Growth, Mortality, Reproduction and Feeding of Knobbed Porgy, Calamus Nodosus, Along the Southeastern United States Coast

We studied age, growth, mortality, age/size composition, reproduction and feeding of knobbed porgy caught off North Carolina and South Carolina from 1972 to 1978. Maximum age determined from scales was 17 years for a 460 mm TL specimen. Annual increments in back-calculated length were 194 mm the first year, 57 mm the second year, and 42, 34 and 25 mm for years 3–5. Annual growth for ages 6–10 and 11–16 years averaged 13 and 12 mm. The von Bertalanffy growth model fitted to these data was L = 512 mm (1 – e ^{–0.174(1+0.878)}). Observed lengths at age for hook and line were significantly larger (P < 0.05) than trawl caught specimens by about 40 mm on average. Knobbed porgy were fully recruited to the recreational fishery at age 10 years (13.5% of the catch). Partial recruitment was gradual; ages 4–7 and 8 and 9 years made up 33 and 34% of the catch. Following full recruitment, ages 11–17 years accounted for only 15% of the catch. In contrast, knobbed porgy were fully vulnerable to the trawl at 7 years. Instantaneous mortality rates (Z) ranged from 0.526–0.742. Sex ratio at size and age data indicated that knobbed porgy are protogynous hermaphrodites, changing sex when they are 300–500 mm TL. Females were significantly predominant in the sample population (59%). Monthly mean gonosomatic indices suggest that fish spawn in May and June. Limited diet data showed that knobbed porgy are benthic carnivores preying primarily on mollusks, crabs, polychaetes and sea urchins, which they crush with their strong jaw and pharyngeal teeth.