• Bionomics of brown crab Cancer pagurus in the south east Ireland inshore fishery

      Fahy, E.; Hickey, J.; Perella, N.; Hervas, A.; Carroll, J.; Andray, C. (Marine Institute, 2004)
      The south east inshore brown crab fishery is delimited by the boundary of longitude - 6.3, within a coastal band of approximately 18 km (10 nm) in width and it extends along the south coast of Co Wexford for a distance of approximately 55 km; evidence for the stock extending into the inshore fishery west of the Waterford Harbour estuary is sparse. The fishery, whose maximum extent is calculated at 427 km2, yielded up to 700 t per year during the 1990s. In 2002 annual landings of 959 t accounted for 8.2 % of the national catch. The average overall LPUE was 0.87 kg per pot lifted in that year. Brown crab were landed whole or as claws, for human consumption, and clawed or, of poorer quality, with claws, to provide bait for the whelk fishery. This fishery is not considered to have any discard of legally sized crab and, in consequence, a large percentage of the landings is poorly conditioned. The stock is intensively fished; the amount of gear in use increased almost 5 fold since the mid 1970s. Landings per boat declined since the late 1980s although this may be as a result of sharing among a greater number of vessels. In 2002 an estimated 60 - 69 vessels fished brown crab in the peak autumn months. In 2002 and early 2003, 3,674 crabs were tagged in the inshore fishery; of these 14.4% were recaptured (12.8% of tagged females and 20.7% of tagged males). Observations made during tagging operations in 2002 only were used to clarify sex ratio and the incidence of recently moulted animals. The crab stock consists of a migratory female component which moves into shallow waters during the summer months probably to moult and mate. The male component is more sedentary. Both sexes move at speeds which slow during the summer months and increase again as the year advances; maximum speeds of 2 km/day were recorded for both sexes in the autumn. Movements by male crab were random while females adopted a south west trajectory. The greatest distance recorded for a tagged female crab was 136 km after 287 days at liberty. Other tagged females, reported by French vessels, were recaptured in ICES division VIIg which may be the over-wintering area for the stock. These animals had moved between 69 and 75 km from their release point. Tag reporting by the industry is considered to have been low. Based on the 'rate of tag recovery, the estimated rate of exploitation was lower than expected in an intensely fished stock. Population estimates were attempted using the Petersen formula and on the basis of assumptions about mortalities which recognized the phenomena of moulting and migration. The south east crab stock moves with the current which is westerly along the southern Irish coast. Recorded migrations were also short when compared with those of brown crab in the northern stock and in several other documented fisheries. The Nymphe Bank which adjoins the south east fishery has a water current pattern which retains larvae and it is known to have a high density of brown crab in the plankton. The existence of retaining currents may make the kind of long migrations which characterise others unnecessary for this stock. The status of the south east fishery is not known. LPUE indices provided by the Roscoff super-crabber fleet for ICES statistical division VIIg remained fairly stable between 1987 and 2002 but the quantity of crab captured by those vessels has declined considerably in most years since 1995.
    • The inshore pot fishery for brown crab (Cancer pagurus) landing into south east Ireland: estimate of yield and assessment of status

      Fahy, E.; Carroll, J.; Stokes, D. (Marine Institute, 2002)
      Although it is regarded as an important focus of brown crab Cancer pagurus landings, the fishery in south east Ireland is poorly documented and the official statistics are believed to under-record the species by a factor of 2-3. This appraisal of the south east Ireland brown crab fishery is based on >22,000 records of sales transactions from the 1990s and a comparison of the biological characteristics of landings in the late 1960s with thirty years later, in the context of increasing fishing effort. The three buyers who gave access to their books inwards for periods of the 1990s, purchase from the same fishing community and they compete for product but they occupy slightly different market niches: a vivier truck operator exports to Spain, a processor concentrates on autumn purchases of female crab for vacuum packing while the third buys crab claws for human consumption and crab bodies which are used as bait for whelk Buccinum undatum. Only the first sales of crab from 55 km of coastline are considered. In this area fishing effort doubled between 1972 and 1988 but expansion accelerated in the following decade by at least 128%; a single operator increased his effort by 80% between 1988 and 1998. In the 30 years after 1968, the number of pots per km of coastline rose by 241%.The sale of brown crab is recorded in consignments which are raised to live weights in the analysis. Consignment size fell steeply in the late 1980s and early 1990s after which it stabilised; adjusting the figures to allow for increasing effort accentuated the trend; at the same time consignment number rose. Allowing that a decline in consignment size was accompanied by an increase in pot number, consignment number should have risen by 310% to maintain landings at the level recorded in 1990; the largest recorded increase in consignment number was by 230% and while it is accepted that all sales transactions have not been obtained, it is likely that LPUE has been declining over the 1990s in real terms in this fishery. Increasing fishing effort during that time is seen as a product of better technology, stimulated by a desire to compensate for falling LPUE. Comparison of size and sex composition of the landings recorded in the late 1960s and the late 1990s are inconclusive. Depth of water and type of substratum are likely to influence the composition of inshore landings. An argument is presented that the south east inshore crab fishery is fully or over-exploited. It is likely to have an offshore component and such occasional data as are available on brown crab further south suggest that the offshore is an under-exploited fishery. In which case, the rate of interchange between the two components is likely to be crucial to the continued performance of the inshore fishery