de mouvement et de franchissement d'obstacle, alors que le debit influence la distance journaliere parcourue. Par ailleurs, la remise a l'eau influence la probabilite journaliere pour un individu de franchir un obstacle et la distance totale parcourue par celui-ci. Cette etude suggere que meme si les saumons remis a l'eau survivent et se reproduisent, le comportement pre-reproducteur peut en etre altere., Introduction As is the case with many other fishes worldwide, Atlantic salmon (Salmo salar) has been declining rapidly since the middle of the 20th century and is now near historic [...]

Improved methods are needed to evaluate barriers and traps for control and assessment of invasive sea lamprey (Petromyzon marinus) in the Great Lakes. A Bayesian state-space model provided reach-specific probabilities of movement, including trap capture and dam passage, for 148 acoustic tagged invasive sea lamprey in the lower Cheboygan River, Michigan, a tributary to Lake Huron. Reach-specific movement probabilities were combined to obtain estimates of spatial distribution and abundance needed to evaluate a barrier and trap complex for sea lamprey control and assessment. Of an estimated 21828 29 300 adult sea lampreys in the river, 0%-2%, or 0-514 untagged lampreys, could have passed upstream of the dam, and 46%- 61% were caught in the trap. Although no tagged lampreys passed above the dam (0/148), our sample size was not sufficient to consider the lock and dam a complete barrier to sea lamprey. Results also showed that existing traps are in good locations because 83%-96% of the population was vulnerable to existing traps. However, only 52%-69% of lampreys vulnerable to traps were caught, suggesting that traps can be improved. The approach used in this study was a novel use of Bayesian state- space models that may have broader applications, including evaluation of barriers for other invasive species (e.g., Asian carp (Hypophthalmichthys spp.)) and fish passage structures for other diadromous fishes. Il est necessaire d'ameliorer les methodes d'evaluation des barrieres et pieges utilises pour controler et evaluer la lamproie marine (Petromyzon marinus), une espece envahissante, dans les Grands Lacs. Un modele bayesien d'espace d'etats a produit des probabilites de deplacement, dont le piegeage et le passage de barrage, dans differents biefs pour 148 lamproies marines envahissantes dotees de marques acoustiques dans le cours inferieur de la riviere Cheboygan (Michigan), un affluent du lac Huron. Les probabilites de deplacement propres au bief ont ete combinees pour obtenir les estimations de la repartition spatiale et de l'abondance requises pour evaluer un complexe de barriere et piege pour le controle et l'evaluation des lamproies. Sur un nombre estime de 21828 a 29 300 lamproies adultes dans la riviere, de 0 % a 2 % des lamproies non marquees, soit de 0 a 514 poissons, pourraient etre passees en amont du barrage, et de 46 % a 61 % ont ete prises dans le piege. Bien qu'aucune lamproie marquee ne soit passee en amont du barrage (0/148), la taille de l'echantillon est trop petite pour permettre d'etablir que l'ecluse-barrage constitue une barriere completement etanche au passage des lamproies. Les resultats ont egalement demontre que les pieges existants sont bien situes, puisque de 83 % a 96 % de la population etait vulnerable aux pieges existants. Cependant, de 52 % a 69 % seulement des lamproies vulnerables aux pieges ont ete capturees, indiquant que ces pieges peuvent etre ameliores. L'approche employee constitue une utilisation novatrice des modeles bayesiens d'espace d'etats qui pourrait avoir des applications plus larges, notamment pour l'evaluation des barrieres au passage d'autres especes envahissantes (p. ex. carpe asiatique (Hypophthalmichthys spp.)) et des passes a poissons pour d'autres especes diadromes. [Traduit par la Redaction], Introduction The Laurentian Great Lakes were severely disrupted by the arrival of invasive sea lamprey (Petromyzon marinus) through the Welland Canal in the early 1900s (Smith and Tibbles 1980; Hansen [...]

Density-dependent processes resulting from fish stocking were demonstrated to have a significant impact on recreational fishery performance, and this case study will be of use to guide fish stocking decisions in other fisheries. We evaluated a put-grow-and-take lake fishery stocking program for Chinook salmon (Oncorhynchus tshawytscha) located in south-western Victoria, Australia. We hypothesised that recreational fishery performance would show significant density-dependent relationships with fish stocking. To test this hypothesis, we used Wald F tests in a general linear regression model to evaluate relationships between a long-term historical fish stocking program and fishery performance, including angler and net catch rates and weight, length, and condition of caught fish. Our results yielded (i) significant positive relationships between angler and net catch rate of Chinook salmon with the number of Chinook salmon stocked in the same year and (ii) significant negative relationships between the weight of angler-caught Chinook salmon with both the number of Chinook salmon stocked in the same year and total number of fish stocked (apart from Chinook salmon) over the previous three year period. Il a deja ete demontre que les processus dependants de la densite qui resultent de l'empoissonnement ont une importante incidence sur le rendement des peches recreatives, et la presente etude de cas servira a orienter les decisions relatives a l'empoissonnement dans d'autres peches. Nous avons evalue un programme d'empoissonnement pour une peche de lac au saumon quinnat (Oncorhynchus tshawytscha) de type depot-retrait dans le sud-ouest de l'Etat de Victoria (Australie). Nous avons postule qu'il devrait y avoir des relations dependantes de la densite significatives entre le rendement de la peche recreative et l'empoissonnement. Pour verifier cette hypothese, nous avons utilise des tests F de Wald dans un modele de regression lineaire generale pour evaluer les liens entre un programme d'empoissonnement historique de longue duree et le rendement des peches, dont les taux de prises a la ligne et au filet, et le poids, la longueur et l'embonpoint des poissons peches. Nos resultats revelent (i) des relations positives significatives entre le taux de prises a la ligne et au filet de saumons quinnats et le nombre de saumons quinnats empoissonnes la meme annee et (ii) des relations negatives significatives entre le poids des saumons quinnats peches a la ligne et tant le nombre de saumons quinnats empoissonnes la meme annee que le nombre total de poissons empoissonnes (autres que des saumons quinnats) au cours des trois annees precedentes. [Traduit par la Redaction], Introduction Fish populations are subject to limited resources causing density dependence or density independence in vital rates of growth, mortality, and reproduction of individuals (hereafter density-dependent processes). Density-dependent processes in [...]

To address the lack of fisheries-independent information for Atlantic bigeye tuna (Thunnus obesus), we released 21 adults (131 ± 12 cm curved fork length) between 2008 and 2010 in the Sargasso Sea and Northwest Atlantic. Data from nine tags (range: 1-292 days; mean: 89 days) revealed (i) pronounced north-south movements in pelagic waters between areas including Georges Bank, Mid- and South Atlantic Bight, Caribbean Sea, and Brazilian shelf, (ii) a lack of east-west exchange, and (iii) a high-use area in the Hatteras Plain, centered southwest of Bermuda. Bigeye tuna occupied water masses of 2.7-28.2°C and depths of 0-1280 m, with deeper depths in the daytime (daily mean ± standard deviation: 196 ± 92 m) than at nighttime (45 ± 29 m). Even though bigeye tuna are assumed to forage on the deep scattered layer during the day, generalized additive mixed models did not identify the deep scattered layer as an important predictor of daytime swimming depth. Model results highlight the importance of geographic location in influencing habitat utilization, and thus suggest the need for fisheries- independent monitoring in high-catch areas, such as the central and equatorial Atlantic. Pour pallier l'absence d'information independante des peches concernant le thon obese (Thunnus obesus)de l'Atlantique, nous avons relache 21 adultes (131 ± 12 cm longueur a la fourche incurvee) de 2008 a 2010, dans la mer des Sargasses et le nord-ouest de l'Atlantique. Des donnees de neuf etiquettes (intervalle : 1-292 jours; moyenne: 89 jours) ont revele (i) des deplacements nord-sud marques dans les eaux pelagiques entre differentes regions dont le banc de Georges, les golfes medio- et sud-atlantiques, la mer des Caraibes et le plateau bresilien, (ii) l'absence d'echanges est-ouest et (iii) une region de forte utilisation dans la plaine abyssale d'Hatteras, centree au sud-ouest des Bermudes. Les thons obeses occupaient des masses d'eau de 2,7°C a 28,2°C et des profondeurs de 0 ma 1 280 m, preferant de plus grandes profondeurs le jour (moyenne quotidienne ± SD: 196 ± 92 m) que la nuit (45 ± 29 m). Meme s'il est presume que les thons obeses se nourrissent dans la couche diffusante profonde le jour, des modeles mixtes additifs generalises n'ont pas etabli que la couche diffusante profonde etait une importante variable predictive de la profondeur de nage diurne. Les resultats des modeles mettent en evidence l'importante influence de l'emplacement geographique sur l'utilisation de l'habitat, soulignant ainsi la necessite d'une surveillance independante des peches dans les regions de forte capture comme l'Atlantique central et equatorial. [Traduit par la Redaction], Introduction Bigeye tuna (Thunnus obesus) is one of the most important commercial tuna species in the Atlantic. It is most commonly found in tropical and subtropical waters, but is fished [...]

Downstream migration of silver American eels (Anguilla rostrata) from the St. Lawrence system was examined using acoustic telemetry. One hundred and thirty six silver American eels were tagged, and their passage was recorded using fixed acoustic arrays covering a 420 km distance along the St. Lawrence River and Estuary. Eighty-nine percent of the tagged eels were detected. All migrant eels (111) exhibited unidirectional and downstream movements, but the migration was not completed in one continuous direct movement. High individual variability in migratory longitudinal profiles was documented as well as in individual speed with no apparent relation to river discharge or morphological traits. Migration speed increased over the season. Our observations demonstrated that migrating silver American eels are largely nocturnal and demonstrated the use of nocturnal, ebb tide transport to leave the estuary. With 44 additional eels tagged and released in the maritime estuary, escapement of 180 silver American eels from the Gulf of St. Lawrence system was monitored along a 125 km acoustic line that entirely covered Cabot Strait in 2011. Surprisingly, only four of the tagged eels were recorded escaping the Gulf of St. Lawrence. La migration de devalaison de l'anguille d'Amerique argentee (Anguilla rostrata) a ete etudiee grace a un systeme de telemetrie acoustique. Cent trente-six anguilles argentees ont ete marquees et leur passage ou presence a ete enregistre grace a des lignes acoustiques fixes couvrant une distance de 420 km le long du fleuve et de l'estuaire du St-Laurent. Quatre-vingt neuf pourcent des anguilles marquees ont ete detectees. Toutes les anguilles migrantes (111) montrent des mouvements unidirectionnels vers l'aval mais la migration n'est pas menee d'une seule traite. Une tres grande variabilite individuelle au niveau des profils de migration a ete demontree, ainsi qu'au niveau des vitesses de migration sans que ces dernieres ne puissent etre reliees ni au debit du fleuve ni a des traits morphologiques. La vitesse de migration augmente au cours de la saison. Nos observations suggerent l'utilisation du transport de jusant nocturne pour quitter l'estuaire. Avec 44 anguilles supplementaires marquees et relachees en estuaire maritime, l'echappement de 180 anguilles argentees du systeme St-Laurent a ete suivi grace a une ligne acoustique couvrant les 125 km du detroit de Cabot en 2011. Etonnamment, seulement quatre des anguilles marquees sortant du Golfe du St-Laurent ont ete detectees., Introduction The American eel (Anguilla rostrata) and the European eel (Anguilla anguilla) are facultative catadromous fishes inhabiting continental waters in fresh, brackish, or saltwater environments (e.g., Daverat et al. 2006), [...]

Density-dependent mortality in young life stages should strongly limit the potential for additive effects caused by stocking of fish sizes that are smaller than size at recruitment into the fishery. Indeed, stocking models have suggested that stocking of fry should not elevate year class strength in self-sustaining stocks. However, limited data based on replicated and controlled experiments are available to support this prediction. We performed a pond experiment (N = 4 per treatment) to compare the stock enhancing outcome of stocking hatchery-reared northern pike (Esox lucius) fry and the natural production of young in self-recruiting pike populations. We also added a treatment where pike fry were stocked into ponds that otherwise did not have pike to mimic the absence of natural recruitment. Fry stocking into self-reproducing stocks did not elevate year class strength over unstocked controls. However, in the absence of competition, year class strength of juveniles in late summer emerging from fry stocking was similar to the production of natural recruits. Overall, we demonstrated the competitive disadvantage of hatchery-reared fry when released into waters already containing natural recruits, the partial replacement of natural recruits by hatchery-reared fry, and the lack of additive effects of stock enhancement in naturally reproducing stocks. A stock-enhancing effect of pike fry stocking may only be expected in the absence of natural recruitment. La mortalite dependante de la densite durant les premieres etapes du cycle de vie devrait fortement limiter la possibility d'effets additifs causes par l'empoissonnement avec des poissons de tailles plus petites que la taille au moment du recrutement dans la peche. De fait, des modeles d'empoissonnement donnent a penser que l'empoissonnement avec des alevins ne devrait pas accroitre la force des classes d'age dans les stocks dont le maintien est assure par la reproduction naturelle. Cependant, il y a peu de donnees issues d'experiences repetees et controlees disponibles pour appuyer cette prediction. Nous avons realise une experience en etang (N =4 par traitement) pour comparer les resultats de la valorisation du stock par empoissonnement avec des alevins d'elevage de grand brochet (Esox lucius)a la production naturelle de juveniles dans des populations de brochets maintenues par autorecrutement. Nous avons egalement inclus un traitement dans lequel des alevins de brochet etaient empoissonnes dans des etangs par ailleurs exempts de brochets afin de reproduire l'absence de recrutement naturel. L'empoissonnement d'alevins dans des stocks autoreproducteurs n'a pas rehausse la force des classes d'age par rapport a celle de populations temoins non empoissonnees. Cependant, en l'absence de concurrence, la force des classes d'age a la fin de l'ete de juveniles issus de l'empoissonnement avec des alevins etait semblable a celle decoulant de la production de recrues naturelles. En general, nous demontrons le desavantage concurrentiel des alevins d'elevage relaches dans des eaux qui renferment deja des recrues naturelles, le remplacement partiel de recrues naturelles par des alevins d'elevage et l'absence d'effets additifs de la valorisation du stock dans des stocks se reproduisant de maniere naturelle. Un effet de valorisation du stock par l'empoissonnement avec des alevins de brochet ne serait a prevoir qu'en l'absence de recrutement naturel. [Traduit par la Redaction], Introduction Stocking is conducted for multiple reasons, ranging from conservation of threatened fish species to enhancement of fisheries quality (Lorenzen et al. 2012). One common fisheries objective is the enhancement [...]

Understanding mortality rates and movement patterns across a species' distribution can provide key insight necessary for developing effective conservation, recovery, and management plans. We directly estimated site fidelity and natural mortality rates for the threatened Gulf sturgeon (Acipenser oxyrinchus desotoi) across a large portion of their range in the northern Gulf of Mexico using acoustic telemetry methods and a simulation-tested, multistate mark-recapture model. Our results suggest that fidelity rates to riverine habitats used during spring and summer are high, but natural mortality rates vary widely. Our results are highly relevant for managing this species. The high fidelity rates, coupled with supporting genetic analyses, suggest that management of individual riverine populations of Gulf sturgeon should be considered. The need for individual river-based management is exacerbated by the variation in natural mortality rates among rivers. The reasons for these differences in mortality are unclear, but are an important area of future research because higher mortality rates may impede recovery of some Gulf sturgeon populations to stated management targets. La comprehension des taux de mortalite et des habitudes de deplacement dans l'aire de repartition d'une espece peut fournir des renseignements cles necessaires a l'etablissement de plans de conservation, de retablissement et de gestion efficaces. Nous avons estime directement les taux de fidelite au site et de mortalite naturelle pour l'esturgeon du golfe du Mexique (Acipenser oxyrinchus desotoi), une espece menacee, dans une grande partie de son aire de repartition dans le nord du golfe du Mexique, en utilisant des methodes de telemetrie acoustique et un modele de marquage-recapture multi-etats valide par simulation. Nos resultats donnent a penser que les taux de fidelite aux habitats fluviaux utilises durant le printemps et l'ete sont eleves, mais que les taux de mortalite naturelle varient considerablement. Ces resultats revetent une grande pertinence pour la gestion de cette espece. Les taux de fidelite eleves, combines a des analyses genetiques les appuyant, indiqueraient que la possibilite de gerer individuellement les differentes populations fluviales d'esturgeons du golfe du Mexique devrait etre examinee. La variabilite des taux de mortalite naturelle d'une riviere a l'autre rend d'autant plus necessaire une telle gestion individuelle axee sur la riviere. Si ses causes ne sont pas bien comprises, cette variabilite de la mortalite constitue neanmoins une importante avenue de recherche future puisque des taux de mortalite eleves peuvent entraver le retablissement de certaines populations d'esturgeons du golfe du Mexique aux cibles de gestion etablies. [Traduit par la Redaction], Introduction Understanding how fish populations are spatially distributed is a common need in developing effective conservation and management plans. It is important to establish the sources, levels, and patterns of [...]

Movement of fishes defines the distribution and abundance of populations and occurs on a range of spatial and temporal scales. To successfully parameterise assessments and design management strategies for exploited fish populations, knowledge and consideration of their movement patterns are essential. Since the efficacy of management approaches vary depending on the sedentary or mobile nature of the target species, presence, space use and depth utilization were examined to understand the movement patterns of redthroat emperor Lethrinus miniatus. Sixty individuals were monitored for up to 12 months in an acoustic array comprising three coral reefs, and variation in space use and movement patterns was observed among 26 individuals. Half of the individuals were recorded only in proximity of one receiver along the reef edge, while the other half were detected at multiple receivers and used horizontal areas of approximately 4 [km.sup.2]. Periods of non-detection and lower detection frequency at night ([[chi square].sub.1] = 342.157, P < 0.001) indicated individuals may move away from the monitored reef edge to the adjacent sandy habitat, but most movements outside the array remain unknown. Long-distance movement was recorded for one individual, recaptured ~160 km from the release location. Generally, no trends in depth use were apparent, L. miniatus inhabited a variety of depths, which were not related to individual size or time of day, yet some effect of month was evident. Variation in movement among adult L. miniatus indicates that while some individuals undergo broaderscale movement, spatial closures that cover individual reefs (>4 [km.sup.2]) could provide protection from fishing for the proportion of the population that displayed high site fidelity and moderate-sized activity spaces (over a period of up to 12 months)., Introduction Movement defines the distribution of species in time and space, and knowledge of movement patterns is useful for understanding population dynamics and potential effects of exploitation (Pittman and McAlpine [...]

Tag shedding rates are estimated for southern bluefin tuna (SBT, Thunnus maccoyii) from double-tagging data arising from two tagging studies run in the 1990s and 2000s. Since the early 1990s, a high proportion of SBT tag recoveries has been sourced from juveniles captured by purse seine vessels in the Great Australian Bight and transferred to tuna farms off Port Lincoln in the state of South Australia. When tags have been shed by wild-caught SBT fattened in tuna farms, it is generally not known if the tags were shed in the open ocean before purse seine capture or after purse seine capture while the fish were on farm. Using a Bayesian approach, we fit separate tag retention curves for time in the ocean and time on farms as Weibull distribution reliability functions. The study suggests SBT shed tags at a much higher rate in on-farm enclosures than in the open ocean. Biofouling on tags in tuna farms may contribute to higher tag shedding rates. Les taux de perte d'etiquettes sont estimes pour le thon rouge du Sud (TRS, Thunnus maccoyii) a partir de donnees de marquage double tirees de deux etudes de marquage menees dans les annees 1990 et 2000. Depuis le debut des annees 1990, une forte proportion d'etiquettes de TRS recuperees proviennent de juveniles captures par des navires a senne coulissante dans la Grande Baie australienne, puis transferes dans des elevages de thons au large de Port Lincoln, dans l'Etat d'Australie-Meridionale. Quand les etiquettes perdues proviennent de TRS captures dans la nature et engraisses dans des elevages, on ne sait generalement pas si elles ont ete perdues en pleine mer avant la capture par senne coulissante ou apres cette capture, alors que les poissons etaient en elevage. En utilisant une approche bayesienne, nous avons cale differentes courbes de retention d'etiquettes pour le temps passe en pleine mer et le temps passe en elevage en tant que fonctions de fiabilite de la distribution de Weibull. L'etude donne a penser que les TRS se departet de leurs etiquettes aun tauxbeaucoup plus eleve dans lesbassins d'elevage qu'en pleine mer. L'encrassementbiologique des etiquettes dans les elevages pourrait en partie expliquer les taux plus eleves de perte d'etiquettes. [Traduit par la Redaction], Introduction Tag recovery data from fish tagging studies are used to estimate a range of quantities important for the management of harvested fish stocks. Some information, such as growth rates [...]

Abstract.--The California spiny lobster (Panulirus interruptus) fishery in southern California ranks amongst the State's most economically important fisheries. An analysis of commercial harvest data confirms that the fishery was landing [...]

We previously developed an individual-based model evaluating the bio-economic efficiency of fishing vessel movements from recent high resolution spatial fishery data. The assumption was constant underlying resource availability. Now, an advanced version considers the underlying size-based dynamics of the targeted stocks for Danish and German vessels harvesting the North Sea and Baltic Sea fish stocks. The stochastic fishing process is specific to the vessel catching power and to the encountered population abundances, based on disaggregated research survey data. The impact of the effort displacement on the fish stocks and the vessels' economic consequences were evaluated by simulating individual choices of vessel speed, fishing grounds, and ports. Some scenarios led to increased energy efficiency and profit while others such as fishing closures or fishermen optimization sometimes lowered the revenue by altering the spatiotemporal effort allocation. On an individual scale, the simulations led to gains and losses due to either the interactions between vessels or to the alteration of individual patterns. We demonstrate that integrating the spatial activity of vessels and fish abundance dynamics allow for more realistic predictions of fishermen behaviour, profits, and stock abundance. L'effet relatif de scenarios variant l'allocation spatiale de l'effort individuel de bateaux de peche, en terme de consommation de carburants, d'efficacite energetique, de soutenabilite des captures, ou de profitabilite des pecheries est etudie par le biais d'un modele spatialement explicite et individu-centre. La version avancee du modele presentee ici considere maintenant la dynamique sous-jacente d'un certain nombre de stocks peches par les bateaux de peche danois et allemands a travers la Mer du Nord et la Mer Baltique. Le processus stochastique inclus la depletion locale des stocks specifique a chaque bateau selon sa capacite de peche propre et a l'abondance rencontree sur chaque site, utilisant des donnees issues de campagnes scientifiques en mer. Les consequences sur la mortalite des stocks et sur l'economie des bateaux sont evaluees ici a une echelle spatio-temporelle fine en simulant des alternatives quant-aux choix individuels. Certains des scenarios testes conduisent a une meilleure efficacite energetique et economique, alors que d'autres conduisent a de mauvais choix d'allocation d'effort en terme d'efficacite. A l'echelle individuelle, les simulations conduisent a des gains ou bien des pertes, s'expliquant soit par des interactions techniques entre bateaux pour les memes stocks, soit du fait de l'alteration des schemas individuels d'allocation. Nous demontrons dans cette etude qu' integrer la dimension spatio-temporelle des bateaux avec la dynamique sous-jacente des stocks de poissons permet de predire le comportement de peche, les profits et les abondances de facon plus aboutie., Introduction The growing use of incentive-based fishery management approaches (e.g., Fulton et al. 2011; Ulrich et al. 2012) calls for new generation of bio-economic multistock-multifishery models that can be used [...]

Underwater video has become an important tool for monitoring reef fish populations worldwide because it is nonextractive and not strongly selective. A variety of approaches have been developed to enumerate fish on videos, but to our knowledge these metrics have not been tested to determine if they are proportional to true abundance. We compared the mostcommonly used metric, MaxN (i.e., the maximum number of fish in a single frame during the viewing interval), to a newly developed metric, MeanCount (i.e., the mean number of fish observed in a series of snapshots over a viewing interval), using simulations, a laboratory experiment, and an empirical study. MaxN was nonlinearly related to true abundance using all three approaches, providing increasingly dampened estimates of abundance with increasing true abundance (i.e., hyperstability). Therefore, MaxN may result in positively biased indices of abundance for declining fish stocks or negatively biased abundance indices when fish stocks are increasing. Alternatively, MeanCount was generally linearly related to true abundance and its variability was similar to MaxN, suggesting that MeanCount can be useful for indexing abundance of fish in underwater video surveys. La video sous-marine est devenue un important outil pour la surveillance des populations de poissons recifaux a l'echelle planetaire en raison de son caractere non extractif et peu selectif. Si differentes approches ont ete mises au point pour denombrer les poissons dans les videos, a notre connaissance, ces methodes de mesure n'ont pas ete testees pour determiner si les resultats qu'elles donnent sont proportionnels a l'abondance reelle. Nous avons compare la mesure la plus couramment utilisee, le MaxN (c.-a-d. nombre maximum de poissons dans une image donnee durant l'intervalle de visionnement), a une mesure nouvellement mise au point, MeanCount (c.-a-d. nombre moyen de poissons observes dans une serie d'instantanes pris durant un intervalle de visionnement), a la lumiere de simulations, d'une experience en laboratoire et d'une etude empirique. MaxN etait relie de maniere non lineaire a l'abondance reelle pour les trois approches, l'attenuation des estimations de l'abondance augmentant parallelement a l'abondance reelle (c.-a- d. hypersensibilite). Ainsi, MaxN peut donner des indices d'abondance biaises positivement pour les stocks de poissons en declin, ou negativement pour les stocks de poissons en expansion. Pour sa part, MeanCount presente generalement une relation lineaire avec l'abondance reelle, et sa variabilite est semblable a celle de MaxN, ce qui porte a croire que MeanCount pourrait etre utile pour determiner l'indice d'abondance de poissons dans les evaluations reposant sur la video sous-marine. [Traduit par la Redaction], Introduction Visual census techniques have become an increasingly important tool in monitoring reef fish populations worldwide. Being inherently nonextractive, visual census techniques are often used to sample no-take areas such [...]

Abstract--Identification of the spatial scale at which marine communities are organized is critical to proper management, yet this is particularly difficult to determine for highly migratory species like sharks. We [...]

Abstract--Demographic parameters were derived from sectioned otoliths of John's Snapper (Lutjanus johnii) from 4 regions across 9° of latitude and 23° of longitude in northern Australia. Latitudinal variation in size [...]

Abstract--With the use of a baited stereo-video camera system, this study semiquantitatively defined the habitat associations of 4 species of Lutjanidae: Opakapaka (Pristipomoides filamentosus), Kalekale (P. sieboldii), Onaga (Etelis coruscans), [...]

Abstract: Marine organisms occasionally settle at exceptional densities, whereby thousands of individuals arrive concurrently. High levels of mortality, which has historically been attributed to predation or competition, often follow this [...]

With headwaters 240 km to the east (Fig. 1), the river is navigable for only the first 3 km from the sea, after which it becomes shallow, with numerous rapids [...]

The Blue Sucker, Cycleptus elongatus (Lesueur) is a long, compressed and streamlined catostomid that occurs in the Mississippi River basin from Pennsylvania to central Montana and south to Louisiana, Texas, [...]

For Gulf of Alaska (GOA) fish populations, ordination by principal component analysis of a matrix of species by early life history and ecological traits resulted in distribution of species along three primary gradients. These are synonymous with phenology of egg and larval production, quantity of production, and ubiquity of larvae, the latter representing temporal and spatial extent of distribution in the pelagic environment. GOA species were assigned to categories that shared similar positions in ordination space relative to the three primary gradients. From this comparative analysis, a conceptual framework is proposed for species' early life histories representing trade-offs in adaptation to prevailing environmental conditions and associated vulnerability and resilience factors that may modulate species' recruitment responses to environmental variability. The utility of this framework for evaluating response to environmental forcing was supported by the analysis of a 27-year time series of GOA late spring larval fish abundance. The hypothesis for this ongoing research is that we can utilize similarities in reproductive and early life history characteristics among species to identify (i) ecologically determined species groups that are predisposed to respond to environmental forcing in similar ways and (ii) plausible environmental predictors of recruitment variation attributable to aspects of early life history. Pour des populations de poissons du golfe de l'Alaska (GOA), l'ordination par analyse en composantes principales d'une matrice d'especes en fonction de caracteres ecologiques et relatifs aux premiers stades du cycle biologique a produit une distribution des especes le long de trois gradients principaux. Ces gradients correspondent a la phenologie de la production d'oeufs et de larves, a la quantite de production et a l'ubiquite des larves, cette derniere representant l'etendue temporelle et spatiale de la repartition dans le milieu pelagique. Les especes du GOA ont ete affectees a des categories occupant des positions semblables dans l'espace d'ordination relativement aux trois gradients principaux. A la lumiere de cette analyse comparative, un cadre conceptuel est presente qui decrit les premiers stades du cycle biologique des especes en terme de compromis associes a l'adaptation aux conditions ambiantes et des facteurs de vulnerabilite et de resilience connexes qui pourraient moduler des modifications au recrutement des especes decoulant de la variabilite du milieu. L'utilite de ce cadre pour evaluer la reponse a des forcages environnementaux est corroboree par l'analyse d'une serie chronologique de 27 ans de donnees sur l'abondance de larves de poissons a la fin du printemps dans le GOA. L'hypothese qui sous-tend ces travaux veut que les similitudes entre especes sur les plans des caracteres reproductifs et des premiers stades du cycle biologique puissent etre utilisees pour cerner (i) des groupes d'especes determines ecologiquement predisposes a reagir de maniere semblable a des forcages environnementaux et (ii) des predicteurs environnementaux plausibles de la variation du recrutement attribuable a differents aspects des premiers stades du cycle biologique. [Traduit par la Redaction], Introduction Understanding what regulates recruitment variability has been the number one issue in fisheries science since the early 20th century. It is one of the major sources of uncertainty in [...]

Recent analyses of historical data of fish abundance and distribution have shown the importance of a long temporal perspective in the evaluation of the current status of fish populations, but pose numerous difficulties such as fragmentation and inhomogeneities in the amount of available information in space and time. Using mixed-effects models in a multiscale analysis, we identified an appropriate spatiotemporal scale of investigation of a high-quality, spatially explicit historical data set, and we reconstructed the long-term spatial dynamics of Atlantic cod (Gadus morhua) in the Kattegat-Skagerrak along the 20th century. We identified a northern and southern main aggregation of adult cod in the study area, corresponding to the Skagerrak portion of the North Sea and the Kattegat cod stocks, respectively. The stocks showed specificities in their spatial dynamics, but common extensive loss of coastal aggregations during the last decades when only 13% (Kattegat) and 35% (Skagerrak) of the estimated early century cod biomass was left. Our reconstruction showed that the collapse of the cod stocks in the area followed the peak in landings in the 1960s-1970s, suggesting that the postwar development of the industrial fisheries played a major role in the decrease of local abundances and disappearance of local adult cod aggregations. Des analyses recentes de donnees historiques sur l'abondance et la distribution de poissons ont demontre l'importance d'une perspective temporelle a long terme dans l'evaluation de l'etat actuel des populations de poissons. Ces analyses presentent toutefois de nombreuses difficultes, telles qu'une fragmentation et une heterogeneite spatiales et temporelles de la quantite d'information disponible. En utilisant des modeles a effets mixtes dans une analyse multi-echelle, nous avons cerne une echelle spatiotemporelle convenant a l'etude d'un ensemble de donnees historiques spatialement explicites de haute qualite et reconstitue la dynamique spatiale a long terme de la morue franche (Gadus morhua) dans la region du Cattegat et du Skagerrak au cours du 20e siecle. Nous avons cerne deux grandes agregations, septentrionale et meridionale, de morues adultes dans la region a l'etude, correspondant aux stocks de la region du Skagerrak de la mer du Nord et du Cattegat, respectivement. Si les deux stocks presentaient des specificites en ce qui concerne leur dynamique spatiale, ils etaient tous deux caracterises par la disparition generalisee d'agregations cotieres durant les dernieres decennies, alors qu'il ne restait que 13 % (Cattegat) et 35 % (Skagerrak) de la biomasse de morue estimee du debut du siecle. La reconstitution a demontre que l'effondrement des stocks de morue dans la region s'est produit dans la foulee de la pointe des debarquements des annees 1960-1970, portant a croire que le developpement des peches industrielles dans l'apres-guerre a joue un role majeur dans la diminution de l'abondance locale et la disparition d'agregations locales de morues adultes. [Traduit par la Redaction], Introduction There is an increasing demand for historical baselines of marine ecosystems (Pauly 1995). This is particularly relevant for the evaluation of harvested populations and to set goals for their [...]

Ignorance of spatial structures in fisheries management may lead to unexpected risks of overexploitation. Based on the information about small yellow croaker (Larimichthys polyactis) off the coast of China, we simulated a fish population consisting of three subpopulations mixing at intermediate levels, which was considered in the 'true' spatial structure of the population in this study. Three scenarios of population spatial structure were assumed in assessing and managing this simulated fishery: (i) metapopulation, which has the same structure as the 'true' population; (ii) three independent subpopulations, which overlook the exchanges among the subpopulations; and (iii) unit population, which completely ignores the population spatial structure. Corresponding approaches were applied to assess and manage each of these assumed fish populations. The management time period was assumed to be 10 years with two harvesting levels (i.e., maximum sustainable yield (MSY) and [f.sub.0.1]) Assessing and managing the metapopulation as several independent populations could lead to a high probability of overexploitation. Managing the metapopulation as a unit population could lead to local depletion. Use of MSY as a management target may be risk prone in the existence of a metapopulation, and use of a fishing mortality lower than [f.sub.0.1] as a management target is more desirable. Ne pas tenir compte des structures spatiales dans la gestion de la peche peut mener a des risques imprevus de surexploitation. En utilisant des donnees sur la courbine jaune (Larimichthys polyactis) du large de la cote de Chine, nous avons simule une population de poissons comprenant trois sous-populations qui se melangent a des niveaux intermediaires, ce qui est considere la << veritable >> structure spatiale de la population dans notre etude. Nous avons suppose trois scenarios de structure spatiale de la population dans l'evaluation et la gestion de cette peche simulee, (i) une metapopulation qui a la meme structure que la population << veritable >>, (ii) trois sous-populations independantes, ce qui neglige les echanges entre les sous-populations et (iii) une population unitaire qui ignore completement la structure spatiale de la population. Nous avons utilise des methodes semblables pour evaluer et gerer chacune de ces populations hypothetiques de poissons. Nous avons determine une periode de gestion de 10 ans avec deux niveaux de recolte (c.-a-d. le rendement maximum durable (MSY) et [f.sub.0,1]). L'evaluation et la gestion de la metapopulation comme plusieurs populations independantes pourraient mener a une forte probabilite de surexploitation. La gestion de la metapopulation comme une population unitaire pourrait provoquer des depletions locales. L'utilisation de MSY comme cible de gestion peut entrainer des risques, s'il existe une metapopulation; l' utilisation d' une mortalite due a la peche inferieure a [f.sub.0,1] comme cible de gestion semble donc plus desirable. [Traduit par la Redaction], Introduction A metapopulation is defined as a group of subpopulations in which local subpopulation dynamics are driven in part by dispersal from other subpopulations in the group (Hanski 1999). Many [...]