Estimating Improvement in Spawning Potential Ratios for South Atlantic Red Drum through Bag and Size Limit Regulations

Abstract

Based on a recent stock assessment of red drum Sciaenops ocellatus along the southern U.S. Atlantic coast (South Carolina to Florida), we calculated the possible gains in the static spawning potential ratio (SPR) from fishing mortality reductions (savings) produced by changing slot (size) and bag limits. Our method for calculating savings provides flexibility to address differences in commercial and recreational fishery regulations, regional stock conditions, and specific gear characteristics, and to account for discard mortality. Gear- and age-specific estimates of fishing mortality rates (F) for 1992–1997 resulted in savings from recreational fishery bag limits given a particular slot size. Relative changes in catch-at-age estimates modified the age-specific F estimates and, hence, the calculated SPR values. Additionally, recreational savings was adjusted to account for a release mortality of 10%. Static SPRs were estimated for (1) bag limits with increasing minimum size limits and a fixed maximum size and (2) bag limits with decreasing maximum size limits and a fixed minimum size. If the current slot limit (14–27 in total length) for the southern region remains unchanged, a bag limit of one fish per angler-trip would be required to attain the stated target of a 40% static SPR specified by the South Atlantic Fishery Management Council. However, the council's target could be attained with higher bag limits if the maximum size limit were reduced from the current level of 27 in, assuming no increase in effort on legal-size fish.