Individual-based yield-per-recruit analysis, with an application to the Atlantic sea scallop, Placopecten magellanicus

There can be considerable variation in fishing mortality risk among individuals in a stock, especially for sedentary or sessile species. An individual-based per-recruit model is proposed that can systematically deal with variability in fishing mortality among recruits. These variations can alter the yield per recruit (YPR) and biomass per recruit (BPR) that would be predicted from conventional theory. Where the YPR curve is concave, standard theory will tend to overestimate YPR, whereas the opposite will be true where the YPR curve is convex. Additionally, variations in fishing mortality among individuals can create a mismatch between conventional metrics of mean fishing mortality and that required to properly apply standard per-recruit theory. The concept of "recruit-weighted" fishing mortality is introduced to deal with this problem. An application of the model to the Atlantic sea scallop, Placopecten magellanicus, is presented that demonstrates that standard per-recruit theory may often misrepresent true YPR and BPR.