• 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.
    • Distribution, population structure, growth and reproduction of the razor clam Ensis arcuatus (Jeffreys) (Solenaceae) in coastal waters of western Ireland

      Fahy, E.; Norman, M.; Browne, R.; Roantree, V.; Pfeiffer, N.; Stokes, D.; Carroll, J.; Hannaffy, O. (Marine Institute, 2001)
      Samples of razor clams, Ensis arcuatus, the species which makes up the majority of landings from the west coast of Ireland, were collected by commercial fishery methods, in association with the dredge fishery and by scuba diving, from three locations off the coast of Co Galway. E. arcuatus occupies coarse sand (of maerl and shell fragments) and rarely co-exists with the other common species of the region, E. siliqua. E. arcuatus were aged, an age-length-key devised for them, and growth parameters (Linf, k and t0) were calculated. Their maturation state was established by histological examination. Evidence suggests that Ensis arcuatus is mainly a spring spawner, although some spawning appears to take place in most months, with a spatfall in June/July. Maturation commences in its third year. Asymptotic length is achieved at 10 years, approximately, and there was little variability in growth among the three sampling areas or between the sexes. In a small bed of razor clams in Cill Chiarain Bay, Co Galway, there would appear to have been a spatfall in most, if not all, of the past 15 years. The quantitative distribution of E. arcuatus in a single bay within the boundaries of Comharchuman Sliogeisc Chonamara Teo, Co Galway, was estimated by divers salting quadrats of 0.33 m2. The razor clam community is divided into a generally distributed fraction occurring at low density (described as the non-bed) and at a relatively higher density (described as the clam bed). The bed was situated in the lee of reefs, which is usually the case for this species along the Atlantic seaboard. More than 90% of the biomass was above the E.U. minimum size limit.
    • The Dundalk Cockle Cerastoderma edule Fishery in 2003-2004

      Fahy, E.; Carroll, J.; Murran, S. (Marine Institute, 2005)
      A cockle fishery in Dundalk Bay has been infrequently documented since 1970. Cockle bearing sands and muds are 44.5 km2 in extent. The bay, which is in an SPA and a cSAC also supports large numbers of overwintering birds, of particular relevance is the oystercatcher (Haematopus ostralegus). In 2003 and 2004 when an assessment of the fishery was undertaken, cockles ranged from 0 to 8+ years of age, but the vast majority were 0 and 1+ animals. Growth was rapid and 53% of asymptotic length (49.1 mm) was achieved at the first winter. In agreement with observations elsewhere, the density of the rapidly growing animals was very low. The estimated cockle biomass in spring 2004 was 1,654 tonnes comprising 143 million animals. A survey undertaken in spring 2004, suggested that spat falls contributing to the population may not have been evenly distributed throughout the Bay. Condition factor in 2003 and 2004 did not conform to an expected seasonal pattern, suggesting that some parts of the area supported better growth rates than others. Cockle landings from this fishery are of good quality. Cockle size is at the upper end of the range in Britain and Ireland and the majority of individuals landed by suction dredging were 1+ years old. Raked landings contained more 2+ cockles than suction-dredged ones. Damage to cockles discarded by suction dredging followed the pattern reported elsewhere and damage rates increased with the size of the animals. Some cockle landings have probably always been made in Dundalk Bay by picking and raking, but 2001 marked the beginning of an expansion of the dredge fishery, whose landings exceeded 200 tonnes in 2004. The necessity for controls and management of this fishery in the context of EU legislation and particularly within the constraints of the Habitats Directive is briefly examined.
    • Fishery Associated Changes in the Whelk Buccinum undatum Stock in the Southwest Irish Sea, 1995-2003

      Fahy, E.; Carroll, J.; Hother-Parkes, L.; O'Toole, M.; Barry, C. (Marine Institute, 2005)
      The whelk fishery of the southwest Irish Sea had a turnover of approximately €18 million and employed 250 people directly and indirectly in catching and processing in 2003. In the nine years, 1995-2003 inclusive, whelk landings to Ireland from the southwest Irish Sea fluctuated between 3,800 and almost 10,000 tonnes(t) per year; from an estimated 5,000 – 15,000 boat-days annually. A collapse in landings was recorded in 1997 and again in the spring of 2004. The fishery is divided for assessment purposes into four sectors, the central two consisting largely of nursery area and the north and south extremities of the fishery populated by more older, larger and mature whelk. Logbooks were not completed by fishermen participating in this fishery which was, in theory, managed by size limit, but the regulations were not enforced. Boats fishing whelk made daily fishing trips and daily weights recorded by processors were used to estimate biomass in each of the sectors by depletion regressions. Total biomass fluctuated between 12,720 t in 1999 and 37,319 t in 2002. The estimates based on a full season’s landings are used to compare the fishery from one year to the next and to supply weighting factors for other parameters of the population. Exploitation rates were lowest in one of the central sectors of the fishery (where they averaged 27% annually). At the southern extremity they averaged 39%. Depletion estimates based on landings records from approximately April to 15 June provided higher exploitation rates and lower biomass. The mortality coefficient Z, calculated from a catch curve, peaked in two years, 1998 and 2002, as did an index of recruitment. The age at full recruitment declined after 2000. Throughout nine years of documented history, one of the central sectors of the fishery assumed progressively greater dominance over the others, providing 77% of the landings from the entire fishery to its ports in 2003. Some sectoral changes to the whelk population may be irreversible: the oldest animals have been removed from the northern extremity of the fishery and while the whelks which are exploited at the southern end between 2000 and 2003 were similar in size to those exploited in the mid-1990s, their tonnage between 1999 and 2003 decreased from 47 to 4% of the landings in 1995. A substantial recruitment in 2001 or 2002 was followed by an increase in fishing effort of 42% between 2002 and 2003 and this is identified as the reason for the collapse in 2004.
    • 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