The spurdog Squalus acanthias (L) fishery in south west Ireland

Abstract

Spurdog landings are made on all parts of the Irish coastline but most heavily concentrated on the west of the country. The fishery expanded to a maximum catch of just under 8,000 tonnes in 1985. The species had been pursued most intensively in the north west but effort is shifting southwards. This account of the south west Ireland fishery is based on material collected between April 1987 and March 1988, inclusive; information was collected by questionnaire and 5,300 individual fish were examined. Ageing was undertaken using the posterior spine: ages in the commercial catches ranged between 5 and 40+ years. The growth characteristics of the south-west Ireland spurdogs resemble those of the Scottish-Norwegian fish, but the Irish populations have a lower L∞. Female maturation takes place at a shorter length than in other populations hitherto investigated from British or Irish waters; the length at 50% maturity is slightly more than 74cm which corresponds with an age of 14 years. The fecundity of the south west Ireland spurdogs is relatively high. Mortality coefficients (Z) of fully recruited spurdogs are calculated from age 17 as 0.24 for females and 0.30 for males. Two life tables are constructed. The first, which is intended to ascertain the numbers of female whelps required to maintain numbers, suggests that the stocks are close to being overfished. The second life table examines the age structure of the breeding female component of the population but its outcome is inconclusive. In terms of its organization the south west of Ireland spurdog fishery can be considered as two separate fisheries: a trawl and a gill net fishery, the latter being regarded as the more detrimental to the prospect of sustained yield.