The south eastern ray Raja spp. fishery, with observations on the growth of rays in Irish waters and their commercial grading.

Abstract

Five species contribute to the landings of the south eastern ray fishery, Raja microocellata being additional to the four more generally encountered in the Irish Sea. Fishing logs from 17 vessels were examined; they described more than 26,000 hours of fishing effort, most of it in division Vllg. Auction records contained a higher than expected proportion of small grades. The fishery is assessed as being more heavily exploited than the ray fisheries of division Vila. As far as possible, growth curves of rays in Irish waters were calculated on the fully recruited age groups. Values for L∞ were greater for females than males of all species; those for R. montagui and R. naevus are less than in other published accounts. Values of K range between 0.19 and 0.33 while values of to are between -3.009 and +0.49. In general, there is more variability in the values of to than is warranted by life cycles which are basically similar. Fishermen sort rays primarily on their size and secondarily on their external appearance, certain species having greater values than others. The supply of fish influences the outcome, insufficient quantities requiring that fish which would normally be segregated are bulked. Another Influence is the local occurrence of certain species. Statistical associations among species differ with grade, the smaller growing species rarely gaining access to the larger grades; when they do they are usually associated with species of lesser value. Rays are probably most effectively sampled by working on size grades within which samples are chosen at random.