A simulation study of impacts of at-sea discarding and bycatch on the estimation of biological reference points F0.1 and Fmax

F0.1 and Fmax, estimated from age- or size-structured yield-per-recruit (YRP) analyses, are perhaps two of the most commonly used biological reference points in fisheries management. They are often used as management target (i.e., F0.1) and threshold/limit (Fmax) under the context of precautionary management. The estimation of F0.1 and Fmax can be influenced by parameters defining fish life history and fishing processes. Previous studies had evaluated many parameters that might influence the estimation of F0.1 and Fmax. However, few studies had been done to evaluate impacts of at-sea discarding and bycatch on the estimation of F0.1 and Fmax. Using data of the female Petrale sole (Eopsetta jordani) in the Oregon flatfish fishery as an example, we conducted a simulation study to evaluate how at-sea discarding and bycatch might influence the estimation of F0.1 and Fmax. The results showed that failure to incorporating discarding and bycatch, when they existed, had little impacts on the precision estimates for the two biological reference points, but might cause serious over-estimation of F0.1 and Fmax. This might consequently lead to overexploitation. The size-structured YPR analysis tended to be more sensitive to the variability in size-based processes such as discarding in the estimation of F0.1 and Fmax. This study demonstrates that failure to considering at-sea discarding and bycatch in the estimation of F0.1 and Fmax can have serious consequences to fisheries management and that such an impact on the estimation of F0.1 and Fmax may be different for age- and size-structured YPR models.