Role of predation by harp seals Pagophilus groenlandicus in the collapse and non-recovery of northern Gulf of St. Lawrence cod Gadus morhua

Chassot, Emmanuel; Duplisea, Daniel E.; Hammill, Mike O.; Caskenette, Amanda; Bousquet, Nicolás; Lambert, Yvan; Stenson, Garry B.

doi:10.3354/meps07897

Cited by 21 publications

(21 citation statements)

References 54 publications

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“…Increases in natural mortality rate due to seals have been hypothesized to prevent recovery of some Atlantic cod stocks (Chassot et al 2009), while high fishing pressure has been implicated in other stocks (Cardinale and Svedang 2004). The latter can occur even when the catch amounts are low (Shelton et al 2006).…”

Section: Discussionmentioning

confidence: 99%

In what direction should the fishing mortality target change when natural mortality increases within an assessment?

Legault

Palmer

2016

Can. J. Fish. Aquat. Sci.

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Traditionally, the natural mortality rate (M) in a stock assessment is assumed to be constant. When M increases within an assessment, the question arises how to change the fishing mortality rate target (F Target ). Per recruit considerations lead to an increase in F Target , while limiting total mortality leads to a decrease in F Target . Application of either approach can result in nonsensical results. Short-term gains in yield associated with high F Target values should be considered in light of potential losses in future yield if the high total mortality rate leads to a decrease in recruitment. Examples using yellowtail flounder (Limanda ferruginea) and Atlantic cod (Gadus morhua) are used to demonstrate that F Target can change when M increases within an assessment and to illustrate the consequences of different F Target values. When a change in M within an assessment is contemplated, first consider the amount and strength of empirical evidence to support the change. When the empirical evidence is not strong, we recommend using a constant M. If strong empirical evidence exists, we recommend estimating F Target for a range of stock-recruitment relationships and evaluating the trade-offs between risk of overfishing and forgone yield.Résumé : Traditionnellement, le taux de mortalité naturelle (M) dans une évaluation de stock est présumé être constant. Quand M augmente dans une évaluation, cela soulève la question à savoir comment changer le taux cible de mortalité par pêche (F Target ). Des considérations relatives aux recrues individuelles mènent à une augmentation de F Target , alors que le fait de limiter la mortalité totale mène à une réduction de F Target . L'application d'une ou l'autre de ces approches peut se traduire par des résultats qui n'ont aucun sens. Les augmentations à court terme du rendement associées à des valeurs de F Target élevées devraient être évaluées par rapport aux réductions potentielles du rendement futur si le taux de mortalité totale élevé se traduit par une baisse du recrutement. Des exemples basés sur la limande à queue jaune (Limanda ferruginea) et la morue franche (Gadus morhua) sont utilisés pour démontrer que F Target peut changer quand M augmente dans une évaluation et pour illustrer les conséquences de différentes valeurs de F Target . Quand la possibilité de changer M dans une évaluation est examinée, il faut d'abord prendre évaluer la quantité et la force des preuves empiriques qui appuient ce changement. Si ces preuves ne sont pas fortes, nous recommandons d'utiliser un M constant. Si les preuves empiriques sont fortes, nous recommandons d'estimer F Target pour une gamme de relations stock-recrutement et d'évaluer les compromis entre le risque de surpêche et le rendement non réalisé. [Traduit par la Rédaction]

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Section: Discussionmentioning

confidence: 99%

In what direction should the fishing mortality target change when natural mortality increases within an assessment?

Legault

Palmer

2016

Can. J. Fish. Aquat. Sci.

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“…Debate has been waged in the literature concerning the cause of the collapse of cod stocks and the role of fishing (e.g. Myers 1994, 1995;Myers et al 1996;Bundy 2001), seals (Bundy 2001;Fu et al 2001;Trzcinski et al 2007, Chassot et al 2009), and the environment (deYoung and Rose 1993). The evidence tends to suggest that seals were not the primary cause of groundfish declines, but have been identified as a potential impediment to cod recovery (Bundy 2001(Bundy , 2005aFu et al 2001;Swain and Chouinard 2008;Chassot et al 2009).…”

Section: Directly Examining Pairwise Species Interactionsmentioning

confidence: 99%

Ecosystem‐based fisheries management in the Northwest Atlantic

et al. 2011

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Introduction 153Living marine resource management context, history and background 154The fisheries 154The ecosystems 155Implementation of ecosystem-based approaches in living marine resource management 156Habitat closures and marine protected areas 157Models to provide tactical and strategic management advice 157Addressing questions on groundfish carrying capacity 159Directly examining pairwise species interactions 160 AbstractThe northwest Atlantic has had a notable history of living marine resource (LMR) exploitation. There have been calls for evaluating and improving approaches to manage those resources as stocks have undergone sequential depletion, with some dramatic instances of stock declines. The need for more holistic ecosystem-based approaches to manage LMRs has been increasingly recognized as part of these calls, along with the recognition that there are broader issues to consider when managing a fishery. We discuss some of the major efforts to this end which are extant among our institutions. We emphasize current initiatives to implement ecosystem-based fisheries management in the northwest Atlantic, with a focus on how advice based on the natural sciences supports an ecosystem-based approach. We present this information as a case study within a rich historical context of fisheries science and management.

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“…Trzcinski et al 2006, Chassot et al 2009 or the ecosystems in which they reside (e.g. Bundy & Fanning 2005, Savenkoff et al 2007) have been parameterised using the species and size composition of fish observed in the available seal diet samples.…”

Section: Discussionmentioning

confidence: 99%

“…, Savenkoff et al 2007). One such interaction, predation by pinnipeds, has received considerable attention (Mohn & Bowen 1996, Fu et al 2001, Chouinard et al 2005, Trzcinski et al 2006, Chassot et al 2009). The reason for this is likely twofold.…”

Section: Introductionmentioning

confidence: 99%

Evaluating the potential for grey seal predation to explain elevated natural mortality in three fish species in the southern Gulf of St. Lawrence

Benoît¹,

Swain²,

Bowen³

et al. 2011

Mar. Ecol. Prog. Ser.

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Despite 2 decades of very low fishing levels, numerous NW Atlantic demersal fish stocks have failed to recover from collapsed states or are presently collapsing. In the southern Gulf of St. Lawrence, adult natural mortality (M ) appears to be the demographic rate that most limits population productivity in at least 3 species: Atlantic cod Gadus morhua, white hake Urophycis tenuis and winter skate Leucoraja ocellata. The causes of elevated M are not well understood, though there is indirect evidence consistent with an effect of predation by grey seals Halichoerus grypus. However, direct evidence is lacking due to uncertainty in the seal diet. Consequently, Monte Carlo simulations were undertaken using data on the spatial overlap between the seals and the fishes and a seal food-consumption model, to estimate the plausibility that different seal-diet compositions could explain observed M levels. Under the simulation assumptions, we find that predation could explain up to 20 to 50% of M in adult white hake and cod even if these species comprise a small percentage of grey seal diets (< 25%). If seals consume some of these fish only partially, by selectively feeding on soft tissues, a predation effect becomes more plausible. Predation can also plausibly explain the observed elevated M in adult winter skate, even if they comprise a negligible (< 0.1%) percentage of the grey seal diet. Though the simulations deal with the factors that shape the potential for predation, a greater understanding of prey selection is required to conclude whether grey seals are actually adversely impacting these fish populations.

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Role of predation by harp seals Pagophilus groenlandicus in the collapse and non-recovery of northern Gulf of St. Lawrence cod Gadus morhua

Cited by 21 publications

References 54 publications

In what direction should the fishing mortality target change when natural mortality increases within an assessment?

In what direction should the fishing mortality target change when natural mortality increases within an assessment?

Ecosystem‐based fisheries management in the Northwest Atlantic

Evaluating the potential for grey seal predation to explain elevated natural mortality in three fish species in the southern Gulf of St. Lawrence

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