Abstract

The temporal, spatial and behavioral dynamics of a spawning aggregation of yellowfin grouper were examined using underwater visual surveys, histological analysis, and hydro-acoustic tracking. Yellowfin grouper aggregated to spawn on the Grammanik Bank, a shelf-edge coral reef, during two or three consecutive months from February through April each year from 2004 to 2009. Fish arrived at the site on the full moon, and departed 10 to12 days after the full moon (dafm). Highly skewed male dominated sex ratios (> 4:1, M:F) on the full moon dropped to near unity by 4 dafm each month, indicating that males arrived at the spawning site early. Males were on average significantly larger than females. Aggregations of up to 600 fish swam elevated over the reef showing distinct coloration and behaviors. Spawning was observed in March and April 2008 and 2009 from 6 through 10 dafm. During spawning, 7 to 12 putative males followed one female, “rushing” her upward to release gametes. Spawning began near sunset and continued into the night. Histological analysis of ovarian tissue indicated that some females were capable of spawning on two consecutive nights, although the majority spawned every two or three nights. Most hydro-acoustically tagged fish came to the aggregation site two months each year, however left the area for weeks between spawning events. This yellowfin grouper aggregation is the most well studied for the species, and could provide information regarding the effectiveness of seasonal closures, along with the protection of spawning sites, for enhancing regional stocks of Caribbean groupers

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