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Studies investigating population structure and mixed-stock composition of fish populations frequently use otolith chemistry as a natural tool for discerning stocks. Current methods for estimating mixed-stock composition, however, assume complete accuracy in the training data, which is often not the case. Here we present a method for estimating mixed-stock composition using multivariate continuous data that accounts for uncertainty in the training data. Application of the method to previously reported data for natal homing in weakfish (Cynoscion regalis) and simulations based on these data revealed that for sample sizes greater than about 30, the present method provides results that are quite similar to those of previous methods. An advantage of this Bayesian approach over other methods, however, is the ease with which functionals of the model, such as migration distance and direction, can be calculated. It also provides simple means of visualizing spatial structure in the classification probabilities and migration patterns. Les recherches qui s'interessent a la structure de population et a la composition des stocks mixtes chez les populations de poissons utilisent souvent la chimie des otolithes comme outil naturel pour separer les stocks. Cependant, les methodes courantes pour estimer la composition des stocks assument que les donnees d'entrainement sont parfaitement ex-actes, ce qui n'est souvent pas le cas. Nous presentons ici une methode pour estimer la composition de stocks mixtes qui utilise des donnees multidimensionnelles continues qui tiennent compte de l'incertitude dans les donnees d'entrainement. L'utilisation de la methode avec des donnees publiees anterieurement sur le retour au lieu de naissance chez l'acoupa royal (Cynoscion regalis) et des simulations basees sur ces donnees montrent que, pour des echantillons superieurs a environ 30, notre methode fournit des resultats qui sont tres semblables a ceux des methodes anterieures. Un avantage de notre approche bayesienne par rapport aux autres methodes est la facilite avec laquelle on peut calculer les fonctionnelles du modele, telles que la distance et la direction de la migration. Elle procure aussi un moyen simple de visualiser la structure spatiale dans les probabilites de la classification et les patrons de migration. [Traduit par la Redaction], Introduction The chemical composition of otoliths serves as a natural tag for the investigation of population structure and connectivity in fish populations. As otolith material is deposited, trace elements and [...]

The management of Pacific salmon (Oncorhynchus spp.) populations, which are spatially distributed across thousands of waterways in coastal British Columbia, Canada, presents considerable challenges to resource managers. We evaluated the efficacy of salmon management by Fisheries and Oceans Canada (DFO) over the past 55 years in two key areas: (i) the achievement of internally generated target escapement levels and (ii) escapement monitoring. We show that less than 4% of monitored streams (n = 7 of 215), which represent a small fraction of all salmon-bearing waterways (n = 2592), have consistently met escapement targets since 1950. During this same period, the number of streams monitored by DFO has simultaneously decreased. Further, current monitoring efforts fall short of encompassing the range of salmon diversity identified within recently designated conservation units. Importantly, we found that this erosion of monitoring effort has been biased towards dropping smaller runs that failed to meet target escapements in the previous decade. We suggest that such increasingly selective monitoring is presenting a progressively more biased evaluation of population health. In addition to fostering a 'shifting baseline' syndrome, we conclude that these changes to monitoring can not provide data required for precautionary harvest management under the high exploitation levels that these runs experience. La gestion des populations de saumons du Pacifique (Oncorhynchus spp.), qui sont reparties spatialement dans des milliers de cours d'eau sur la cote de la Colombie-Britannique, presente des defis importants aux gestionnaires des ressources. Nous evaluons l'efficacite de la gestion des saumons faite par Peches et Oceans Canada (DFO) au cours des 55 dernieres annees dans deux domaines importants: (i) l'atteinte des cibles d'echappement par les processus intrinseques et (ii) la surveillance de l'echappement. Nous montrons que moins de 4 % des cours d'eau suivis (n = 7 de 215), qui representent une petite fraction des cours d'eau a saumons (n = 2592), ont regulierement atteint leurs cibles d'echappement depuis 1950. Durant la meme periode, le nombre de cours d'eau suivis par DFO a simultanement decru. De plus, les efforts de surveillance actuels n'arrivent pas a couvrir l'etendue de la diversite des saumons identifiee au sein des unites de conservation recemment definies. Ce qui est important de noter, c'est que cette erosion de l'effort de surveillance a frappe de facon disproportionnee les petits groupes de montaison qui n'ont pas reussi a atteindre leurs cibles d'echappement au cours de la derniere decennie. Nous croyons que cette surveillance de plus en plus selective fournit une evaluation toujours plus faussee de la sante des populations. En plus de produire un syndrome de << donnees de base changeantes >>, ces modifications dans la surveillance ne permettent pas d'obtenir les donnees necessaires pour une gestion prudente des recoltes dans les conditions de forte exploitation que connaissent ces groupes de montaison. [Traduit par la Redaction], Introduction Salmon management presents complex biological, economic, and political challenges (Wright 1981; Hilborn and Luedke 1987). In British Columbia (BC), resource managers rely heavily on stock assessment programs to guide [...]

Detailed avoidance reactions of adult migrating salmon to a mobile survey vessel were successfully observed with side-looking dual-frequency identification sonar (DIDSON) in the lower Fraser River (British Columbia, Canada). Both adult sockeye (Oncorhynchus nerka) and pink salmon (Oncorhynchus gorbuscha) returning to the river were found to avoid the approaching vessel by initiating lateral movements away from the vessel, making the fish unlikely to be insonified by the downward-looking transducers towed by the vessel. The vessel was found to have an estimated mean interference range of 4 m from its propeller. Analyses of the data concluded that once the vessel and fish were separated by more than 7 m, the vessel no longer affected the normal migration behaviour of the fish. Un sonar lateral d'identification a 'double frequence (DIDSON) nous a permis d'observer avec succe's les reactions detaillees d'evitement des saumons adultes en migration face a' un navire mobile d'inventaire dans le cours inferieur du Fraser (Colombie-Britannique, Canada). Tant les saumons rouges (Oncorhynchus nerka) que les saumons roses (Oncorhynchus gorbuscha) qui retournent dans la rivie're evitent le navire qui s'approche en entreprenant des deplacements lateraux pour se distancer du navire, ce qui fait que les poissons risquent peu d'etre reperes par les capteurs sonar orientes vers le bas et tires par le navire. La portee moyenne de l'interference du navire est estimee a' 4 m depuis l'helice. Les analyses de ces donnees me'nent a' la conclusion que lorsque le navire et les poissons sont separes par une distance de plus de 7 m, le navire n'affecte plus le comportement normal de migration des poissons. [Traduit par la Redaction], Introduction Vessel-based mobile acoustic survey is traditionally an effective sampling method for assessing abundance of fish stocks distributed over large areas in oceans, rivers, and lakes (McLennan and Simmonds 1992). [...]

To evaluate the stock structure of yellow perch (Perca flavescens) in the southern basin of Lake Michigan and in Green Bay, we analyzed recaptures from a lake-wide mark-recapture study implemented from 1996 to 2001 to infer the range and pattern of movement and spawning-site fidelity. Yellow perch generally moved south along the western shoreline, west along the southern shoreline, and north along the eastern shoreline during summer and non-summer months; the magnitude of movement was greater after spawning. Spawning yellow perch frequently returned to the same site, with 35%-80% of recaptured individuals returning to their marking site. Results from multiple tagging sites within Illinois indicated that spawners may return to larger areas rather than to specific sites, suggesting that large spawning complexes exist. Despite strong fidelity in some areas, straying was evident from all sites during spawning, resulting in mixing throughout the southern basin. Such mixing could promote gene flow and diminish stock differentiation. Dispersal of yellow perch within the southern basin of Lake Michigan occurred regularly across adjacent management boundaries. Therefore, adjacent jurisdictions may wish to consider re-examining their regulations based on this information to ensure consistent, complementary regulations that incorporate the movement patterns of yellow perch. Afin d'evaluer la structure du stock de perchaudes (Perca flavescens) dans le bassin sud du lac Michigan et dans Green Bay, nous avons analyse les recaptures provenant d'une etude de marquage et de recapture menee sur l'ensemble du lac en 1996-2001; nous en avons deduit l'etendue de la repartition et les patrons de deplacement, ainsi que la fidelite au site de fraye. Les perchaudes se deplacent generalement vers le sud le long de la rive ouest, vers l'ouest le long de la rive sud et vers le nord le long de la rive est durant les mois d'ete et durant les autres mois; l'amplitude des deplacements est plus grande apres la fraye. Les perchaudes en reproduction retournent souvent au meme site de fraye, 35-80% des individus recaptures etant retournes a leur site de marquage. Les resultats obtenus dans des sites multiples de marquage en Illinois indiquent que les reproducteurs peuvent retourner vers des endroits plus etendus que les sites specifiques, ce qui laisse croire qu'il existe des complexes elargis de fraye. Malgre la forte fidelite a certains regions, il y a des indications d'errance dans tous les sites durant la fraye, ce qui cause des melanges dans tout le bassin sud. Ce melange pourrait favoriser le flux genique et reduire la differenciation des stocks. Il y a une dispersion reguliere des perchaudes au sein du bassin sud entre les limites des differentes zones adjacentes de gestion. C'est pourquoi d'apres ces renseignements, les administrations adjacentes pourraient vouloir reexaminer leurs reglements afin de s'assurer d'avoir des reglementations compatibles et complementaires qui tiennent compte des deplacements des perchaudes. [Traduit par la Redaction], Introduction Stock identification and discrimination are fundamental issues in fisheries management that are used for a variety of purposes, including conservation of biodiversity, recovery of endangered species, the spatial allocation [...]

Abstract: This study summarizes US and Japanese historical North Pacific albacore (Thunnus alalunga) tagging data and uses maximum likelihood methods to estimate seasonal migration rates of young North Pacific albacore. [...]

Abstract: Several studies have shown that fish shoals may consist of closely related individuals. It has been found, for example, that released out-migrating salmon smolts tend to aggregate with kin, [...]

Abstract: Genotypic data from eight microsatellite loci are used to infer population structure, effective population size, migration rates, and patterns of allelic richness among wild and hatchery populations of Oregon [...]

Abstract: Otolith Sr:Ca ratios near primordia (Sr:[Ca.sub.Core]) have been used to distinguish progeny of resident and anadromous Oncorhynchus mykiss and to estimate rates of exchange between the two forms; however, [...]

Partial migration is a common phenomenon among many animals and occurs in many types of ecosystems. Understanding the mechanisms behind partial migration is of major importance for the understanding of population dynamics and, eventually, ecosystem processes. We studied the effects of food availability on the seasonal partial migration of cyprinid fish from a lake to connected streams during winter by the use of passive telemetry. Fish with increased access to food were found to migrate in higher proportion, earlier in the season, and to reside in the streams for a longer period compared to fish with decreased access to food. Furthermore, fewer unfed migrants returned to the lake, indicating higher overwinter mortality. Our results suggest that individual fish trade off safety from predation and access to food differently depending on their body condition, which results in a condition-dependent partial migration. Hence, our main conclusion is that individual decision-making is based on assessment of own condition which offers a mechanistic explanation to partial migration. Moreover, this may be of high importance for understanding population responses to environmental variation as well as ecosystem dynamics and stability. Key words: cyprinid fish; food availability; individual behavior; migration; partial migration; predation; roach; Rutilus rutilus.

Abstract: Herbivorous fishes show a clear latitudinal diversity gradient, making up a larger proportion of the fish species in a community in tropical waters than in temperate waters. One proposed [...]

Abstract: Spectacular long-term cycles (around 110 years), independent of human exploitation, have been seen in historical catches of Atlantic bluefin tuna (Thunnus thynnus). Previous studies indicated that such variations could [...]

Abstract: In this study, we examine the performances of current stock assessment methods with respect to their ability to (i) provide estimates of maximum sustainable yield (MSY), [F.sub.MSY], and [B.sub.MSY] [...]

Abstract: Pauly (1980. J. Cons. Int. Explor. Mer, 39: 175-192) showed that natural mortality rates in fish could be predicted from body growth parameters and environmental temperature but found no [...]

The migration of large aggregations of animals that sweep through the landscape is a phenomenon with large consequences in many ecosystems. It has been suggested that such migrations are mediated by resource depletion. Under this hypothesis it has been shown that simple foraging rules may generate density-dependent migratory waves (DDMW) in which the speed and amplitude increase with animal abundance. We tested these predictions on a 32-year data set of the spatial distribution of the two youngest age groups of a small pelagic schooling fish, the capelin (Mallotus villosus), by the end of their annual feeding migration in the Barents Sea. Our data suggest that the two age groups divided the Barents Sea by forming migratory waves that moved in opposite directions. The aggregation and spatial displacement of these waves increased with increasing age-specific abundance. However, possibly through social interactions, migratory pattern was modified by the abundance of the other age group. Key words: animal movement; area-restricted search; Barents Sea; capelin; gregarious behavior; Mallotus villosus; migration; pelagic schooling fish; spatial distribution.

Abstract: Otolith microchemistry and isotopic analyses have emerged as effective techniques for providing insights into fish environmental history that are difficult to obtain by other means. Stable hydrogen isotope ratio [...]

Abstract: Beginning in 1995, segments of the late-run sockeye salmon (Oncorhynchus nerka) stocks from the Fraser River, British Columbia, have initiated upriver spawning migration up to 6 weeks earlier than [...]

Various predator--prey, host--pathogen, and competitive interactions can combine to cause density dependence in population growth. Despite this possibility, most empirical tests for density-dependent interactions have focused on single mechanisms. Here we tested the hypothesis that two mechanisms of density dependence, parasitism and a shortage of refuges, jointly influence the strength of density-dependent mortality. We used mark--recapture analysis to estimate mortality of the host species, the bridled goby (Coryphopterus glaucofraenum). Sixty-three marked gobies were infected with a copepod gill parasite (Pharodes tortugensis), and 188 were uninfected. We used the spatial scale at which gobies were clustered naturally (~4 [m.sup.2]) as an ecologically relevant neighborhood and measured goby density and the availability of refuges from predators within each goby's neighborhood. Goby survival generally declined with increasing density, and this decline was steeper for gobies with access to few refuges than for gobies in neighborhoods where refuges were common. The negative effects of high density and refuge shortage were also more severe for parasitized gobies than for gobies free of parasites. This parasite has characteristics typical of emerging diseases and appears to have altered the strength of a preexisting density-dependent interaction. Key words: bridled goby; competition, coral reefs; Coryphopterus glaucofraenum; density dependence; emerging diseases; fishes; mark--recapture; mortality; parasites;predation; refuges.

Freshwater fish assemblages are sensitive to changes in land use, but it is unclear how rapidly assemblages respond to such change or how closely they track physical changes in the stream environment. We monitored fish assemblages at the outflow of three watersheds on the outer coastal plain of Mississippi over a period of 8 y. The watersheds differed in patterns of land use, being predominantly forested, rapidly urbanizing, and long-urbanized, respectively. Watersheds were distinct in fish species composition, differing primarily in abundance of Etheostoma lynceum, E. stigmaeum, Luxilus chrysocephalus and Lythrurus roseipinnis. Species richness was consistently greatest at the predominantly forested site and least at the urbanized site. Fish assemblages were distinguishable in terms of substrate preference, water-speed, silt tolerance, and trophic habit. The stream draining the urbanizing watershed showed an increase in richness of species of high silt tolerance and a decrease in richness of those preferring a gravel substrate over the sampling period. Contrary to expectation, annual variation in composition was modest relative to differences among sites. Annual variation in richness and numbers was unrelated to measures of streamflow or seasonal precipitation. Changes in stream character related to land use change appear to have impacted the fish assemblages of these streams, but the transition to an urban fish assemblage in the urbanizing stream occurred before the study period, well before the obvious signs of physical degradation appeared at the site.

In demersal fish species with a pelagic larval stage, settlement patterns may be a consequence of variations in larval supply, habitat selection at settlement, and processes acting between the time of settlement and the time of benthic sampling. This study describes temporal (1994-1998) and spatial variation in plaice (Pleuronectes platessa L.) settlement densities in four semi-isolated nursery areas with similar habitat characteristics, in the non-tidal Gullmarsfjord on the west coast of Sweden. Juvenile abundance varied by a factor of ten, both among years and among nursery grounds. For the 3 years when larval sampling was undertaken (1994-1996) and all nursery areas, there was a significant positive relationship between larval supply and juvenile abundance (linear regression: [r.sup.2] = 0.45, n = 24, P < 0.001). On the southern side of the fjord, a significant positive relationship between larval and juvenile abundance was found in one area ([r.sup.2] = 0.62, n = 6, P < 0.05). The absolute mortality rate of plaice after settlement was related to the initial settlement density ([r.sup.2] = 0.95, n = 20, P < 0.001), and to the abundance of predatory shrimps Crangon crangon ([r.sup.2] = 0.44, n = 20, P < 0.01). Plaice otoliths were found in 6% of the shrimp stomachs analysed from an area with high density (13.3 [m.sup.-2]) of newly settled plaice. The present study suggests that the density of juvenile plaice was limited by larval supply to the nursery grounds. Consistency in the relative abundance of juveniles among nursery grounds between years also suggested that some nursery areas may be in the settlement shadow of others. The irregular nature of the coastline in combination with larval depletion could thereby cause small-scale ([10.sup.3]-[10.sup.4] m) variation in settlement densities of the same order of magnitude as the inter-annual variability in recruitment to individual nursery grounds.

Research has been conducted on the light and large traps deployed to investigate the composition and size-frequency distribution of fishes off the coast of Western Australia in two sampling programs. Results indicate that the cross-shelf patterns in fish and invertebrate catches have been mapped equally well by both trap designs.

Research has been conducted on the fish assemblage inhabiting the littoral rocky reef. The spatial pattern of this assemblage has been investigated in relation with its habitat via the spatial and regression analysis techniques and the results indicate that the habitat heterogeneity of the rocky substrate promotes the species richness.

Abstract. -- The aquatic habitats of the Keechi Creek Wildlife Management Area in central east Texas were surveyed in May, June and August of 1999. A total of 34 species [...]

The spatial, diel and tidal variability in the abundance of piscivorous fishes and their teleost prey, and the dietary composition of predatory fishes were investigated in beds of Heterozostera tasmanica within Port Phillip Bay, Australia, from September 1997 to February 1998. Predatory and prey fish assemblages were sampled from beds of H. tasmanica at three locations during each combination of diel (day and night) and tidal (high and low) cycles. Pelagic and benthic crustaceans represented >60% by abundance of the diets of all predatory fishes. Seven species, 54% of all predatory fishes, were piscivorous. These piscivores consumed individuals from seven families, 36.8% of the fish families being associated with seagrass. Western Australian salmon, Arripis truttacea (Arripidae) (n = 174) and yank flathead, Platycephalus speculator (Platycephalidae) (n = 46) were the most abundant piscivores. A. truttacea consumed larval/post-larval atherinids, gobiids and sillaginids. P. speculator consumed late-juvenile/adult atherinids, clinids and gobiids. While the abundances of piscivores varied between locations (P < 0.001) and diel periods (P = 0.028), the relative differences in piscivore abundance between sites and diel periods were not consistent between tides. The abundances of A. truttacea varied in a complex way amongst sites, diel period and tidal cycle, as shown by a three-way interaction between these factors (P = 0.026). Only during diurnal periods at St. Leonards was the abundance of A. truttacea significantly higher during high than low tides (P < 0.001). During the other diel periods at each site, the abundance of A. truttacea did not vary. P. speculator was significantly more abundant nocturnally (P = 0.017). The abundance of small (prey) fishes varied significantly amongst sites (P < 0.001). During the day, the abundance of small fishes did not vary between high and low tides (P = 0.185), but their nocturnal abundance was greater during low tide (P < 0.001). Atherinids (n = 1732) and sillaginids (n = 1623) were the most abundant families of small fishes. Atherinids were significantly more abundant nocturnally (P = 0.005) and during low tides (P = 0.029), and varied significantly amongst sites (P < 0.001). Sillaginids varied significantly only amongst sites (P < 0.001). Seagrass beds provide a foraging habitat for a diverse assemblage of predatory fishes, many of which are piscivorous. Anti-predator behaviour and amongst-location variability in abundances of piscivorous fishes may explain some of the diel and tidal, and broad-scale spatial patterns in small-fish abundances.

Pairs of predator-approaching mosquito fish, Gambusia affinis, exhibit only a spurious occurrence of the Tit for Tat game strategy. The fish engage in an inertial motion pattern and move closer to a visible predator when a mirror is oriented parallel to their travel direction. The patterns of pair-wise motion reflect a simultaneous by-product mutualism approach of independent orientation to a predator and attraction to a companion. The mutually cooperative joint predator approach only superficially resembles the characteristics of the Tit for Tat strategy.

The number of fish species, total number of fishes, biomass and diversity is higher in the seagrasses of the Negombo Estuary, Sri Lanka, than in the mangroves. The number of species positively correlates with salinity levels and oxygen, and inversely relates to water temperature. The main stomach content of the fish of the family Syngnathidae is mangrove litter. Sea grasses form < 25% of the gut content in the juvenile species. The number of species in the estuary increases during low rainfall.

The green fluorescent fusion proteins in zebrafish are efficient modes of guiding the formation of heterologous proteins. A glutathione S-transferase/ green fluorescent fusion protein system is constructed to detect the utility of the fluorescent protein as a live staining method in zebrafish. Green fluorescence is observed for about 4 days in the zebrafish embryos.

The sensitivity of the reconstructed tracer fields to the distribution of the pseudo-oceanographic sampling strategy, essentially an antenna problem, and to errors in the velocity field and the observations are explored. The algorithm was applied to observations of silver hake eggs and larvae obtained in August 1998 on the Scotian Shelf and the evolution of fish eggs and larvae concentration was found.

We report an observation of a Marsh Wren (Cistothorus palustris) eating a small fish. On 29 November 2008, a Marsh Wren was observed catching and consuming a small fish, probably a mosquitofish (Gambusia affinis), in a coastal marsh in Jefferson County, Texas. Marsh Wrens are known to eat invertebrates, primarily insects and spiders, and we believe this is the first record of a Marsh Wren capturing and consuming vertebrate prey. Received 24 August 2009. Accepted 22 January 2010., The Marsh Wren (Cistothorus palustris) is a small passerine that inhabits a variety of coastal and interior marshland habitats. Prior observations of the feeding habits of Marsh Wrens indicate they [...]