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The stock–recruitment relationship is the basis of any stock prediction and thus fundamental for fishery management. Traditional parametric stock–recruitment models often poorly fit empirical data, nevertheless they are still the rule in fish stock assessment procedures. We here apply a multi-model approach to predict recruitment of 20 Atlantic cod (Gadus morhua) stocks as a function of adult biomass and environmental variables. We compare the traditional Ricker model with two non-parametric approaches: (i) the stochastic cusp model from catastrophe theory and (ii) multivariate simplex projections , based on attractor state-space reconstruction. We show that the performance of each model is contingent on the historical dynamics of individual stocks, and that stocks which experienced abrupt and state-dependent dynamics are best modelled using non-parametric approaches. These dynamics are pervasive in Western stocks highlighting a geographical distinction between cod stocks, which have implications for their recovery potential. Furthermore, the addition of environmental variables always improved the models' predictive power indicating that they should be considered in stock assessment and management routines. Using our multi-model approach, we demonstrate that we should be more flexible when modelling recruitment and tailor our approaches to the dynamical properties of each individual stock. [ABSTRACT FROM AUTHOR]

Native populations of lampreys are declining throughout the Great Lakes drainage basin due to habitat loss and degradation, anthropogenic stresses, and stream treatment with lampricides to control the exotic Petromyzon marinus (Sea Lamprey). We surveyed 19 streams across Pennsylvania to determine the presence/absence of six species that were historically found there. In 2011, we found four species—Lamptera aepyptera (Least Brook Lamprey), Lethenteron appendix (American Brook Lamprey), Ichthyomyzon greeleyi (Mountain Brook Lamprey), and Sea Lamprey—in 14 creeks statewide. In 2012, we found three species—Least Brook Lamprey, American Brook Lamprey, and Mountain Brook Lamprey— in 8 creeks in the Allegheny watershed. Lampreys appeared to be extirpated at some sites. Historically, Ichthyomyzon bdellium (Ohio Lamprey) and Ichthyomyzon fossor (Northern Brook Lamprey) were reported, but we did not observe these species during our study. Substrate analysis indicated ammocoetes preferred substrates with a particle diameter of <0.3 mm in shallow, warm water. In tributaries of Lake Erie, lampricide treatment to control Sea Lamprey may be a major reason for the population decline of native lamprey species. [ABSTRACT FROM AUTHOR]