Age and Growth of the Knobbed Whelk Busycon carica (Gmelin 1791) in South Carolina Subtidal Waters

Abstract

Knobbed whelk, Busycon carica (Gmelin, 1791), age and growth were estimated using tagged and recaptured individuals (n = 396) from areas off South Carolina coastal islands. Recaptured whelks were at large an average of 298 d (4–2,640 d). Growth, an increase in shell length (SL), was evident in 24% of the recaptured whelks, whereas 29% of recaptured individuals were the same size as when released and 47% were smaller than the released size. Mean growth rate was <0.001 mm SL/d and 0.022 mm SL/d if decreases in SL were assumed to be zero. Smaller whelks (≤90 mm SL) at large for over one year grew seven times faster than larger whelks. The von Bertalanffy growth model: SLt = 159.5(1 − e−0.0765(t 0.4162)), was developed from the mark—recapture whelks exhibiting growth. Based on a South Carolina minimum legal size of 102 mm SL, whelks recruit into the fishery at 13 y of age. The longevity, large size at maturity and slow growth suggest the potential for over harvest of knobbed whelk. Future whelk management plans may wish to consider whether economically viable commercial harvest can be sustainable.