Temporal and Age-Related Variability in the Spawning of Two Co-Occurring Reef Fish Species, Blueline Tilefish and Snowy Grouper

The correlation between spawning bio­mass and reproductive potential in fish populations is likely weakest in the tropics and subtropics, thus computing annual reproductive output requires estimates of batch fecundity and annual number of batches.  The annual number of batches is often assumed to be invariant across age in stock assessment models, an assumption lacking empirical support in the literature.  Blueline Tilefish (Caulolatilus microps) and Snowy Grouper (Hyporthodus niveatus) are reef fish species that co-occur in rocky habitat on the Upper Slope off the southeastern U.S.  Both species are batch spawners, but Blueline Tilefish exhibits greater reproductive potential due to higher spawning frequency and longer spawning season duration.   The proportion of spawners with histological indicators of imminent or recent spawning among adult females (active+inactive) ranged from 0.71 to 0.93 during March through October in Blueline Tilefish, whereas the proportion in Snowy Grouper was < 0.50 during May through August.  Age had an effect on spawning proportion, as the proportion in Blueline Tilefish was 0.34 for Ages 2-5 yr, 0.73 for Ages 6-10, and 0.89 to 0.96 for Ages 11+.  In Snowy Grouper, the proportion of spawners between Ages 5 and 35 was fairly consistent but much lower (0.26 to 0.41).