Fri, October 28, 2016 11:00 AM - 12:00 PM AQUATIC ECOSYSTEMS RESEARCH LABORATORY (AERL). Speaker: Murdoch McAllister, Associate Professor, IOF; and Canada Research Chair in Fisheries Assessment
Abstract: In B.C., large lakes (>10,000 hectares) support recreational fisheries for trophy-sized rainbow trout. In the past few years, sharp declines in both the target and forage species have occurred on the largest of these fisheries. Since the 1960s the Kootenay Lake fishery for the Gerrard strain of rainbow trout (Oncorhynchus mykiss) had attracted thousands of anglers from across North America and contributed $5-10 million annually to the regional economy. Giant rainbow trout (up to 15 kg) increased to a 50-year historic high in 2012 and declined to historic lows in 2015 and 2016. The Gerrard rainbow’s only forage fish, kokanee (O. nerka), concurrently dropped from about 1-2 million to 0.02 million spawners. Fisheries biologists and managers remain uncertain about what triggered these declines and are considering options to try to rebuild both species and the fishery. In my talk I will review the development of a predator-prey-fishery dynamics model which was formulated as a model of intermediate complexity (MICE), i.e., a two-species Bayesian statistical catch-at-age model. The model was applied to describe the numerous fishery and ecological data compiled for Kootenay Lake and test hypotheses about the nature and strength of predator-prey interactions. A model that explicitly incorporated the predator-prey interaction explained long-term data of field and fishery surveys much better than single-species models without any interactions. Management reference points differed considerably between the model formulations. I will also review the application of the model to identify potential triggers of the recent declines in the fishery and the potential effectiveness of different management actions to rebuild the fishery.
Location: AERL 120