Social-ecological dynamics and the persistence of the Lake Erie Ontario gillnet fishery

Abstract

Despite two centuries of commercial harvest and turnover in fish species composition in the Lake Erie food web, the Ontario commercial gillnet fishery persists, suggesting this system is ecologically stable. Simulations of harvest and fish population dynamics showed that more stable and persistent fisheries (i.e., low variability and high mean population size and harvests) were characterized by (1) adaptive harvest by humans within the range of real world productivity regimes, and (2) lack of competition among harvested species or when less productive species had a greater competition effect on more productive heterospecifics. Evidence for these mechanisms was sought among population data of the most harvested species, walleye (Sander vitreus), yellow perch (Perca flavescens), white perch (Morone americana) and white bass (Morone chrysops), estimated from Bayesian surplus-production models, as well as harvest, quota, and harvest interaction strengths. Harvesters exhibited aspects of adaptive harvest. Decreased walleye quotas led to greater proportional harvest of non-quota white bass. However, harvest did not change proportionally with biomass for 3 out of 4 species evaluated, inconsistent with mechanisms that promote stability. Inappropriate harvest response could be a result of misguided management advice during the 1990s, leading to overfishing (F>Fmsy) and fish species to be overfished (B<Bmsy). Competitive interactions among species were consistent with simulated food web structure that allowed for continued persistence of the fishery food web. This research reinforces insights from food web theory as a basis for fisheries management.