Size‐Dependent and Temporal Variability in Batch Number and Fecundity of Red Porgy, a Protogynous, Indeterminate Spawner, in the U.S. South Atlantic

Abstract

AbstractContemporary studies have shown that spawning stock biomass can be a poor estimator of total egg production, with the inclusion of fecundity tending to improve stock–recruit relationships. Since many U.S. fisheries now use spawning potential ratio (SPR) to define overfishing, an understanding of fecundity variation is especially valuable. We studied a commercially important, protogynous sparid, the Red Porgy Pagrus pagrus, off the southeast U.S. coast from 2007 to 2010 to estimate annual fecundity ( fa) as a function of batch fecundity ( fb) and batch number (nb) and to investigate size‐based and temporal variation. In total, 1,355 Red Porgy (241–478 mm TL) were collected; subsets of individuals were selected for estimating maturity, nb, and fb. Throughout the spawning season, the proportion of females that were capable of spawning increased to 100% on several dates and was generally higher among smaller females than current maturity information would predict. The proportion of females that were actually spawning was also as high as 100% on several dates, suggesting periods of daily spawning. Batch fecundity was positively related to TL, and the relationship varied significantly between years and among months within years. Spawning fraction (and thus nb) was also size dependent, with relationships varying between years and dependent upon the reproductive indicator used in calculation (i.e., spawning capability, postovulatory follicle presence, or hydrated oocyte presence). Annual fecundity estimates incorporating size‐dependent nb differed from estimates assuming size‐independent nb and varied between years. Through its effect on fa, the size dependence of nb ultimately affected perceptions of how fishing mortality rate influenced the SPR. Our findings show the importance of accounting for size‐dependent variation in nb when calculating fa in indeterminate‐spawning species and illustrate the potential implications for stock–recruit relationships and stock exploitation status.Received July 19, 2012; accepted January 21, 2013