Diel, lunar, and seasonal spawning patterns of the Atlantic goliath grouper, Epinephelus itajara, off Florida, United States

Abstract

The diel, lunar, and seasonal timing of spawning in Atlantic goliath grouper Epinephelus itajara (Lichtenstein, 1822) in the United States is highly specific, occurring at night during new moon phases of August, September, and October. We derive these patterns from four lines of evidence apparent on spawning sites during the known spawning season: (1) from the transitory appearance of fish aggregations; (2) from simultaneous recordings of goliath grouper nighttime calls and nighttime vertical ascents that were far more frequent during the new moon phase than on the full moon; (3) from collections of goliath grouper eggs (genetically verified) at night downstream from known spawning sites; and (4) from significantly higher frequencies of both hydrated oocytes (indicating imminent spawning) and postovulatory follicles (indicating recent spawning) in ovarian biopsies taken from goliath grouper captured on spawning sites during new moon phases relative to full moon phases. We suggest that dark-night spawning is an adaptation minimizing egg predation by several species of scad [Decapterus punctatus (Cuvier,1829), Decapterus tabl Berry,1968, and Decapterus macarellus (Cuvier,1833)] and herring [Sardinella aurita Valenciennes,1847 and Etrumeus teres (DeKay,1842)] that are abundant on goliath grouper spawning sites.The seasonal spawning of goliath grouper, late summer–early fall, coincides with habitat conditions considered ideal for settlement of early juveniles in mangrove nurseries.