Catch Density: A New Approach to Shifting Baselines, Stock Assessment, and Ecosystem-Based Management

Abstract

Since 1995, researchers have worked to incorporate historical perspectives into fisheries management. however, problems of scale and distribution, data incompatibilities, and strictures of standard stock assessment models have limited success so far. here we offer a new metric, catch density (CD = catch/area fished), as a simple way to examine fish concentration that standardizes historical and modern catch by geographical area fished. we present three case studies based on historical gulf of maine fisheries. The first compares five discrete datapoints of annual catch and CD for american shad from 1634 to 1999. Changes in fish habitat, fishing effort, and geographical area make direct comparison of catch alone misleading, but CD declined three orders of magnitude over four centuries. The second study compares discontinuous and continuous time series of yearly catch and CD for 18 species and two species groups from 1887 to 1945 and from 1989 to 2005. modern catch is aggregated over each stock's entire range; the historical area is the gulf of maine. in each case, historical context explains the results. overall catch is higher today, while CD was higher historically, likely reflecting expanded vessel range and catch per unit effort. finally, when catch, CD, and average trophic level are compared for functional groups over the same time periods, CD accurately reflects shifts in trophic level not seen in catch alone. CD standardizes catch across spatial and temporal scales, timeframes, and geographic distribution. By integrating fisheries history with fisheries science, it offers a new perspective, quickly obtained, that may aid in developing ecosystem-based management.