IRELAND'S VELVET CRAB (NECORA PUBER (L.)) POT FISHERY

Abstract

Velvet crabs (Necora puber (L.)) are taken mainly as a by-catch in the pot fishery for large crustaceans. N. puber is negatively associated with spider crabs (Maja brachydactyla Balss) and positively associated with brown crabs (Cancer pagunus L.). In the Irish Sea, which yields small quantities of brown crabs, velvets have greater commercial significance, and they are targeted. Individuals from 28 samples of velvet crabs were described to characterise landings of the species. The female:male ratio was low, as was fecundity, which was typical of the northern European subgrouping of the species. Carapacewidth frequencies of males and females were disaggregated by a Bhattacharya plot into six groups of males and four groups of females. Females have been described as having a lower life expectancy than males in this species. An age of eight to ten years is proposed as the required age to achieve maximum size in the male. Average male and female size and weight within samples correlated highly significantly, and males were used as indicators of population structure as more information was obtained on males. Age at full recruitment of males correlated inversely with landings over a period of ten years; the mortality coefficient (Z) correlated positively with landed weights. There are no conservation measures currently in force in Ireland for this species, but it is difficult to hold in captivity, and most of the trade is live export. Hence this species is landed at 20-34% of potential landing places, only where suitable buyers are available, although the species is believed to occur in all coastal waters. Spatially discontinuous exploitation fabours a sustainable velvet fishery.