• Age, Growth and Maturity of Irish lobsters

      Gibson, F A (Department of Agriculture and Fisheries (Fisheries Division), 1969)
      A completely satisfactory method of ageing lobstem has not been developed. Gibson (1967) attempted to age lobsters using the principles of the von Bertalanffy equation as suggested by Beverton and Holt (1957). In this case the only determinable parameters were L∞, K and the annual growth rate was calculated from the recapture of tagged lobsters which had been at liberty for a period of one year, during which time they had or had not moulted. The smooth curve produced from these data suggested that lobsters first come into the catch, in large numbers at the end of their fifth year and are fully recruited in the sixth year. In reaching this age, the rate at which lobsters grow does not appear to be consistent, and does not appear to be so throughout the life span.
    • Appraisal of the whelk Buccinum undatum fishery of the Southern Irish Sea with proposals for a management strategy

      Fahy, E; Yalloway, G; Gleeson, P (Department of the Marine, 1995)
      A small occasional fishery for whelk in the southern Irish Sea expanded in the early 1990s, particularly in 1993, to provide meat for the Far East. Between 1990 and 1993 the weight of whelk delivered by a fisherman to factory per day remained stable but the fishing effort increased by 44%. The quality of landings declined, increasing proportions of smaller whelk being retained. The most heavily fished populations apparently display a Lee effect. An age at length key was prepared from 3,081 individuals and is used to transform length to age frequencies within the area of interest. The weight compositions of graded samples, abstracted from processors' financial accounts, were converted to population numbers. The age of full recruitment is reckoned to be five years over the area of interest although it may fall to four in the most intensely fished whelk patches. A Thompson-Bell yield per recruit curve has Fmax at F=0.3. Only one fishery, at the northern fringes of the fishing area, has an F value (read from the catch curve) of less than this. F values of fisheries at the centre and south of the exploited area are all situated on the negative slope of the yield per recruit curve. Male maturation occurs at a length of 70 - 80 mm in the least and 50 mm in the most exploited populations. Thus, a measure to protect broodstock would require a size limit of approximately 70 - 80 mm which would, coincidentally, approximate the size for maximum sustainable yield. It would also have a catastrophic effect on the existing fisheries. A size limit of 50 mm is already in force.
    • Benthic ecology of Dublin Bay in relation to sludge dumping: Fauna

      Walker, A J M; Rees, E I S (Department of Fisheries and Forestry, 1980)
      The Dublin Bay area in 1971 received sewage from about three quarters of a million people most of which was discharged or dumped off Howth to the north-east of the bay. Much sludge appeared to settle up and down the tide from the dump site, though finer particles entered the bay to the south. Additionally, dredge spoil was dumped south-east of the Baily up to 1971, but not in 1972. In 1971 and 1972 the effects of these organic wastes on the benthos were investigated. The fauna in the main part of the bay resembled the Acrocnida/Clymene community of Glémarec. On the sand banks there were also species of the Ophelia facies of Glémarec's deep Venus community. In the dumping area and in the southeast of the bay downtide of the dump site, where depths are greater, the faunas resembled the Nucula/Sabellaria community of Caspers. As well as having pollution indicator species, this latter community generally had greater faunal densities and diversities than elsewhere in the bay (except low divcrsities at the dump sites in 1971). Apart from a possible effect of depth, this suggests that the dumping was having an enriching rather than a degrading effect, although the probable sediment change since 1874 may imply a change in community type. Microvores (comprising surface-deposit and suspension feeders) were a prominent isotrophic group in the sampling area, and at the sludge-dumping site in 1971 particle feeders were abundant. All feeding types were more numerous in the organic waste settlement areas, though proportionally they appeared to be receiving differential benefits from the sludge and dredge spoil.
    • Captive rearing of larvae of the Dublin Bay prawn Nephrops norvegicus (L)

      Hillis, J P (Department of Agriculture and Fisheries (Fisheries Division), 1975)
      Wild caught Nephrops larvae were maintained in aquaria for as long as possible, in 1969, 1970 and 1971 together with a few which were hatched in the laboratory in 1971. Experiments were conducted at temperature ranges of 16°0 to 22°C and 11°C to 13 °C; the latter range is close to the ambient temperature of larvae in the sea. Direct observations, were obtained of the duration of all stages from first larval to third post larval (six successive stages in all), though percentage survival rates were rather low in some groups.
    • The cockle Cerastoderma edule (L.) on the South Bull, Dublin Bay: population parameters and fishery potential

      West, A B; Partridge, J K; Lovitt, A (Department of Fisheries and Forestry, 1979)
      The history of the Dublin Bay cockle fishery is reviewed briefly with emphasis on the period 1893-1913. Prior to 1900 some 80 tonnes of cockles are said to have been landed annually. In the subsequent decade the fishery declined and in recent times has been defunct. The population of cockles on the South Bull, Dublin Bay, was investigated in 1971 and 1972. Cockles were distributed throughout the beach, but occurred in greater density in the mid-shore region. The mean density, however, was low (9-13 cockles per sq.m) and the maximum recorded was only 51 per sq.m; this is consistent with the relatively exposed nature of the beach. The population was dominated by 0+ and 1+ age groups, though cockles as old as 9+ were collected. The age structure was consistent with regular annual recruitment, and the mean mortality figure for cockles in their second, third, fourth and fifth years was Z=0.76. The mean lengths at the end of the first four winters were 6.5, 22, 28.5 and 32 mm. The value of L∞ was 40 mm, and K = 0.6. The relationships between shell lengths and the weights of the shell, dry meat, wet meat, and shell + wet meat are described. The potential of this cockle population for commercial exploitation is considered, although in view of the low population density the catch per unit effort would probably be too small to be commercially viable at present. Yield curves indicate that a minimum legal length of 24 mm would be appropriate for protection of the breeding stock while allowing the optimum yield to be obtained. The potential sustained yield of the beach was estimated at 4 tonnes/sq.km annually at a fishing mortality of F=0.10.
    • The Distribution and Abundance of Animals and Plants on the Rocky Shores of Bantry Bay

      Crapp, G B (Department of Agriculture and Fisheries (Fisheries Division), 1973)
      A survey of the rocky shores of Bantry Bay is described. This is intended to serve as a means by which future changes may be detected, as well as providing an account of a hitherto undescribed area of the Irish coast. The abundance of littoral animals and plants was assessed at regular vertical intervals on forty transects, and the distribution patterns of these species are described and discussed in relation to two major environmental variables, emersion and exposure to wave action. The method adopted may be suitable as a standard method for surveying rocky shores, and this is discussed in relation to the objectives of the survey.
    • Distribution and ecology of oysters, Ostrea edulis (L.) in Kilkieran and Bertraghboy Bays, Connemara, Co. Galway

      Barry, M D (Department of Agriculture and Fisheries (Fisheries Division), 1981)
      An account of Kilkieran and Bertraghboy Bay oysters is presented, including data on their distribution and ecology in these bays. Growth and population structure are compared with other oyster-producing areas in Ireland. These data are reviewed in relation to the feasibility of redeveloping such areas of former extensive oyster production.
    • The Distribution of Mytilus edulis and Anomid Larvae in Kilkieran Bay, Co. Galway

      Wilson, J H (Department of the Marine, 1987)
      The temporal and spatial distribution of Mytiius edulis and Anomiidae larvae were recorded in Kilkieran Bay, Co. Galway, during 1984 and 1985. Only larvae close to settlement (M. edulis larvae > 250 µm length and Anomiid larvae > 160 µm length) were considered. M. edulis larvae were commonest in late July, mid-August and early September 1984 and in early May, mid-June and early September 1985, while Anomiid larvae were commonest in late June and rnid-July 1984 and mid-June and early September 1985. M. edulis larvae were generally found in higher densities at the mouth of the bay, while Anomiids were more evenly dispersed, with high concentrations over the oyster beds. There was no significant (P < 0.05) net import of either species of larvae into the bay over tidal cycles.
    • Distribution of oyster Ostrea edulis, mussel Mytilus edulis and Anomiid larvae in Bertraghboy Bay, Co. Galway

      Wilson, J H (Department of the Marine, 1988)
      Concentrations and shell lengths of Mytilus edulis, Ostrea edulis and Anomiid larvae were recorded from April to October 1985 in Bertaghboy Bay, Co. Galway. The gamete volume fraction off eggs in female mussels was recorded in an introduced cultivated population of mussels in the inner bay during 1985. Oyster larvae were commonest in July and September, but were concentrated in the upper bay. Mussel and Anomiid distributions were more variable. While the commercial stocks of mussels in the bay contribute to the larval pool, this input is small in relation to that from other sources.
    • A diving study on Dublin Bay prawns Nephrops norvegicus (L) and their burrows off the east coast of Ireland

      Hillis, J P (Department of Agriculture and Fisheries (Fisheries Division), 1974)
      During 1971 a team of divers studied the structure and numbers of entrances of burrows of Nephrops norvegicus in the Irish Sea off Clogherhead and counted their numbers in plots of 28sq.m area. Numbers of entrances found ranged from one to six with a peak at 3 and the densities of Nephrops norvegicus found ranged from 1 per 2.5sq.m downwards.
    • The escallop, Pecten maximus (L.), in Killary Harbour

      Minchin, D; Mathers, N F (Department of Fisheries and Forestry, 1982)
      Escallops (843) collected by SCUBA diving ranged from one year to an estimated seventeen years old and varied in shell height from 17mm to 164mm. They were predominantly found on the slopes on either side of the Harbour at depths between 6m and 35m; very few specimens were observed on the soft mud in the centre of the Harbour. The density of escallops increased towards the mouth of the Harbour. The greatest numbers of specimens of less than 50mm were observed at the mouth of Killary. Variability in age frequency distributions along either side of the harbour could be explained by differences in settlement intensity from year to year. Settlement appeared to be more successful on the southern side than on the northern side. It also appeared that local dispersion from settlement areas occurred rather than active migration. Escallops four years old or less swam regularly while swimming was less frequently seen in individuals exceeding five years of age. It was concluded that Killary Harbour was unsuitable for the collection of spat but may be a suitable area for escallop cultivation.
    • The exploitation of angler fish Lophius Spp. in Irish waters

      Fahy, E; Gleeson, P (Department of the Marine, 1992)
      Two species of European angler, Lophius plscatorius and L. budegassa occur In Irish waters. L piscatorius is dominant, particularly closer to the coast; L. budegassa becomes more important moving south and in landings from medium/deep water. Three stocks of anglers are recognized; this work concerns the fish in the central one, specifically in ICES Divisions Vllb, c and j,k. Anglers are taken in a mixed demersal fishery, and they are particularly associated with hake and megrim. Most landings of the species come from ICES Divisions VlIg-k. The species have traditionally been taken in a mixed demersal fishery, mainly by France and Scotland. Ireland's landings have increased from 100t in 1977 to in excess of 2,000t in recent years. Species composition of the landings was determined by port sampling. The proportion of Lophius piscatorius, while still dominant, has declined since the mid 1980s. A short CPUE time series from joint venture vessels fishing medium/deep water (approximately 200 m) shows no consistent trends although the values for 1991 were the lowest in the six years. Irish vessels take anglers of slightly greater weight than do their joint venture (Spanish) counterparts. Length frequency distributions of both species from the Irish trawl fishery are available from 1987 to 1991 inclusive. They are redistributed by age using French ALKs. The age distribution shows no particular trend for L. budegassa whereas that for L. piscatorius shows evidence of strong year classes from the mid 1980s passing through the population. The sharp reduction in angler CPUE in 1991 may have resulted from the exhaustion of strong mid 1980s year classes of L. piscatorius. A large plus group in the age distribution of L. piscatorius restricted interpretation of its population structure. Discarding of anglers appears to be very low in the south western Irish trawl fisheries, an estimate of 6.8% landed weight being used in this assessment. A catch curve for L. piscaforius suggested a value of Z+0.48; taking M=0.15 provides a value for F=0.33, to the right of Fmax and in general agreement with what has been concluded for this species in recent assessments.
    • The exploitation of Grey Mullet Chelon labrosus (Risso) in the south east of Ireland

      Fahy, E (Department of Fisheries and Forestry, 1979)
      Fisheries for grey mullet are widespread on the south coast of Ireland, the majority being small and irregularly operated. The largest, at Wexford in the south-east, is a summer fishery where recent catches are well documented. At Wexford nets of mesh perimeter 18.4 cm are fished as fixed engines by two methods known locally as stake and ring nets. The fish are captured by wedging in a single mesh. Data from the stake nets give an indication of catch per unit effort and this has shown no significant variation from 1969 to 1977. From June to September 1977 fork length and girth measurements were made from 2,121 net-captured grey mullet; age and weight were determined for 528 of these. Gonads from 341 fish were weighed and 154 ovaries were sectioned. The majority of net-caught fish were between 31 and 45cm fork length and 8 to 12 years of age. As the season progressed the gonads of maturing males expanded up to 700% by weight. Growth of the ovary was variable and smaller in degree. Ovary weight in autumn correlated well with mean oocyte diameter. On the basis of previously reported growth data for grey mullet in British and Irish waters and on the length of fish retained by the nets a mean age of catch of 9.6 years is expected. This figure was approached only at the beginning of the season; thereafter the man age of capture was lower.
    • The exploitation of megrim Lepidorhombus whiffiagonis by the Irish demersal fleet

      Fahy, E; Fannon, E (Department of the Marine, 1991)
      Two species of megrim occur in Irish waters but Lepidorhombus whiffiagonis constitutes the bulk of the catch by the Irish demersal fleet. Megrim is exploited as a by-catch of gadoid fisheries and is particularly associated with fisheries for Nephrops, angler and ray. Over the past 25 years megrim landings from the ICES divisions adjoining Ireland have fluctuated between 6,000 and 21,000 tonnes but there has been a gradual upward trend of which Ireland has taken an increasing share, rising to 1,800 tonnes in 1980. Spain exerts most influence in this fishery, being the location of the main market for megrim as well as having the greatest catching power. The most significant developments in the exploitation of megrim over the past twenty years are identified as the establishment of the European Exclusive Fishery Zone in 1977 and the entry of Spain to the Community in 1986. The importance of division Vlla as a producer of megrim has declined and the main fisheries for the species are in divisions VlIg-k. This assessment of the species is based on material gathered in 1989 and 1990 when length frequency data from the landings were collected from the west and south coasts. Lengths of approximately 8,000 megrim from landings from all divisions were collected in 1989, 28,000 the following year, and 1,400 were aged in the two years. Samples of the landings are comparable with graded exports from the fleet. The most intensive work was undertaken on a Nephrops and mixed whitefish fishery in Vllj. Megrim discards (round) are estimated to weigh 13.2% of landings (gutted). Few megrim of less than 20 cm were captured and no 0 group megrim was encountered. A growth curve is calculated for females and for females and males combined. For males the to value is outside the range of that parameter recorded elsewhere. Males are however a small proportion of the total, their higher mortality and slower growth giving them a skewed frequency distribution and reducing their contribution to the landings. Catch curves provided values for Z of 0.45 and 0.49 for females and combined sexes. Yield per recruit curves indicate exploitation is close to F max for females and on the negative slope for the sexes combined.
    • The feeding relationships of a small demersal fish community in the western Irish Sea

      O'Brien, K; Fives, J M (Department of the Marine, 1994)
      The feeding relationships of seasonal and resident fishes captured on a sandy substratum in the lrish Sea, in June and in September, were investigated. Stomach content analysis of the 17 species examined indicated four main feeding tvpes in the June sample and three in the September sample. The majority of the species analysed in both June and September showed the same food preferences in both months. Most of the fish species showed some changes in diet with increasing length (ontogenetic shift) - some became more specialized and others favoured more varied diet. There was no evidence of competition between specialist feeders within size groups.
    • The feeding relationships of the shanny, Lipophyrys pholis (L.) and Montagu's blenny, Coryphoblennius galerita (L.) (Teleostei:Blenniidae)

      O'Farrell, M M; Fives, J M (Department of the Marine, 1990)
      Collections of 279 specimens of Montagu's blenny, Coryphoblennius galerita (L.), and 276 shanny, Lipophrys pholis (L.), were made over a ten month period on a 2km stretch of the western shore of Mweenish Island on the west coast of Ireland. Further collections of 99 L. pholis and 8 C. galerita were made in March and April at two mainland sites. Sampling was confined to rockpools in the upper midshore region. The result of this bias was that while all age groups of C. galerita were collected, most of the L. pholis taken were less than two years old. Both species are omnivorous and exhibit definite seasonal feeding patterns. In general, C. galerita mutilate prey species, whereas only juvenile L. pholis are found to do this. Both species exploit a wide range of intertidal organisms. The ecological differentiation necessary for co-existence is evident, polychaetes are important only in the diet of juvenile C. galerita and bivalves and gastropods are important to L. pholis. There are only two food categories of importance to adult C. galerita and this may reflect the ecological stress on C. galerita of the habitat and the presence of L. pholis.
    • Field Observations on Larvae of the Dublin Bay Prawn Nephrops norvegicus (L.) in the Western Irish Sea

      Hillis, J P (Department of Agriculture and Fisheries (Fisheries Division), 1974)
      The occurrence of Nephrops norvegicus larvae in the western Irish Sea determined by survey cruises during 1969, 1970 and 1971 showed distribution patterns of the Irish coastal population which appeared to be, to some extent, separated from others adjacent (e.g. S.W. Manx), Vertical distribution showed the greatest numbers at 10-15 fm depth by day, ascending by approximately 5 fm around dusk; numbers deeper than 20 fm were very small except late in the season when they increased greatly. Differences between the Irish Sea and Faeroe, north~eastem English and Adriatic waters in larval season and rate of development were also found.
    • Fisheries for Ray (Batoidei) in Western statistical area viia, investigated through the commercial catches.

      Fahy, E (Department of the Marine, 1989)
      The status of the Irish Sea ray fishery is investigated using commercial catches of rays landed into two ports, Howth and Arklow. Approximately 80 45kg boxes were examined monthly over a year when approximately 100 individuals of each of the four contributing species were aged and measured. The species are R. naevus, montagui, clavata and brachyura. These are inter-mixed and casually segregated into four grades on their length. Weighting factors are provided to raise the sampled numbers to total landings. The frequency distribution of grades at the two ports is established from an analysis of some 5,700 commercial transactions. At Arklow, the pattern is stable from one year to another and apparently seasonal. Arklow boats have a short range. The pattern of landings at Howth is more complex; these vessels have a longer range and probably exploit various ages of rays. Growth in all four species occurs most actively during the summer months, slowing down in the winter. Annulus formation is not readily associated with the conventional birth date of 1 January. Coefficients of total mortality (Z) are high for the four species (0.38-1.00), higher than those found in a recent study of rays in Carmarthen Bay. R. brachyura is the most valuable species. R. naevus is the most numerous, possibly because it has a competitive advantage due to its age at full recruitment being one year later than those of the other three species. The yield of rays increases moving offshore and in a southerly direction in the Irish Sea. Landings into Irish ports by Irish vessels have increased between 1903 and 1985 although, until recently, ray as a percentage of total demersal landings was declining, from the 1950s.
    • The growth of Mytilus edulis from Carlingford Lough

      Wilson, J H (Department of Fisheries, 1977)
      The growth of Mytilus edulis at five stations in Carlingford Lough and two in Belfast Lough was calculated from annually produced growth rings. These rings were shown to be annual from measurements of the seasonal growth of marked animals on the shore. Shell tissue ratios were found to vary from station to station. Variations in growth are discussed in relation to sea temperatures, breeding cycles, salinity, pollution and level on the shore.
    • Investigations in Bantry Bay following the Betelgeuse oil tanker disaster

      Grainger, R J R; Duggan, C; Minchin, D; O'Sullivan, D (Department of Fisheries and Forestry, 1984)
      About 30,000 tons of Arabian light crude oil plus some bunker oil was lost from the tanker Betelgeuse in Bantry Bay following an explosion and fire in January 1971. Most of the oil was burnt, and in the intense heat was polymerised into an asphalt-like material which coated the shoreline or sank, disrupting fishing activity. Oil leaked intermittently from the wreck for over a year during the salvage operation, and some of this was treated very effectively by spraying concentrated dispersant from an aircraft. Evidence of residual circulation suggested that the northern side of the inner Bay would have been most threatened by the dispersed oil. Several species of fish spawned in the Bay in the months following the disaster and larvae and post-larvae were not seriously affected. Fishing activity was disrupted but, apart from periwinkles Littorina littorea (L.), no commercial stocks were observed to suffer mortality as a result of the spillage. There was some very minor contamination of escallops Pecten maximus (L.) but this did not prevent escallop spatfalls in 1979 or 1980.