Effects of fishing mortality on the age structure of marine fishes

Marine fisheries have a long history of exploitation, with the potential to shape many life history traits, particularly those that are heritable, such as age and size at maturity. Here, we analyze 43 marine fish stocks, using prewhitened cross-correlations, to examine the relationship between past levels of fishing mortality (F) and resulting shifts in age structure. Significant cross-correlations between F and age structure were evident in 88% of stocks examined. For 37% of stocks, changes in age structure followed changes in F, whereas in 39% of cases age structure preceded changes in F. Sensitivity and response time varied widely, likely a result of management, past exploitation, and life history. The efficacy of our method was tested empirically by simulations, revealing that certain time-series properties (e.g., high variance and low strength correlation) have potential to obscure underlying associations. Methods that allow for the identification of sensitivity and response time to pressures such as fishing contribute to the development of stock-specific management measures that can protect, or rebuild, age structure.