Can the status of pelagic shark populations be determined using simple fishery indicators? Biological Conservation

Calls to develop alternative methods of assessing the population status of pelagic shark populations have increased substantially in recent years. An interim solution has been the development of more subjective evaluation of data series (indicator-based analysis) rather than predictions from complex stock assessment models. This paper examines the reliability of indicators for predicting population status (i.e. whether it has been overfished) and the fishing pressure (i.e. whether overfishing is occurring) of large pelagic sharks, based on these fishery indicator trends alone. We simulate a variety of large pelagic shark populations under different exploitation scenarios using life history parameters, and measurable fishery indicators information (catch-per-unit of effort - CPUE; and average length - AL). Our simulation results, designed to be generalized (via sampling of realistic distributions) but based loosely on the shortfin mako shark, showed that the reliability of fishery indicators for establishing population status is dependent upon the length of the time series analyzed. These caveats are critical to the proper evaluation of population trajectories that underlie the most important conservation decisions being made for sharks today.