Effects of Bycatch on Salmon Fisheries and Escapement

Undoubtedly, marine bycatch of salmon juveniles would reduce the number of returning salmon; however, little studied are its effects on salmon fisheries, escapement, and management: at what level will bycatch affect management of salmon fisheries?   In this study, I constructed a salmon Life-Cycle model, with parameters adjusted to simulate Canadian stock Chinook salmon of the Yukon River.   Using this model, I compared the number of return, harvest, and escapement, and probability of achieving harvest and escapement goals (i.e., management success) between without bycatch (control) and with various bycatch levels (AEQ 3%-12%).  As bycatch level increased, the average run size and harvests declined, and the provability of management failure increased from 15% (no bycatch) to 20-30% (with bycatch).  However, because of high natural variability of salmon returns, it is improbable to attribute specific run failure to specific bycatch.