UW Aquatic & Fishery Sciences Quantitative Seminar
Kirstin K. Holsman
Defining multi-species control rules using a bioenergetics-based multi-species statistical catch-at-age model (MSMt) for Bering Sea walleye pollock, Pacific cod, and arrowtooth flounder
Increasingly, ecological studies have demonstrated the importance of variability, physical disturbances, and food web, habitat, and species diversity to ecosystem structure. The importance of such bio-complexity to the natural world has similarly translated into the design and implementation of stock-assessment models used for fisheries management; many single species stock-assessment models now incorporate environmental or trophic indicators to increase predictive strength around forecasts of recruitment, weight at age, and thus future harvest limits under various management and climate change scenarios. Additionally, there is increased interest including ecological indicators in multi-species and/or ecosystem process-based management approaches and a variety of tools have emerged to address such management needs, including multi-species age-structured statistical models (hereafter referred to as MSM). MSM combines traditional catch-at-age stock assessment models with multispecies virtual population analysis models (MSVPA) in a statistical framework and uses abundance and diet data to estimate fishing mortality, recruitment, stock size, and predation mortality. MSM typically models the latter as a series of functional responses ranging in complexity from linear models to non-linear interactions. Since MSM can capture critical threshold effects that characterize many ecological interactions, such an approach also provides a statistical framework to evaluate and manage both the direct and indirect effects of fisheries harvest on multiple species. However, previous iterations of the model used static predator rations to predict species interactions and were therefore unable to capture climatic driven changes in predation and fishing impacts. In this study, we modified an existing MSM for three species of fish from the Bering Sea (walleye pollock, Pacific cod, and arrowtooth flounder) to incorporate temperature dependent predator rations estimated using Wisconsin bioenergetics models (i.e., MSMt). Additionally, we also used projections of the model to derive biological reference points (BRPs) for various harvest control rule approaches. Preliminary comparisons with analogous single species models show that increases in estimated predation mortality rates impact estimates of annual recruitment and productivity and also affect estimates of optimal harvest rates, especially under variable future climate scenarios. These results and methods for estimating multi-species BRPs will be discussed.
This is joint work with Jim Ianelli, Kerim Aydin, Andre Punt, and Elizabeth Moffitt.