The Need to Incorporate Size- and Age-Related Variation in the Spawning of Vermilion Snapper and Gray Triggerfish into Stock Assessments

The Marine Monitoring Assessment and Prediction (MARMAP) Program  in Charleston, SC, has investigated and monitored the abundance and life history of reef fish species off the US Southeast coast for 40+ years.  MARMAP data has supported regional stock assessments, which until recently used spawning stock biomass as proxy for reproductive potential, a weak assumption in batch spawners with indeterminate fecundity.   Initially, assessments that included fecundity data assumed the annual number of batches to be invariant across age, another weak assumption.  Vermilion Snapper (Rhomboplites aurorubens) and Gray Triggerfish (Balistes capriscus) occur on natural reefs on the mid to outer continental shelf.  Both species are batch spawners that exhibited variation in relative fecundity (per g body wt) with increasing fish size.  Interestingly, the relationship between age and the number of batches per spawning season was constant (~50) in Vermilion Snapper Age 2 and older, whereas in Gray Triggerfish, number of batches steadily increased from two at Age 2 to nine at Ages 6+.  A comparison of total egg production and spawning female biomass for Vermilion Snapper revealed that reproductive potential was noticeably underestimated by the biomass proxy at Ages 2-4.