A state-space stock assessment model for northern cod, including under-reported catches and variable natural mortality rates

Cadigan, Noel G.

doi:10.1139/cjfas-2015-0047

Cited by 99 publications

(61 citation statements)

References 39 publications

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“…It is also possible that immigration of fish occurred, most likely from Smith Sound. The sudden and not easily explained increases in both the DFO fall trawl survey (Cadigan 2016) and the present acoustic-trawl spring survey in 2008 with apparent decreases in mortality of ages 4-to 6-year-old cod occurred at the same time the Smith Sound cod were dispersing (Rose et al 2011;Cadigan 2016). Although no appropriate year-class data are available from Smith Sound for the early 2000s, it is plausible that these were relatively strong, because the 1990 and 1992 founder year-classes were abundant with substantial spawning potential in those years (Rose 2003).…”

Section: Discussionmentioning

confidence: 98%

“…Indeed, both the fall trawl survey of (the Department of) Fisheries and Oceans Canada (DFO) and the winter acoustictrawl survey reported here showed an increase in cod biomass in the Bonavista Corridor that was difficult to explain by local production alone. Recently, a modelling study examined that disparity by including acoustic-trawl survey data from Smith Sound and an assumption that maturing fish regrouped with the Bonavista Corridor cod after 2007 (Cadigan 2016). In effect, doing so changed the catchability (q) of the main DFO trawl survey over time, with a model that fit most existing data better and further suggested that northern cod spawning biomass may have been underestimated in recent years based on the fall trawl survey alone.…”

Section: Introductionmentioning

confidence: 99%

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Northern cod comeback

Rose

Rowe

2015

Can. J. Fish. Aquat. Sci.

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Abstract: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.Résumé : 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-rétablissement présumé de poissons marins, fait un grand retour après presque deux décennies d'attrition et de moratoire sur la pêche. À partir de relevés acoustiques et au chalut des principaux composants pré-reproducteurs et reproducteurs du stock, nous démontrons que la biomasse a augmenté de quelques dizaines de milliers de tonnes à >200 000 tonnes durant la dernière décennie. Cette augmentation a été signalée par le comportement de rassemblement massif en bancs à la fin de l'hiver, d'abord observé en 2008 dans la partie sud de l'aire de répartition du stock (corridor de Bonavista) après une absence de 15 ans, qui a peut-être été favorisé par l'immigration. Des augmentations de la taille et de l'embonpoint des poissons et des diminutions apparentes de la mortalité ont suivi, menant à 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 été observées pour la première fois depuis le moratoire dans les groupes reproducteurs plus septentrionaux de ce complexe de stocks. Ce rebond de la morue a accompagné des augmentations de l'abondance du capelan (Mallotus villosus), qui avait diminué rapidement durant la période froide du début des années 1990, mais qui a récemment augmenté pendant une période de températures océaniques plus chaudes. La croissance contin...

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Section: Discussionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Northern cod comeback

Rose

Rowe

2015

Can. J. Fish. Aquat. Sci.

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“…AIC was used to determined the optimal observational likelihood, since the AIC estimates the Kullback-Liebler divergence between the candidate model and the true data generating system (Akaike 1974), i.e. the information lost by using the candidate model instead of the true data generating system (Burnham and Anderson 2002). The Kullback-Liebler divergence can not be used directly because the calculation requires full knowledge of the true data generating system.…”

Section: Discussionmentioning

confidence: 99%

Choosing the observational likelihood in state-space stock assessment models

Albertsen

Nielsen

Thygesen

2017

Can. J. Fish. Aquat. Sci.

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Data used in stock assessment models result from combinations of biological, ecological, fishery, and sampling processes. Since different types of errors propagate through these processes it can be difficult to identify a particular family of distributions for modelling errors on observations a priori. By implementing several observational likelihoods, modelling both numbers-and proportions-at-age, in an age based state-space stock assessment model, we compare the model fit for each choice of likelihood along with the implications for spawning stock biomass and average fishing mortality. We propose using AIC intervals based on fitting the full observational model for comparing different observational likelihoods. Using data from four stocks, we show that the model fit is improved by modelling the correlation of observations within years. However, the best choice of observational likelihood differs for different stocks, and the choice is important for the short-term conclusions drawn from the assessment model; in particular, the choice can influence total allowable catch advise based on reference points.

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“…The number of tags returned reflect exploitation on the tagged population whose size is known or can be estimated, whereas the size of the fishery catch reflects exploitation on a population of unknown size. Tagging experiments can provide important information on fishing and natural mortality rates that are difficult to estimate using standard catch and survey data used in fish stock assessment (Polacheck et al 2006;Cadigan 2015;Goethel et al 2015).…”

Section: Discussionmentioning

confidence: 99%

“…DFO 2013, 2015aCadigan 2015). Results of these tagging studies are reported annually in stock assessments.…”

Section: Introductionmentioning

confidence: 99%

Modelling temporal and spatial variability in tag reporting-rates for Newfoundland cod (Gadus morhua)

2016

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Mark-recapture experiments can be used to estimate the exploitation rate of a fishery; however, the estimate is influenced by the tag reporting-rate by the fishers. We present two methods to estimate the reporting rates in high/low reward ($100 and $10 CAD respectively) long-term cod tagging experiments. We fit two binomial logistic mixed-effect models, one with temporal auto-correlation in the reporting-rate yeareffects and one with independent year-effects. We estimate reporting-rates separately for recreational and commercial fishers, and test for spatial variation using fixed-effects for spatial regions. Due to the complexity of the fishery, our models account for factors such as recapture-fishery type, fish-size and time-at-liberty. Our results indicate that the recreational fishers reporting-rate was constant at 0.51 across all regions and years. The commercial fishery showed more spatial and temporal variation, with the reportingrates estimates lying between 0.67 and 0.87 for the independent year-effect model, and between 0.57 and 0.84 for the random walk model. Furthermore, we assessed the Handling Editor: Bryan F. J. Manly.The work of Konrad and Cadigan was supported by a Research and Development Corporation (RDC) of Newfoundland and Labrador Grant to N. Cadigan. We thank the technical staff of DFO Science NL Region for tagging and releasing cod, and numerous fish harvesters for providing recapture information. Electronic supplementary material The online version of this article (123 Environ Ecol Stat model performance as well as the coverage probability of nominal 95 % confidence intervals using simulations. We found that the models performed adequately; however, the nominal 95 % confidence intervals tended to be too narrow.

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A state-space stock assessment model for northern cod, including under-reported catches and variable natural mortality rates

Cited by 99 publications

References 39 publications

Northern cod comeback

Northern cod comeback

Choosing the observational likelihood in state-space stock assessment models

Modelling temporal and spatial variability in tag reporting-rates for Newfoundland cod (Gadus morhua)

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