Absolute Abundance and Survival of Juvenile Gags in Sea Grass Beds of the Northeastern Gulf of Mexico

The absolute number of individuals and survival of juvenile gags Mycteroperca microlepis in a 15.4-km2 shallow sea grass meadow in St. George Sound, Florida, were estimated by the Jolly–Seber mark–recapture method. Abundance was estimated within three sampling stations (150 m × 150 m) by means of standard (150 m, 1.8 km/h) tows with a 5-m otter trawl. The average densities (95% confidence limits), based on three stations sampled every 1–2 weeks from June to mid-September 1991, were 496 (251–744), 424 (210–670), and 549 (165–1,773) juveniles/ha. Trawl capture efficiencies and the effects of sea grass habitat conditions and size of juvenile gags were estimated so that absolute numbers could be determined outside the sampling stations. We estimated absolute abundance outside the sampling stations by trawling and dividing gag captures per standard tow by trawl capture efficiency estimates. The estimated absolute abundance of juvenile gags for the entire 15.4-km2 area was 943,615. Survival of juvenile gags in sea grass was near 100%, as estimated from trawl capture rates over the sampling period. Survival estimates were generally variable but were confounded by emigration from the sampling areas. The small-scale spatial pattern of juvenile gags was random. The results of this work provide the basis for establishing a juvenile recruitment index by providing quantitative estimates of juvenile abundance.