Incorporation of Discard Mortality in Walleye Stock Assessment for Saginaw Bay, Lake Huron

This study evaluated non-target walleye (Sander vitreus) catch and discard mortality in the Saginaw Bay, Lake Huron commercial trap net fishery. Prior to this research, discard mortality rates in the Saginaw Bay commercial trap net fishery, which primarily targets lake whitefish (Coregonus clupeaformis), and yellow perch (Perca flavescens) were unknown. In 2010, we quantified commercial trap net vessel catch and initial discard mortality. The high levels of walleye catch and mortality observed within Saginaw Bay had not been previously documented in the Laurentian Great Lakes. Walleye catch averaged over 120 individuals per trap net lift and 42% of those caught were morbid. Information on discard mortality was then incorporated into a statistical catch-at-age model for Lake Huron walleye allowing for the full framing of that mortality source relative to all other sources of extraction. A management strategy evaluation was further conducted using a stochastic simulation model to determine sustainable limits of fishing mortality in the present of ongoing bycatch mortality. A related value-of-information analysis determined that the cost of research to refine estimates of discard mortality would be outweighed by the benefits to the recreational fishery.