• A preliminary account of fisheries for the surf clam Spisula solida (L) (Mactracea) in Ireland

      Fahy, E.; Carroll, J.; O'Toole, M.; Hickey, J. (Marine Institute, 2003)
      Surf clams from seven stocklets on the west and south coasts are examined to provide a preliminary account of the fishery in Ireland. Spisula solida is the species harvested in every case. Most of the material was collected by commercial (box or hydraulic) dredge. A quantitative account of a surf clam bed is based on sampling by Day grab in Waterford Harbour. Ageing was by external shell sculpture. A limited comparison of this method with ageing by internal shell structure confirmed the method was usable and the results are presented on this basis with, however, reservations on the reliability of the approach. S. solida in Ireland had Linf of c 43 cm. Material gathered in Clifden, Co Galway, had an Linf of 35 mm. The Clifden stocklet was heavily fished when the material was gathered and a low value for Linf is attributed to the Lee phenomenon. A growth curve is constructed for only one stocklet, that in Waterford Harbour. Growth was slower than for S. solida in the North Sea, a possible consequence of heavy fishing also. The clam bed in Waterford Harbour was a low elevation bank of coarse (Spisula) sand. The area of the bed had become reduced during the preceding year by the invasion of silt grades displaced by earthworks upstream; these were injected into the coarse material to form a perimeter of the clam patch. Within the bed, the highest biomass of S. solida was 600 g/sq.m. Representation of age frequencies within samples suggests that heavy spatfalls of S. solida occur at irregular intervals and this complicates the calculation of F values from a catch curve. A yield per recruit curve is prepared for the clam patch in Waterford Harbour.
    • Some thick shelled whelk Buccinum undatum characteristics and fisheries in Ireland

      Fahy, E.; Grogan, S.; Byrne, J.; Carroll, J. (Marine Institute, 2006)
      Observations are presented on two whelk populations from the Cape grounds in Co. Donegal and the vicinity of Helvic Head Co. Waterford. Both co-exist with large populations of brown crab (Cancer pagurus) which is the likely explanation for their thick shells. In the south west Irish Sea (with which comparison is made) and in the Cape stocks, 83-88% of individuals were easily aged by reference to the operculum. Heavy calcification obscured structure in the case of Helvic animals and only 6% of these could be confidently aged. Helvic and south west Irish Sea whelk have similar L∞, but both Helvic and Cape whelk have more rapid early growth than in the Irish Sea. The density of whelk in the Helvic vicinity is insufficient to support a commercial fishery. The yield of whelk from other areas of the Celtic Sea is sporadic and slow to recover from exploitation. The Cape fishery shows signs of rapid depletion since most recent exploitation began there in 2003. The centrally situated sectors of the south west Irish Sea fishery are highly resilient and recover rapidly from heavy removals of biomass which can exceed 50% per annum. Maturation appears to take place at a lower size and age in the Irish Sea than in the other two whelk stocks and this is tentatively proposed as the explanation for their lower productivity.
    • A survey by hydraulic dredge of interstitial bivalves with commercial potential in Cill Chiaráin and Beirtreach buí Bays and along their connecting shoreline, Co Galway

      Fahy, E.; Carroll, J.; Browne, R.; Ní Rathaille, A.; Casburn, P.; Breathnach, S.; Norman, M.; Stokes, D. (Marine Institute, 2002)
      The shellfish co-operative, Comharchuman Sliogéisc Chonamara Teó (CSC) manages oyster and scallop in Beirtreach buí and Cill Chiaráin Bays, both of which are designated aquaculture areas. Cill Chiaráin is also a candidate Special Area of Conservation (cSAC). Various traditional fishing activities are carried on in the bays and CSC has rights to exploit clam species there. The work described here is a survey of interstitial clam species by hydraulic dredge between November 2001 and January 2002. Investigations were restricted from some of the upper bay areas where surface bivalve management was in progress. Much of the remaining areas within the Bays proved unsuitable for hydraulic dredging by virtue of the nature of the substratum. The exposed parts of the lower bays and the intervening coastline where the substratum was coarse sand (maërl or shell sand) were suitable for hydraulic dredging but bedrock and loose boulders often proved obstacles to towing. There was evidence of two assemblages of bivalves in the bays: one typified by Venus verrucosa, Venerupis senegalensis and Tapes rhomboides, all large and potentially valuable, occurred within maërl mixed with fine mud, the other whose most valuable components included Ensis arcuatus and Spisula solida, occurred in disintegrating maërl and in shell sand. The bivalve fauna in the two bays appeared to be typified by relatively high diversity and low biomass – which is accentuated by recent natural mortalities of Ensis arcuatus, a dominant species - and this is likely to prove a challenge to marketing; the Irish market typically exploits small numbers of clam species simultaneously. The terms of the licence under which CSC operates may provide opportunities to exploit clams within their designated area by means other than hydraulic dredging and these should be investigated. In view of the scientific values of the area and its status as a cSAC any plan to exploit its interstitial bivalves should be discussed with the relevant state agency.