Annual Fecundity in the Indeterminate Spawner, Pagrus pagrus, Incorporating Size-Based Variation in Reproductive Indicators

Recent declines in the U.S. South Atlantic stock of the protogynous sparid red porgy (Pagrus pagrus) have led to increased interest in the reproductive biology of this commercially important stock.  Studies on various species have shown that stock-recruit relationships are weakened when spawning stock biomass is a poor estimator of egg production, catalyzing fecundity research.  We conducted regular sampling of P. pagrus off the coast of North Carolina throughout two main spawning seasons to estimate total annual fecundity as a function of batch fecundity and batch number, and describe temporal patterns of egg production.  In females, relationships between three binary reproductive indicators (spawning capability, post-ovulatory follicle presence, and hydrated oocyte presence) and body size were tested using logistic regression; the resulting relationships were used in size-specific calculations of batch number. We sampled n = 1,284 P. pagrus 241-478mm total length (TL), from port and at-sea samples, randomly selected n = 805 for histological maturity staging and estimation of batch number, and estimated batch fecundity for n=285 ripe females with the use of digital imaging.  During the known spawning season, the proportion of females capable of spawning increased to nearly 100% suggesting that all females ≥241mm TL were mature, suggesting a size at maturity smaller than other recent estimates.  Within the spawning season, the proportion of females spawning on a given day was as high as 100% and was generally dome-shaped but fluctuated substantially.  Batch fecundity was best predicted by TL, and this relationship varied significantly between years, and between months within years.  The presence of reproductive indicators varied with body size and these relationships varied between years; size-specific calculations of batch number strongly effected annual fecundity estimates.  This research represents the most comprehensive study of egg production in a wild stock of P. pagrus.  New calculations allowing batch number to vary with body size addresses an important issue in estimating annual fecundity in species with indeterminate fecundity.