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The state-space model framework provides a natural, probabilistic approach to stock assessment by modeling the stochastic nature of population survival and recruitment separately from sampling uncertainty inherent in observations on the population. We propose a state-space assessment model that is expanded to simultaneously treat environmental covariates as stochastic processes and estimate their effects on recruitment. We apply the model to southern New England yellowtail flounder ( Limanda ferruginea) using data from the most recent benchmark assessment to evaluate evidence for effects of the mid-Atlantic cold pool and spawning stock biomass on recruitment. Based on Akaike's information criterion, both the cold pool and spawning stock biomass were important predictors of recruitment and led to annual variation in estimated biomass reference points and associated yield. We also demonstrate the effect of the stochasticity of the mid-Atlantic cold pool on short-term forecasts of the stock size, biomass reference point, and stock status. [ABSTRACT FROM AUTHOR]

The northeast US fishing industry and other stakeholders have considerable interest in the quality of bottom trawl survey results because of their importance in the setting of quotas, especially those directly derived from bottom trawl indices measured in catch per area swept by the survey net. Net spread (also referred to as wing spread) impacts catches and thus indices and, for the federal northeast bottom trawl survey, it is correlated with the depth at which a tow is performed. As part of an ongoing partnership between the Northeast Fisheries Science Center, the New England and Mid-Atlantic Fisheries Management Councils, members of the fishing industry, and academics in the region, an experiment to evaluate the impact of wing spread on the catchability of a number of species was conducted in the Fall of 2019 on the F/V Karen Elizabeth. The experiment targeted four species of flatfishes using a twin trawl rigging to collect simultaneous observations of catch and wing spread relative to a controlled optimal net spread. We analyzed these data to estimate the effect of net spread on relative catch efficiency and to evaluate the hypothesis that relative catch efficiency decreases as net spread departs from the optimal configuration. We found that, while the total catch was impacted by net wing spread (catches increased with increasing swept-area), there was no evidence of a wing spread effect on relative catch efficiency for any of the flatfish species. These results suggest that bottom trawl surveys should account for swept-area of individual tows, but that it is not necessary to incorporate species- or length-specific efficiency conversions based on the width of the net. • An extensive field study was conducted to assess the impact of trawl net wings spread on relative catch efficiency. • This experiment was designed in collaboration with industry members to address concerns about federal survey performance. • Results indicated wingspread impacted total weight of catches because a larger area was sampled. • However results suggested no significant impact of wing spread on the relative catch efficiency of the survey net. • Similar experiments conducted with industry may be helpful in exploring the impact of other conditions on survey performance. [ABSTRACT FROM AUTHOR]