The Law of the Sea requires that fish stocks are maintained at levels that can produce the maximum sustainable yield (MSY). However, for most fish stocks, no estimates of MSY are currently available. Here, we present a new method for estimating MSY from catch data, resilience of the respective species, and simple assumptions about relative stock sizes at the first and final year of the catch data time series. We compare our results with 146 MSY estimates derived from full stock assessments and find excellent agreement. We present principles for fisheries management of data‐poor stocks, based only on information about catches and MSY.

Ecosim models have been fitted to time-series data for a wide variety of ecosystems for which there are long-term data that confirm the models' ability to reproduce past responses of many species to harvesting. We subject these model ecosystems to a variety of harvest policies, including options based on harvesting each species at its maximum sustainable yield (MSY) fishing rate. We show that widespread application of single-species MSY policies would in general cause severe deterioration in ecosystem structure, in particular the loss of top predator species. This supports the long-established practice in fisheries management of protecting at least some smaller “forage” species specifically for their value in supporting larger piscivores.

The distribution of fishes is influenced by a host of physico-chemical and biological variables, including temperature and oxygen, prey abundance, feeding or assimilation rates, and predation risk. We used hydroacoustics and midwater trawls to measure the vertical distribution of pelagic fishes during a series of research cruises on Lake Superior's western arm in 2001 and 2004. Our objective was to assess vertical structuring in the fish assemblage over varying light levels. We observed variability in vertical structuring of both ciscoes (Coregonus spp.) and their primary predator, the siscowet (Salvelinus namaycush siscowet). Our results indicate that deepwater predators and prey migrate extensively over a diel cycle. This migration pattern is most consistent with changes in the distribution of prey resources for siscowet and diel variability in predation risk controlled by changing light levels for ciscoes. The magnitude of vertical migration in ciscoes increased with higher abundance of siscowets, supporting predation risk as a driver of cisco distribution. This study describes the extent of vertical migration in each group of fish, provides a statistical description of the pattern, and discusses the implications for trophic interactions in the Lake Superior food web.Résumé : La répartition des poissons est affectée par une quantité de variables physico-chimiques et biologiques, dont la température et l'oxygène, l'abondance des proies, les taux d'alimentation et d'assimilation et le risque de prédation. Nous avons utilisé des méthodes hydroacoustiques et des chaluts de mi-profondeur pour mesurer la répartition verticale des poissons pélagiques durant une série de croisières de recherche dans le bras occidental du lac Supérieur en 2001 et en 2004. Notre objectif était de déterminer la structuration verticale du peuplement de poissons en fonction de la variation des intensités lumineuses. Nous avons observé de la variabilité dans la structuration verticale tant chez les ciscos (Coregonus spp.) que chez leur prédateur principal, le touladi siscowet (Salvelinus namaycush siscowet). Nos résultats indiquent que les prédateurs et les proies d'eau profonde font d'importantes migrations sur un cycle journalier. Ce patron de migration s'accorde le mieux avec les changements dans la répartition des ressources des proies chez le siscowet et avec la variabilité journalière du risque de prédation contrôlée par les changements de l'intensité lumineuse chez les ciscos. L'étendue de la migration verticale des corégones augmente en fonction de l'abondance des siscowets, ce qui vient appuyer le risque de prédation comme facteur explicatif de la répartition des ciscos. Notre étude décrit l'étendue de la migration verticale chez chaque groupe de poissons et fournit une description statistique du patron de migration; les conséquences sur les interactions trophiques dans le réseau alimentaire du lac Supérieur font l'objet d'une discussion.[Traduit par la Rédaction] Hrabik et al. 22951991Eshenroder and Burnham-Curtis 1999;Knudsen and...

Several hypotheses have been proposed to explain diel vertical migration (DVM); however, they have generally been applied to DVM behavior of a single trophic level. We evaluate the costs (predation risk) and benefits (foraging rate and growth rate potential) of different hypothetical and observed DVM trajectories for a three-level pelagic food chain in Lake Superior containing opossum shrimp (Mysis relicta), deepwater ciscoes (Coregonus spp.), and lake trout (Salvelinus namaycush). Lake trout appear to be maximizing foraging and growth rates by tracking vertically migrating ciscoes, while the DVM trajectories of ciscoes suggests a trade-off between predation risk and growth. For ciscoes, two alternative DVM trajectories both minimize the ratio of risk to growth: a shallow trajectory that follows low light levels down to 80 m during the day and a deep trajectory (below 150 m) that tracks highest Mysis densities. Observed cisco DVM trajectories appear to follow the shallow high risk – high growth trajectory in 2001, but switch to the deep, low risk – low growth trajectory in 2004 when lake trout density was higher and the density of ciscoes was lower.

Fisheries management based on catch shares – divisions of annual fleet‐wide quotas among individuals or groups – has been strongly supported for their economic benefits, but biological consequences have not been rigorously quantified. We used a global meta‐analysis of 345 stocks to assess whether fisheries under catch shares were more likely to track management targets set for sustainable harvest than fisheries managed only by fleet‐wide quota caps or effort controls. We examined three ratios: catch‐to‐quota, current exploitation rate to target exploitation rate and current biomass to target biomass. For each, we calculated the mean response, variation around the target and the frequency of undesirable outcomes with respect to these targets. Regional effects were stronger than any other explanatory variable we examined. After accounting for region, we found the effects of catch shares primarily on catch‐to‐quota ratios: these ratios were less variable over time than in other fisheries. Over‐exploitation occurred in only 9% of stocks under catch shares compared to 13% of stocks under fleet‐wide quota caps. Additionally, over‐exploitation occurred in 41% of stocks under effort controls, suggesting a substantial benefit of quota caps alone. In contrast, there was no evidence for a response in the biomass of exploited populations because of either fleet‐wide quota caps or individual catch shares. Thus, for many fisheries, management controls improve under catch shares in terms of reduced variation in catch around quota targets, but ecological benefits in terms of increased biomass may not be realized by catch shares alone.