• 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.
    • Reproductive biology and parasite (Perkinsus marinus) prevalence in the eastern oyster, Crassostrea virginica, within a Georgia tidal river

      O'Beirn, F.X.; Walker, R.L.; Jansen, M.L. (Elisha Mitchell Scientific Society, 1997)
      Recruitment, in 1992, of the eastern oyster, Crassostrea virginica, at one site (Flume Dock) within the Sapelo Island National Estuarine Research Reserve (SINERR) was lower than other sampling sites. Recruitment allied with gametogenesis and parasite (Perkinsus marinus) prevalence within the oysters was examined in 1993, in an attempt to explain the differences observed the previous year. Sampling occurred at three sites (Marsh Landing, Jack Hammock, and Flume Dock) along the Duplin River within the SINERR. Oyster recruitment in 1993 was reduced in all sites within the SINERR. No oyster recruitment was recorded at the Flume Dock site during any monthly collections or on collectors deployed for the duration of the sampling study. Oysters developed gametogenically and spawned at the Marsh Landing site two weeks prior to their occurrence at the Jack Hammock site. Gametogenic development in oysters at the Flume Dock site was retarded a further two weeks where the males appeared to spawn six weeks after the females, which could account for reduced recruitment levels at this site. Approximately, twice as many females as males occurred in all sites. Monthly sampling of prevalence and intensity of Perkinsus marinus (Dermo) revealed high levels of both parameters. Smaller oysters did display lower prevalences of Dermo than larger forms.