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Redfish (Sebastes spp.) in the Northwest Atlantic (NWA) extend from Baffin Island in the north to the Gulf of Maine in the south. The two most abundant species are Sebastes mentella and Sebastes fasciatus, which are morphometrically similar and difficult to visually distinguish. Redfish are long-lived, slow-growing, late-maturing, tend to produce large year classes episodically, and have complex population structure. Intraspecific genetic groups are abundant in the NWA. They are often semipelagic and patchily distributed, which makes them difficult to survey. These are all characteristics that cause difficulties for stock assessment and for sustainable fisheries management. This was the focus of The Ocean Frontier Institute Northwest Atlantic Redfish Symposium in 2018. In this paper, we synthesize the information known about NWA redfish. To improve the scientific basis for sustainable harvest strategies, key research recommendations involve (1) improved biological sampling including species and ecotype; (2) developing integrated stock assessment models; (3) developing harvest strategies with management reference points that are appropriate for redfish; (4) improving fishing technology and practices to avoid capture of small nonmarketable redfish and other species. Les sebastes (Sebastes spp.) dans l'Atlantique Nord-Ouest (ANO) sont presents de l'ile de Baffin au Nord jusqu'au golfe du Maine au Sud. Les deux especes les plus abondantes sont Sebastes mentella et Sebastes fasciatus, semblables sur le plan morphometrique et difficiles a distinguer visuellement. Les sebastes vivent longtemps, croissent lentement, maturent tardivement, ont tendance a produire episodiquement de grandes classes d'age, et la structure de leurs populations est complexe. Des groupes genetiques intraspecifiques sont abondants dans l'ANO. Ils sont souvent semi-pelagiques et ont une repartition parcellaire, ce qui rend leur recensement difficile. Toutes ces caracteristiques sont cause de difficultes pour l'evaluation des stocks et pour la gestion durable des peches et elles constituaient le theme central du symposium sur les sebastes de l'Atlantique Nord-Ouest de 2018 de l'Ocean Frontier Institute. Nous presentons une synthese de l'information connue sur les sebastes de l'ANO. Afin d'ameliorer les fondements scientifiques de strategies de recolte durables, les principales recommandations concernant la recherche comprennent (1) l'amelioration de l'echantillonnage biologique, notamment en ce qui concerne l'espece et l'ecotype, (2) l'elaboration de modeles integres d'evaluation des stocks, (3) l'elaboration de strategies de recolte qui integrent des points de reference de gestion adaptes aux sebastes et (4) l'amelioration des technologies et pratiques de peche pour eviter la prise de sebastes et poissons d'autres especes trop petits pour etre commercialisables. [Traduit par la Redaction], 1. Introduction Redfish (Sebastes spp.) are members of the Scorpaenidae family of bony fishes that are commonly found in waters of the North Pacific and North Atlantic. In the Northwest [...]

An age-structured, spatial survey-based assessment model (SSURBA) is developed and applied to the Grand Banks stock (NAFO Divisions 3LNO) of American plaice (Hippoglossoides platessoides) in Newfoundland and Labrador. The state-space model is fit to annual spatial (i.e., three divisions) stock size-at-age research vessel (RV) survey indices that are assumed to be proportional to abundance. We model index catchability (q) as a logistic function of fish length, which varies with age, cohort, and the time of the survey; therefore, the model facilitates the estimation of q values that change spatially and temporally following changes in fish growth and survey gears. The SSURBA model produces division-level estimates of fishing mortality rates (F), stock productivity, and stock size relative to the logistic catchability assumption with q = 1 for fully selected ages. The spatial model allows us to include additional survey information compared with the space-aggregated assessment model (all of 3LNO) that is currently used to assess stock status. The model can provide estimates of relative catch, which we compare with reported catch trends to partially validate the model. Un modele devaluation base sur des releves spatiaux structures par age (SSURBA) est mis au point et utilise pour le stock des Grands Bancs (divisions 3LNO de l'OPANO) de plies canadiennes (Hippoglossoidesplatessoides) a Terre-Neuve-et- Labrador. Le modele d'espace d'etats est cale sur des indices de releves par navire de recherche (NR) de l'age selon la taille du stock qui sont presumes proportionnels a l'abondance. Nous modelisons la capturabilite indexee (q) en tant que fonction logistique de la longueur des poissons, qui varie selon l'age, la cohorte et le moment du releve; ainsi le modele facilite l'estimation de q qui varient dans l'espace et le temps a la suite de changements de la croissance des poissons et des engins utilises pour les releves. Le modele SSURBA produit des estimations au niveau de la division des taux de mortalite par peche (F), de la productivite du stock et de la taille du stock au vu de l'hypothese de capturabilite logistique pour q = 1 pour des ages entierement selectionnes. Le modele spatial nous permet d'inclure plus d'information tiree des releves que ce que permet le modele devaluation spatialement regroupe (ensemble des 3LNO) actuellement utilise pour evaluer l'etat du stock. Le modele peut fournir des estimations des prises relatives que nous comparons aux tendances des prises rapportees afin de valider partiellement le modele. [Traduit par la Redaction], Introduction Canadian fisheries management has a long history of conducting scientific surveys to monitor fish populations, with some of the earliest surveys dating back to the 1970s (Halliday and Fanning [...]

Juvenile mortality is an important factor affecting the spatiotemporal dynamics of fish recruitment, but estimation of the spatiotemporal variations in juvenile mortality rates remains challenging. We developed a state-space metapopulation dynamics model to simultaneously estimate spatiotemporal variations in juvenile mortality rates and cohort strength and applied this general modelling framework to data from multiple surveys for juvenile (ages 2-5) Atlantic cod (Gadus morhua) stocks off Newfoundland and Labrador (NL). We found large-scale synchronized dynamics of decreasing juvenile mortality rates and increasing cohort strength from offshore surveys off eastern and southeastern NL, suggesting improving reproduction and survival rates for juvenile cod. No synchronized patterns of juvenile mortality rates and cohort strength were detected for cod stocks off southern and western NL, indicating more complex cod population spatial structures in those areas. Our study demonstrates the potential of juvenile mortality to cause temporally variable and spatially synchronized dynamics of fish recruitment, and the spatial patterns of juvenile mortality and cohort strength indicate some potential mismatch between cod population structure and current management units off NL. Si la mortalite juvenile est un important facteur agissant sur la dynamique spatiotemporelle du recrutement de poissons, l'estimation des variations spatiotemporelles des taux de mortalite juvenile demeure difficile. Nous avons mis au point un modele d'espace d'etats de la dynamique de la metapopulation pour estimer simultanement les variations spatiotemporelles des taux de mortalite juvenile et de l'abondance des cohortes et avons applique ce cadre de modelisation general aux donnees de plusieurs evaluations portant sur des stocks de morues (Gadus morhua) juveniles (de 2 a 5 ans) au large de Terre- Neuve-etLabrador (T.-N.-L.). Nous relevons une dynamique synchronisee a grande echelle de diminution des taux de mortalite juvenile et d'augmentation de l'abondance des cohortes pour les evaluations au large de l'est et du sud-est de T.-N.-L., ce qui indiquerait une amelioration de la reproduction et des taux de survie des morues juveniles. Aucun motif synchronise des taux de mortalite juvenile et de l'abondance des cohortes n'est decele pour les stocks de morues au large du sud et de l'ouest de T.-N.- L., ce qui temoigne de structures spatiales plus complexes des populations de morues dans ces secteurs. L'etude demontre que la mortalite juvenile pourrait causer une dynamique variable dans le temps et synchronisee dans l'espace du recrutement de poissons, et les motifs spatiaux de mortalite juvenile et d'abondance des cohortes indiquent un mesappariement potentiel entre la structure des populations de morues et les unites de gestion actuelles au large de T.-N.-L. [Traduit par la Redaction], Introduction Two intriguing patterns of fish recruitment are strong temporal variation and large-scale spatial synchronization (e.g., Myers et al. 1997; Houde 2008), and understanding the spatiotemporal dynamics of fish recruitment [...]

Response-selective stratified sampling (RSSS) has been well studied in the statistical literature; however, the application of the resulting statistical theories and methods to a specific case of RSSS in fisheries studies, namely length- stratified age sampling (LSAS), is inadequate. We review nine estimation approaches for RSSS found in the statistical and fisheries science literature in terms of three sampling components: the first phase length composition sample, the second phase age composition sample, and the sampling scheme. We compare the performance in terms of RRMSE (relative root mean squared error) for von Bertalanffy (vonB) growth model parameter estimation using an extensive simulation study. We further demonstrate methods by applying the two best-performing and the most popular methods to estimate the vonB model parameters for American plaice (Hippoglossoides platessoides) in NAFO Divisions 3LNO. Our simulations demonstrated that mis-specifying one or more of the three sampling components increases the RRMSEs, and this effect is magnified when the age distribution is incorrectly specified. The optimal approach for data based on LSAS is the empirical proportion approach, and we recommend this method for growth parameter estimation based on LSAS data. L'echantillonnage stratifie a selectivity basee sur la reponse (ESSR) est un sujet bien etudie dans la documentation statistique, mais l'application des theories et methodes statistiques en decoulant a un cas precis d'ESSR dans les etudes sur les peches, a savoir l'echantillonnage d'ages stratifie selon la longueur (EASL), est inadequate. Nous passons en revue neuf approches d'estimation pour l'ESSR relevees dans la documentation statistique et sur les sciences halieutiques au vu de trois composants de l'echantillonnage, soit l'echantillon de la composition des longueurs de la premiere phase, l'echantillon de la composition des ages de la deuxieme phase et le plan d'echantillonnage. Nous en comparons la performance a la lumiere de l'erreur quadratique moyenne relative (EQMR) pour l'estimation des parametres du modele de croissance de von Bertalanffy (vonB) en utilisant une vaste etude de simulation. Nous faisons en outre la demonstration de methodes en appliquant les deux methodes les plus performantes et les methodes les plus populaires pour estimer les parametres du modele vonB pour la plie canadienne (Hippoglossoides platessoides) dans les divisions 3LNO de l'OPANO. Nos simulations demontrent que la definition erronee d'au moins un des trois composants de l'echantillonnage accroit les EQMR, et cet effet est amplifie si la repartition des ages est definie incorrectement. L'approche optimale pour des donnees basees sur l'EASL est l'approche des proportions empiriques, et nous recommandons cette methode pour l'estimation des parametres de croissance basee sur des donnees d'EASL. [Traduit par la Redaction], Introduction Modeling and estimation of the relationship between fish length and age (i.e., growth) is an important component of fisheries science. Growth models are used in many ways, including the [...]

Despite continued calls for the application of ecosystem‐based fisheries management, tactical fisheries management continues to be heavily reliant on single‐species stock assessments. These stock assessments rarely quantitatively integrate the effects of ecosystem processes on fish stock productivity. This lack of integration is ultimately driven by the complexity of interactions between populations, ecosystems and fisheries, which produces uncertainty when defining which processes to include and how to include them. Models developed using a structured hypothesis testing framework would allow formalizing uncertainties while underscoring the importance of incorporating different population and ecosystem processes to explain non‐stationary stock productivity. Here, we develop a conceptual framework for extending and comparing population dynamics models of increasing complexity. We illustrate the utility of the framework by investigating the population and ecosystem processes that most likely affected the differential recovery of two flatfish populations (American plaice and yellowtail flounder) on the Newfoundland Grand Banks over the past three decades. We found that yellowtail flounder population dynamics were primarily driven by recruitment variability, which was negatively affected by warmer climatological conditions, as indicated by an integrated regional climate index. Meanwhile, American plaice population dynamics were affected by a combination of temporal variability in recruitment and natural mortality, where natural mortality increased during colder than average conditions. By exploring hypotheses about the effects of population and ecosystem processes on population dynamics, this modelling framework will improve understanding about the drivers of shifts in population productivity while serving as a transparent and robust approach to support ecosystem‐based fisheries management. [ABSTRACT FROM AUTHOR]

We develop a high-resolution spatiotemporal model of stock size and harvest rates for snow crab (Chionoecetes opilio) in the southern Gulf of St. Lawrence, which supports an economically important fishery off the east coast of Canada. It is a spatial and weekly model during 1997-2014 that utilizes within-season depletion based on catch per unit of effort (CPUE; kg x [pot.sup.-1]) and also biomass values from a survey designed specifically for this stock. The model is formulated in a state-space framework. The main contribution of the model is to provide a better understanding of fishery-dependent factors that affect CPUE. There is strong evidence of density dependence in the relationship with CPUE and stock biomass, in addition to a general increase in CPUE catchability over time that may be related to changes in gear soak time and spatial variation in catchability. We also find that a natural mortality rate of 0.4 provides a better fit to survey results. Model results suggest that there is no evidence of effort saturation in the fishery. Nous developpons un modele spatiotemporel de haute resolution de la taille du stock et des taux d'exploitation pour le crabe des neiges (Chionoecetes opilio) dans le sud du golfe Saint-Laurent, qui supporte une peche d'importance economique au large de la cote est du Canada. Il s'agit d'un modele spatial et hebdomadaire pour la periode de 1997 a 2014 qui utilise l'appauvrissement durant la saison etabli a partir de la capture par unite d'effort (CPUE; kg x [cage.sup.-1]), ainsi que des valeurs de biomasse decoulant d'une campagne devaluation conque specialement pour ce stock. Le modele est formule dans un cadre d'espace d'etats. La principale contribution du modele est qu'il offre une meilleure comprehension des facteurs dependants de la peche qui ont une incidence sur la CPUE. Il y a de fortes indications d'une dependance de la densite dans la relation avec la CPUE et la biomasse du stock, en plus d'une augmentation generale de la capturabilite de la CPUE au fil du temps qui pourrait etre reliee a des modifications des temps de mouillage des engins et a des variations spatiales de la capturabilite. Nous constatons egalement qu'un taux de mortalite naturelle de 0,4 produit un meilleur calage sur les resultats de revaluation. Les resultats du modele portent a croire qu'il n'y a pas de signe de saturation de l'effort dans cette peche. [Traduit par la Redaction], Introduction Snow crab (Chionoecetes opilio) have been fished commercially in the southern Gulf of St. Lawrence (sGSL; Figs. 1 and 2) since the mid-1960s using baited traps (i.e., pots). Monitoring [...]

A basic objective of most trawl surveys is to estimate average fish density and account for uncertainty in the estimation. This is of increasing relevance because of the desire to better reflect uncertainty about stock status in fisheries management decisions. I develop score-statistic confidence intervals based on the common stratum area-weighted average estimator for stock abundance based on catches from stratified-random bottom trawl surveys and on the assumption that variation in survey catches is negative binomial in form. These confidence intervals cover only positive values and have improved coverage accuracy compared with standard-t or bootstrap intervals that are commonly used for this type of data. Methods are applied to six case studies, and simulations based on these case studies are used to evaluate the accuracy of the confidence intervals. Un des objectifs de base de la plupart des inventaires au chalut est d'estimer la densite moyenne des poissons, tout en tenant compte de l'incertitude associee a cette estimation. Cela devient de plus en plus pertinent a cause de la volonte de mieux representer l'incertitude entourant le statut des stocks dans les decisions de gestion des peches. Ce travail determine des intervalles de confiance fondes sur des statistiques de score et bases sur l'estimateur courant de la moyenne ponderee par la superficie de l'abondance des stocks d'apres des recoltes d'inventaires stratifies-aleatoires au chalut de fond; on assume que la variation dans les captures d'inventaire est de forme binomiale negative. Ces intervalles de confiance couvrent seulement les valeurs positives et possedent une precision de couverture amelioree par comparaison aux intervalles t-standard et bootstrap couramment utilises pour ces types de donnees. Nous utilisons ces methodes dans six etudes de cas et des simulations basees sur ces etudes de cas afin d' evaluer la precision des intervalles de confiance. [Traduit par la Redaction], Introduction Bottom trawl research surveys provide important information for the assessment and management of many fish stocks worldwide (e.g., Gunderson 1993; Kimura and Somerton 2006). The sampling unit is the [...]

Abstract--Paired-tow calibration studies provide information on changes in survey catchability that may occur because of some necessary change in protocols (e.g., change in vessel or vessel gear) in a fish [...]

Abstract: It is important to have good estimates of tag reporting rates when inferring exploitation rates and other mortality rates from tagging experiments. We estimate the reporting rates of single- [...]

The current stock assessment model for American plaice (Hippoglossoides platessoides) on the Grand Bank of Newfoundland (NAFO Divisions 3LNO) is a virtual population analysis (VPA). This model does not account for the considerable uncertainty about the landings data for this stock. Retrospective patterns have also been noted in the current assessment with overestimation of spawning stock biomass (SSB) and underestimation of fishing mortality (F). Via a thorough model selection process, we develop a state-space stock assessment model (SSM) for this stock that accounts for the uncertainties in the landings data and reduces the retrospective patterns. Our SSM fit the data well, with overall trends in SSB and average F (ages 9--14) similar to those estimated from the current VPA. The retrospective patterns for the SSM were reduced for both SSB and average F which should lead to the provision of better scientific advice for the management of this stock. An important result from our analysis suggests that the current assumption for natural mortality (M) in the stock assessment model may be too low. The lack of recovery of the stock of American plaice on the Grand Bank has often been attributed to overfishing, however fixing M within the model to be lower than is reasonable may be over-estimating the relative impact of F and subsequently over-stating the contribution of fishing mortality to the lack of recovery of the stock. [ABSTRACT FROM AUTHOR]

Northwest Atlantic (NWA) redfish (Sebastes mentella and Sebastes fasciatus) stocks are currently assessed using survey indicators and ageaggregated production models rather than age-based models because routine age readings are not available due to the difficulty in obtaining reliable measurements for these fish. However, recruitment is highly variable for redfish species so age-aggregated production models are not a good approach to provide short-term harvest advice. Recently a relatively large dataset of validated age readings was published that provide a good basis to model growth and its variability [i.e. population growth curve (PGC)]. In this article we propose a hierarchical random effects growth model that includes between-individual variation to estimate PGCs for 10 NWA redfish stocks and for males and females separately. These growth curves are required to develop age-based stock assessment models. External estimates of measurement error in length and age are included in our model to separate these sources of variation from the PGC variability. The hierarchical approach leads to more realistic growth curves than if each stock and sex are modelled separately. Model results indicated that S. mentella usually grow to larger sizes than S. fasciatus and that females of both these species grow to larger sizes than males. There was little evidence of a change in growth rates over time. [ABSTRACT FROM AUTHOR]