• Observations on the status of bass Dicentrarchus Labrax stocks in Ireland in the late 1990s

      Fahy, E.; Forrest, N.; Shaw, U.; Green, P. (Marine Institute, 2000)
      Investigative work was undertaken in 1996 to ascertain the strength of sea bass stocks following the introduction of a range of conservation measures which effectively extinguished the legitimate commercial fishery for the species. Information was sought from two sources: estimation of the age composition of the samples and the growth of bass by examining scales from exploited fish. An estimate of the density of juvenile pre-recruit bass was made from a seine net survey undertaken in various estuaries along the south coast. Scales sent in by anglers and obtained through the regional boards from illegally netted fish indicate that a high proportion of bass landed between 1996 and 1998 belonged to the 1989-year class, which had been reported to be exceptionally large in Britain. Back-calculations of length-at-age from the scales of these and seine-netted bass suggested that growth improved in the later 1980s in response to higher sea temperatures but has since declined. Work on an index of juvenile abundance began with 59 seine net hauls made in August 1996 and 1997. On these the areas most likely to support bass were characterised; O-group bass were encountered more frequently than any other age group. Sites most likely to support bass were mud flats overlaid with shallow and still water which had a salinity range of 17 to 22% and bass were associated with certain species of estuarine fish and crustaceans; bass were negatively associated with other species occupying the deeper and more sandy parts of estuaries. Sampling stations for O-group bass have been selected in Youghal Harbour and Wexford Harbour. Further exploratory work is required to extend the list of stations. It was concluded that there has been a temporary increase in the numbers of sea bass, as has been reported by fishermen in Ireland, as a result of more favourable temperatures in the late 1980s. Growing conditions appeared to have deteriorated in the later 1990s and the summer growth ofO-group bass was the weakest in 1999 over the 4 years investigated. A time series of O-group abundance is too brief to permit any conclusions to be reached. However, it can be stated that the recorded densities of juvenile bass between 1996 and 1999 were sparser than would be expected in south east Ireland in view of the supposed heavy winter concentrations of the species in the Celtic Sea.
    • Population dynamics, age, growth and maturity of lemon sole Microstomus kitt (Walbaum 1792) sampled between 2000-2002 off the west coast of Ireland.

      King, P. A.; Hannan, J. F.; McGrath, D.; Veldon, M. (Marine Institute, 2006)
      The age, growth, maturity and population dynamics of lemon sale (Microstomus kin), from commercial catches off the west coast of Ireland (ICES division Vllb), was determined for the period November 2000 to February 2002. The maximum age recorded was 14 years. Males of the population were dominated by 4 year olds, while females were dominated by 5 year olds. Females dominated the sex ratio in the overall sample, by month sampled, by age class and by size (from 22cm in total length onwards. when N > 20). Mature male and female lemon sale were encountered at age 2 and above. Von Bertalanffy growth parameters were estimated using the method of Rafail (1973). In recent years, the lemon sale has exhibited a smaller asymptotic length (L∞ = 34.47cm), faster growth rate (K = 0.1955) and younger age at first maturity than in the same area in 1978-1979. These changes are indicative of a decrease in population size following exploitation.
    • A review of potential techniques to reduce the environmental impact of demersal trawls

      Linnane, A.; Ball, B.; Munday, B.; Van Marlen, B.; Bergman, M.; Fonteyne, R. (Marine Institute, 2007)
      Concern over the possible effects of trawls on the seabed has existed almost as long as the fishing method itself, with early concerns being voiced by fishermen themselves as far back as the 14th century. With the advance in technological developments of trawling gears (i.e. weight and size), particularly over the latter part of this century, the increase in the number of fishing vessels, engine power etc., these concerns are increasingly gaining international public and political importance. This review is divided into two sections. Section 1 gives an overview of the physical and biological effects of bottom trawling and section 2 gives an overview of potential gear modifications.
    • A second assessment of the whelk fishery Buccinum undatum in the southwest Irish Sea with particular reference to its history of management by size limit

      Fahy, E.; Masterson, E.; Swords, D.; Forrest, N. (Marine Institute, 2000)
      Whelk landings in the southwest Irish Sea increased from 56 t in 1990 to 6,575 t in 1996 after which they stabilized between 3,600 and 4,600 t annually. At its peak the fishery supported approximately 80 vessels but this number has halved since. In 1994 a size limit of 50 mm was introduced for conservation purposes. Age based assessments of the landings were carried out in 1994, 1996, 1997 and 1999, for which purpose the fishery, ranging from 52º10’ to 53º30’, is divided into four sectors. Landings to the four sectors display biological characteristics which indicate the occurrence of a number of stocklets rather than a single stock unit. Whelk in the south west Irish Sea are relatively thin shelled and the fishery has a low density of large crustacean predators. There is no evidence of contamination by TBT. The northern and southern ends of the fishery have relatively lower densities of larger/older animals; the centre sectors have smaller whelk of shorter life span at higher densities, some of them showing symptoms of a Lee phenomenon and slower growth. A survey of cpue places heaviest densities on the Codling and Rusk Banks, in strong tidal currents, at depths of < 20 m. Growth and maturation rates vary among stocklets. L∞ ranges from 102 to 116 mm. Length at 50% male maturation is usually within the range of 63 – 68 mm and ages of 6.1-7.2 years although landings to one sector have a 50% male maturation rate of 83 mm and 8.5 years of age. The existing size limit of 50 mm would, at best, afford protection to 40% of spawning males. Compliance with the size limit has been poor. From 20 to 33% of total landings in any of the assessed years have been less than the legal limit and in 1994 51% of landings in one sector were below the acceptable size. Trends in cpue have been monitored since 1990 and some areas do not show any marked tendency. On the contrary, some fishermen in the centre sectors improved their yield between 1994 and 1998. There are two explanations for this: the movement of pots onto virgin ground and the fact that fewer fishermen are competing for landings in the same areas. Whelk have responded to a reduction in fishing effort since 1996 immediately following which mortality coefficients (Z) were highest (0.79); they declined to an average 0.61 in 1999. In terms of yield per recruit however they remain high. The southern sector of the fishery is regarded as being most depleted although very few subsize limit whelks were caught there. The survival of the whelk fishery in the southwest Irish Sea is attributed to the instability of the market which is dominated by a single customer, South Korea. A more effective size limit for this fishery would be 68mm (83 mm in the northern sector) and this is considered unrealistic, suggesting that alternative management measures will have to be considered.
    • Sediment characteristics and local hydrodynamics and their influence on the population of Nephrops around Ireland

      O'Sullivan, David; Lordan, Colm; Doyle, Jennifer; Berry, Alan; Lyons, Kieran (Marine Institute, 2014)
      The Norway lobster, Nephrops norvegicus, is the second most valuable commercial spe-cies landed from Irish waters. The species is dependent on muddy seabed sediment in which burrows are constructed. Larvae are hatched from the seabed into the water column. The distribution of Nephrops depends in part to the presence of suitable sediment and also from larval supply modulated by existing local hydrodynamic regimes. The pelagic stage of the life-cycle is governed by both physical and biological factors including temperature, water speed and larval maturation rate. This study encompasses three aims, 1: to synthesise available sediment data and examine the spatial extent of potential Nephrops habitat in waters around Ireland, 2: investigate local hydrodynamic conditions on Nephrops fishing grounds which are likely to be encountered by planktonic larvae following hatching and 3: to employ a particle tracking model to study the potential dispersal fields of Nephrops larvae from individual fishing grounds and assess stock connectivity. The study finds that larval distribution between fishing grounds is dependent on variable seasonal conditions, the geographical size of an area and its proximity to other grounds. Fishing grounds in the Irish Sea and Porcupine Bank are isolated from other areas, whereas grounds in the Celtic Sea exhibit a high degree of connectivity and should be considered as a meta-population. Successful annual recruitment to the adult population of this species is largely dependent on favourable environmental conditions which enable the re-seeding of the same or adjacent grounds.
    • The state of stocks of cod, whiting, sole and plaice on the west and southwest coasts of Ireland

      Wheatley, S. B.; Connolly, P. L.; Woods, F.; Keatinge, M.; Doherty, M. (Marine Institute, 1999)
      Stocks of cod, whiting, plaice and sole in ICES Divisions VIIb,c and VIIj,k are an important part of the Irish fishing resource yet, until 1993, were not subject to any assessment. Landings of these stocks in 1996 were valued at £8.6 million, representing 17% of the overall value of all Irish landings of demersal species. In 1993, the Fisheries Research Centre initiated a stock monitoring programme with the aim of providing adequate data to enable an assessment of these stocks. This paper presents the results of growth, catch curve and yield per recruit analyses from the monitoring programme conducted between 1993 and 1996. Preliminary results show that all of these stocks but sole in VIIb,c are over-exploited. TAC levels (based on reported catches in previous years) may be inappropriate for the current stock sizes. It is also important to compare biological characteristics between ICES Divisions to determine the appropriate assessment areas. Comparisons of biological parameters between areas have so far been inconclusive.
    • The Status and Management of Oyster (Ostrea edulis) in Ireland

      Tully, O.; Clarke, S. (Marine Institute, 2012)
      Fourteen oyster surveys were completed during 2010-2012 in 6 bays on the west coast of Ireland prior to and following annual late autumn fisheries. Vessel based surveys using locally designed dredges were undertaken using in Tralee Bay, Galway Bay, Kilkieran Bay, Clew Bay, Blacksod Bay and L. Swilly. Survey extent was defined by local knowledge of the distribution of beds in each bay and from previous survey reports. The extent of oyster beds, oyster densities, biomass, size composition and growth and mortality rates are reported. The governance and management of oyster fisheries in Ireland is described and conservation requirements for oyster habitat are discussed with reference to the EU Habitats Directive. Survey extents varied from 0.9-13km2. Population densities of oyster were generally <0.5 oysters m-2 but higher densities of up to 50 oysters m-2 occurred in areas of inner Tralee Bay. In other sites, densities did not exceed 5 oysters m-2. The majority of national oyster biomass occurred in inner Tralee Bay where biomass varied from 980-1330 tonnes in the 2010-12 surveys. Biomass in outer Tralee Bay and L. Swilly was approximately 100 and 124 tonnes, respectively. Biomass estimates in inner Galway Bay, Kilkieran Bay, Clew Bay and Blacksod Bay were all less than 50 tonnes. vonBertalanffy growth parameters, k and to, were 0.21year-1 and 0.23years respectively. These parameters were estimated from shell height frequency data and by fixing Linf at 120mm, based on the maximum size of oysters recovered during surveys. Total mortality rates (Z) were estimated from the linear portion of length converted catch curves using these derived growth parameters. Z estimates, in pre and post fishery surveys, averaged 1.07 and 1.30 respectively in 2010 and 0.94 and 1.55 respectively in 2011. Fishing mortality rate (F), derived from the difference in Z estimates in pre and post fishery surveys in inner Tralee Bay, was 0.9 representing an annual removal of 60% of oysters recruited to the fishery. Increase in biomass of a single cohort, simulated using derived growth rate parameters, the size weight relationship and different rates of natural mortality (M) suggests that maximum biomass develops prior to the minimum landing size of 76mm if M>0.4. Improved, site specific, estimates of growth and mortality rates and size at maturity data are needed to provide fisheries management advice for native oysters. Pacific oyster (Crassostrea gigas) was abundant and widespread, in what was previously Ostrea habitat, in L. Swilly. In some of these areas, Pacific oyster was the only oyster species present. In other areas both species co-existed although they were spatially segregated to a degree in relation to shore level.
    • The strategic importance of the fishing sector to rural communities and Ireland: a case study of the Rossaveal Region, Co. Galway

      Meredith, D. (Marine Institute, 1999)
      Fishing and ancillary industries are commonly perceived to be of significant social and economic value by virtue of their geographic location. Past socio-economic studies of fisheries and related industries largely confined themselves to analysing demographic statistics and relating these to official port fish landings data and descriptions of processing and ancillary industries. Despite these efforts, a clear picture of why and how fisheries are of socio-economic significance has not yet been achieved. As a consequence there is little de-tailed understanding of how ecological, legislative and market related changes impact on fisheries dependent communities. This study of the Rossaveal Region was funded by Marine Institute in an attempt to assess the importance of demersal, shellfish and pelagic fisheries to peripheral Irish communities.
    • A Survey of Nursery Grounds for Celtic Sea and VIIj Herring

      Clarke, M.; Egan, A.; Molloy, J. (Marine Institute, 2010)
      The need for a recruit index for the herring stock in the Celtic Sea and Division VIIj has long been recognised. In order to develop a survey for recruits and pre-recruits, good information on the distribution of these fish is required. This study is based on a pair trawl survey, conducted in February 2008. The area covered was from central-east Irish coast (Dundalk Bay) to central west Irish coast (Galway Bay), with special attention paid to the bays and inlets of the south and southwest coast. The overall aim was to map out the distribution of 0- and 1-ring herring so that decisions could be made on the design of a future survey for young fish. The catch was quantified and sorted according to species. Herring were sampled for length, weight, sex, maturity and age. Young herring appeared as a light dust on the 38 kHz frequency. The east coast of Ireland, from Dundalk Bay to Howth was identified as an important nursery area, though it was not possible to ascertain what proportion of these juveniles were of Celtic Sea origin. Within the Celtic Sea the main nursery grounds identified were Dungarvan Bay, Cork and Kinsale Harbours. All the bays surveyed in VIIj contained juvenile herring. Overall this survey was a success. It provided updated information on the occurrence of young herring along the coast. Along with information from fishermen, and literature sources it allows for the development of recruit surveys for herring of this stock. Further work remains to be done on discriminating the juveniles by season of spawning.
    • Using a multivariate approach to define Irish metiers in the Irish Sea

      Davie, S.; Lordan, C. (Marine Institute, 2009)
      There is an increasing need to take into account a “mixed fisheries” approach in management, assessment and sampling of fish stocks. To do this effectively it is necessary for groups of fishing trips with homogeneous fishing patterns or tactics to be defined into métiers. Presented here is the result of an Irish case study analysis in applying multivariate statistics to declared logbook landings to define Irish fleet métiers operating in the Irish Sea. Established multivariate statistical procedures, a combination of factorial and cluster analysis, were applied to five variables; landing profile, vessel length category, gear, mesh size range and month. The investigation has shown this methodology to be a suitable tool in identifying métiers without prior assumptions and enabled data to be described from a multivariate statistical perspective providing useful and informative results. In total twenty-two métiers were identified and defined from 2003 landings data, and a further 5 groups were formed to include trips which could not be assigned to a métier. Definitions were applied to 2003-2005 landings and effort data to examine their dynamics and stability. The dominant métier (in terms of effort and trips) contained high proportions of landed Nephrops taken by bottom otter trawlers using 70-89mm meshes. The effort in this métier was fairly stable over time. The greatest increases in effort and trip allocation occurred within métiers employing pots and traps for crustacean species. A small number of minor métiers (in terms of landings and effort) became obsolete over the three years examined. The effects of recent management measures are likely to have contributed to declines in the numbers of trips and effort in some métiers. For example, days-at-sea, limited mobile gears such as bottom otter trawls and beam trawls with ≥100mm mesh, have declined. Such changes within métiers over recent years have contributed to a deeper understanding of fleet dynamics in the Irish Sea. This analysis has identified and highlighted a segment of polyvalent Irish fishing vessels, which move between several métiers within a year. The definition of métiers can be used to enhance the Irish sampling programme in the Irish Sea by developing a finer scale, métier based, stratification of sampling. This in turn enables increased precision and robustness of national assessment data thus improving assessments and management advice. Defining métiers will prove advantageous in developing mixed fisheries assessments and advice.