Growth, population age structure, and aspects of the reproductive biology of snowy grouper, Epinephelus niveatus, off North Carolina and South Carolina

Abstract

Sagittae (n=2,263) and gonads (n=870) from snowy grouper, Epinephelus niveatus, caught primarily with longlines, Kali poles, snapper reels, and chevron traps off North Carolina and South Carolina were examined 1) to compare growth rates, population
\nage structure, and sex ratio between two periods 1979–85 and 1993–94, and
\n2) to determine reproductive seasonality, size and age at maturity, and size and age at sex change. There were several indications that the population off North Carolina and South Carolina is overfished: 1) size at age of specimens caught with longlines and snapper reels has increased noticeably since the 1980s (possibly a a density-dependent population response to a high level of fishing mortality); 2) 81% of the fish caught with commercial longlines during 1993–94 were ages 1–6, the majority (56%) of
\nwhich were immature females; 3) the percentage of males in the population appears to have decreased significantly, from 7–23% in the 1970s and 1980s to 1% in the 1990s; and 4) mean length of fish landed in the longline fishery has steadily decreased from 65–80 cm in the early 1980s to 50–60 cm in the mid-1990s. There was a positive trend
\nbetween water depth and total length in fishery-independent samples. Histological
\nexamination of gonads revealed that mature gonads were present in 4% of the females at age 3, 52% at age 5, 95% at age 7, and 100% at ages >7 during 1993–94. The smallest mature female was 469 mm TL, and the largest immature female was 575 mm. Estimates of Length50 and Age50 were 541 mm (95% CI=529–553 mm) and 4.92 yr (95% CI=4.65–5.21 yr), respectively. Spawning females were caught during April through September on the upper continental slope off South Carolina at depths of 176–232 m. The size (767–1090 mm) and age (8–29 yr) of 97 male specimens and the capture of two specimens undergoing sex change provided conclusive evidence that snowy grouper are protogynous hermaphrodites.