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There exist few recommendations for managing stocks with spasmodic recruitment, despite such stocks being not uncommon. Management procedures (MPs), developed for two species of redfish (Sebastes mentella and Sebastesfasciatus) in eastern Canada, are recommended for setting catch limits during periods of high and low abundance. A well-designed fishery-independent trawl survey is essential to provide advance warning of strong recruitment events and project future recruitment. Under an 'inventory management' strategy, a more appropriate aim in spasmodic stocks may be to maximize the number of years with 'good catches,' instead of maximizing total catches, as is traditionally considered in management strategy evaluation (MSE). Following a spasmodic recruitment event, an empirical harvest control rule based on larger fish delays the harvest of large cohorts by a few years, targets more commercially valuable fish sizes, and reduces the risk of growth overfishing. Capped MPs produced longer periods of large catches than uncapped MPs. MPs allowed for low harvests during periods of low abundance, thus avoiding unnecessary hardship in the industry. MPs evaluated here could be good candidates for other stocks with similar or less extreme recruitment variability. Il existe peu de recommandations pour la gestion des stocks a recrutement spasmodique, malgre le fait que ces stocks ne soient pas rares. Des procedures de gestion (PG) elaborees pour deux especes de sebastes (Sebastes mentella et Sebastesfasciatus) dans l'est du Canada sont recommandees pour l'etablissement des limites de prises en periodes de forte et de faible abondance. Une evaluation au chalut independante de la peche bien concue est necessaire pour pouvoir prevoir en temps opportun les episodes de fort recrutement et etablir des projections de recrutement futur. Dans une strategie de <>, un objectif plus pertinent pour les stocks spasmodiques pourrait consister a maximiser le nombre d'annees de <>, plutot que les prises totales, comme c'est traditionnellement les cas dans les evaluations des strategies de gestion (ESG). A la suite d'un episode de recrutement spasmodique, une regie de controle des prises empirique basee sur les plus gros poissons retarde la peche de grandes cohortes de quelques annees, cible les tailles de poisson de plus grande valeur commerciale et reduit le risque de surpeche du potentiel de croissance. Des PG plafonnees produisent de plus longues periodes de prises importantes que des PG non plafonnees. Les PG permettent des prises plus faibles en periodes de faible abondance, evitant ainsi des moments difficiles pour l'industrie. Les PG evaluees dans l'etude pourraient constituer de bonnes options pour d'autres stocks dont la variability du recrutement est semblable ou moins extreme. [Traduit par la Redaction], Introduction Developing an understanding of population dynamics and identifying management approaches consistent with this understanding have been among the chief aims of fisheries management science. To facilitate the achievement of [...]

Peer review of competing deepwater redfish (Sebastes mentella) assessment models revealed data inconsistencies where stock biomass decline shown by the survey in the 1990s was too rapid to be explained solely by reported catch. The models invoked different techniques to achieve fits, one by changing mortality at age and the other by survey weighting. The former fitted reported catch well, while the latter accepted a mismatch between reported and estimated catch. The assessments produced different estimates of historical stock size and future productivity. Interviews conducted with fishers of the stock suggested that catch was at least twice as high as the official record. In light of the fishers' evidence, the model that invoked a large change in mortality with age to follow reported catch closely now appears less credible. This serves as a warning against introducing new biological mechanisms without credible justification. This is an example of how indicators derived from fisher's knowledge, even if only from a small number of interviews, can be used to eliminate less plausible models. L'examen par des pairs de modeles devaluation du sebaste atlantique (Sebastes mentella) concurrents revele des incoherences dans les donnees qui font que labaisse de biomasse du stock relevee par la campagne devaluation des annees 1990 etait trop rapide pour que seules les prises declarees puissent l'expliquer. Les modeles font appel a differentes techniques pour le calage des donnees, un en changeant la mortalite selon l'age et l'autre en ponderant les evaluations. Le premier donne un bon calage des prises declarees alors que le second accepte un desaccord entre les prises declarees et estimees. Les evaluations produisent differentes estimations de la taille passee du stock et de sa productivite future. Des entrevues avec des pecheurs du stock portent a croire que les prises etaient au moins deux fois plus grandes que ce qu'indique le registre officiel. A la lumiere des renseignements provenant des pecheurs, le modele qui invoque un changement important de la mortalite selon l'age pour bien suivre les prises declarees apparait maintenant moins credible. Cela constitue une mise en garde contre l'introduction de nouveaux mecanismes biologiques sans justification credible. Il s'agit d'un exemple d'utilite possible d'indicateurs derives des connaissances des pecheurs, meme si elles ne decoulent que d'un petit nombre d'entrevues, pour eliminer les modeles moins plausibles. [Traduit par la Redaction], Introduction How to incorporate fisher knowledge (FK) into quantitative stock assessment is not always clear. FK information is often qualitative and may be perceived to be incompatible or even counterpoint [...]

We examined how the distribution of Atlantic cod (Gadus morhua) is influenced by abiotic (temperature, salinity, depth, suitable habitat) and biotic (stock biomass) factors based on tagging-recapture data collected from 1995 to 2008 by the Department of Fisheries and Oceans Canada in the northern Gulf of St. Lawrence. We calculated a centre of gravity index and a dispersion index using only individuals recaptured more than 1 year after tagging during the summer. The centre of gravity showed a northward expansion and eastward contraction in recent years, reflecting both fish distribution and changes in fishing effort. The dispersion index was significantly related to temperature, habitat suitability, and biomass but not to salinity or depth. These results indicate that interannual fluctuations of temperature and stock abundance both influence the dispersion pattern of cod. This new information could influence spatio-temporal fisheries management strategies for northern Gulf cod. Nous examinons comment la repartition de la morue franche (Gadus morhua) est influencee par les facteurs abiotiques (temperature, salinite, profondeur, habitat convenable) et biotiques (biomasse du stock) d'apres les donnees de marquage-recapture accumulees de 1995 a 2008 par Peches et Oceans Canada dans le nord du golfe du Saint-Laurent. Nous calculons un indice du centre de gravite et un indice de dispersion en utilisant seulement les individus recaptures plus d'un an apres le marquage pendant l' ete. L' indice du centre de gravite montre une expansion vers le nord et une contraction vers l'est au cours des dernieres annees, ce qui reflete a la fois la repartition des poissons et les changements dans l'effort de peche. L'indice de dispersion est relie significativement a la temperature, a la presence d'habitats convenables et a la biomasse, mais non a la salinite, ni a la profondeur. Ces resultats indiquent que les fluctuations entre les annees de la temperature et de l' abondance du stock influencent toutes deux les patrons de dispersion de la morue. Cette nouvelle information pourrait affecter les strategies spatio-temporelles de la gestion des peches des morues du nord du Golfe. [Traduit par la Redaction], Introduction Atlantic cod (Gadus morhua) is widely distributed in the North Atlantic and supports important commercial fisheries throughout its range. Because of the broad distribution and historical importance of the [...]

Abstract: Quantitative ecosystem indicators are needed to fulfill the mandate for ecosystem-based fisheries management. A variety of community metrics could potentially be used, but before reference levels for such indices [...]

Abstract: The use of fish community indicators based on size spectra has become popular in the development of an ecosystem approach to fisheries. Size spectrum theory arose from basic ecological [...]

Abstract: Excessive and unsustainable fishing mortality was the predominant factor in the depletion of Northwest Atlantic cod (Gadus morhua) stocks. However, despite imposition of severe catch restrictions for over a [...]

A Management Strategy Evaluation for the Atlantic redfish fishery in Fisheries and Oceans Canada management Units 1 and 2 in the Gulf of St. Lawrence and the Laurentian Channel was carried out. Three conservation objectives and four fishery objectives were formulated based on discussions in meetings between managers, scientists, industry members and other stakeholders. 18 performance metrics were defined to quantify how well candidate management procedures met each of the eight management objectives. A set of 18 operating models were formulated to evaluate the robustness of candidate management procedures to key uncertainties affecting the evaluation of management options. The operating models were age structured and fitted separately to data for the two redfish species, i.e., Sebastes mentella and S. fasciatus. A Bayesian approach to model fitting was adopted in which informative priors were applied for the steepness stock-recruit parameter for the Beverton-Holt stock recruit function, and historical deviates for cohorts that early research had concluded were strong ones. The models were fitted to time series of bottom trawl survey indices of abundance and length composition from Units 1 and 2, and length composition records of retained redfish catches in Units 1 and 2. Some of the key axes of uncertainty considered in formulating the operating models included uncertainty over fishery vulnerability-at-age, life history parameters, e.g., the rate of natural mortality and growth, the future time series of cohort strength, the magnitude and species composition of historical catches, and plausible values for the steepness stock-recruit function parameter. A set of six core operating models were judged to have higher credibility than the set of 12 stress test operating models which were still credible but according to technical and other considerations judged to be less so. Candidate management procedures were required to pass threshold values for performance metrics for the conservation objectives and were ranked according to the fishery performance metrics for the six core operating models. The management procedures (MPs) were model-free and included three key components. The primary one was a harvest control rule (HCR) which specified a catch limit based on the threeyear trailing average of Unit 1 trawl indices. The second specified the start-year for the HCR which varied between 2018 and 2022. The third specified whether a maximum cap to catch limits was to be applied and what the cap should be in each future year. If the MP was capped, a ramp cap was initially applied from the initial year to some intermediate year in the 40-year horizon. Here, the cap was increased in successive years, with the anticipated (1) recruitment to the fishery of the large 2011-2013 cohorts and (2) increases in industrial capacity. A maximum cap was then applied at the end of the ramp. For the conservation objectives, capped MPs outperformed uncapped MPs under most of the core and stress test operating models. Average catches retained and interannual variability in catches were much higher for uncapped than for the capped MPs. Four of the uncapped MPs failed on one of the stock conservation objectives for one of the core operating models. Under the less optimistic core and stress test operating models, for example, historical discarding is lower than that in the base case, there were a number of MPs that passed all stock conservation objectives and provided average future catches of about 24 kt over the next 10-20 years. Projected median total allowable catches (TACs) over the next five years from most MPs were sufficiently low as to constitute low conservation risk to the stocks. Stock conservation objectives that aim to reach in 10 years and then maintain the SSB of both species in the Healthy Zone were met with high probability in all tested MPs. The abundant small fish (<22cm) associated with the 2011-2013 cohorts results in predicted catches from all candidate MPs failing to meet the requirements of the Small Fish Protocol in 2018 and 2019. Small fish are expected to remain abundant in the catch until 2020. Exploratory analysis indicates that the performance of MPs with respect to three conservation objectives was improved and total catches were increased in simulations that assumed that the two species of redfish were perfectly distinguished in fishery catches, enabling species specific TACs. [ABSTRACT FROM AUTHOR]

Bottom trawling causes physical disturbance to sediments particularly in shelf areas. The disturbance due to trawling is most significant in deeper areas with softer sediments where levels of natural disturbance due to wave and tidal action are low. In heavily fished areas, trawls may impact the same area of seabed more than four times per year. A single pass of a beam trawl, the heaviest gear routinely used in shelf sea fisheries, can kill 5–65% of the resident fauna and mix the top few cm of sediment. We expect that sediment community function, carbon mineralisation and biogeochemical fluxes will be strongly affected by trawling activity because the physical effects of trawling are equivalent to those of an extreme bioturbator, and yet, unlike bioturbating macrofauna, trawling does not directly contribute to community metabolism. We used an existing box-model of a generalised soft sediment system to examine the effects of trawling disturbance on carbon mineralisation and chemical concentrations. We contrasted the effects of a natural scenario, where bioturbation is a function of macrobenthos biomass, with an anthropogenic impact scenario where physical disturbance results from trawling rather than the action of bioturbating macrofauna. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators but that high levels of trawling disturbance prevent the modelled system from reaching equilibrium due to large carbon fluxes between oxic and anoxic carbon compartments. The presence of macrobenthos in the natural disturbance scenario allowed sediment chemical storage and fluxes to reach equilibrium. This is because the macrobenthos are important carbon consumers in the system whose presence reduces the magnitude of available carbon fluxes. In soft sediment systems, where the level physical disturbance due to waves and tides is low, model results suggest that intensive trawling disturbance could cause large fluctuations in benthic chemical fluxes and storage.