Interspecific relationships and environmentally driven catchabilities estimated from fisheries data

A modelling framework is proposed to investigate possible interactions among fisheries, species, and shared environmental drivers. Two hypotheses that introduce temporal dependence among commercial and recreational catch and effort data from Lake Erie’s walleye (Sander vitreus) and yellow perch (Perca flavescens) stocks are evaluated using state space models. First, alternative forms of association between the mortality, recruitment, or migration of the two species are explored by modelling dependence in the interspecific process noise. Second, annual phosphorus inputs into Lake Erie, which are linked to the development of hypoxia, are tested for associations with the catchabilities of the fisheries. Interspecific process noise was positively associated, which suggests that mortality, recruitment, or migration is linked between walleye and yellow perch. Only for yellow perch, however, was annual phosphorus loading associated with catchability. The estimated probability that either stock fell below a common management benchmark was affected by the form of temporal dependence, which exemplifies the need to consider how interspecific interactions, shared environmental factors, and uncertainty in the process dynamics and observations affect stocks and their fisheries.