• 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.
    • 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.
    • 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 abundance of boarfish (Capros aper) along the western shelf estimated using hydro-acoustics

      O'Donnell, C.; Farrell, E.; Saunders, R.; Campbell, A. (Marine Institute, 2012)
      The Boarfish (Capros aper, Linnaeus) is a relatively small deep bodied fish growing up to 23 cm in total length. Typically reddish in colour with large eyes and a highly protrusible mouth boarfish are known to inhabit shallow shelf seas to shelf slopes from 40-600 m. Boarfish are a mesopelagic shoaling species distributed in the eastern Atlantic from Norway to Senegal including the Mediterranean. Exploratory fishing for boarfish by Irish vessels began in the later 1980s when commercial quantities were encountered during the spring horse mackerel (Trachurus trachurus) and mackerel (Scrombrus scomber) fishery in northern Biscay. During the early 2000s the Irish landings were relatively small (<700 t per yr) and it was not until 2006 that a directed fishery developed in earnest. Landings peaked in 2010 at over 137,000 t prior to the introduction of TAC control and interim management plan. This survey represents the first dedicated exploratory acoustic survey for boarfish (Capros aper) undertaken along the western seaboard of Ireland. The survey was timed to coincide with peak spawning time as determined from histological analysis of commercial catch samples. Area coverage was based on the distribution of catches from the IBTS survey time series and from catch data from the pelagic fleet targeting boarfish since 2005. In total 3,160 nmi (nautical miles) of cruise track was undertaken by the MFV Felucca, over 32 transects relating to an area coverage of over 89,500 nmi². Coverage extended from the 50 m contour to the shelf slope (250 m). Transect spacing was set at 15 nmi throughout to make best use of the time available and the large geographical area to be covered. The results presented here are a composite of data collected during this survey and on the northwest herring survey (RV Celtic Explorer). Both surveys were timed to link up and were carried out over 33 days from north (59°N) to south (47°30’N). Acoustic data were collected using a Simrad EK 60 scientific echosounder via a Simrad ES-38B (38 KHz) split-beam transducer which was mounted within a tow-body. This configuration was calibrated on the survey vessel prior to departure. An age length key (ALK) compiled primarily from commercial samples collected during 2010 was applied during the analysis of survey data. Age distribution indicate that the stock was dominated by the following age classes in terms of abundance: 6, 7, 20+ and 9 year old fish and 20+, 9, 7 and 10 years in terms of biomass respectively. Immature fish from 0-2 years were poorly represented in survey catches and this is consistent with a spawning movement of mature stock away from feeding grounds on the shelf. During the survey boarfish shoals were primarily distributed along the shelf edge occurring as aggregations actively spawning or in a state of near readiness to spawn. As a result the abundance estimate is almost exclusively composed of mature individuals (>99%) which is in contrast to the primarily on-shelf distribution of commercial catches. The biomass and abundance estimates presented here were calculated using a modelled TS-length relationship, from as yet unpublished data for boarfish and applied retrospectively to acoustic data.
    • A History of common carp Cyprinus carpio (L.) in Ireland: A Review

      Brazier, B.; Caffrey, J. M.; Cross, T. F.; Chapman, D. V. (Marine Institute, 2012)
      This paper represents the most comprehensive and detailed summary of the history of common carp Cyprinus carpio (L.) in Ireland to date. It charts the earliest known introductions of the species to Irish waters, the rise in popularity of recreational angling for the species from c. 1950 onwards, the work carried out to establish the species in Ireland and explains the primary causes of their more recent distribution increase. Much of the historical research material gathered on common carp in Irish waters, including the first recorded details of introduction, is presented here for the first time.
    • 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.
    • Application of EDA (v 2.0) to Ireland: prediction of silver eel Anguilla anguilla escapement

      de Eyto, E.; Briand, C.; Poole, R.; O'Leary, C.; Kelly, F. (Marine Institute, 2016)
      Eel Density Analysis (EDA) is a modelling framework that can be used to estimate eel populations in aquatic habitats. Survey data (primarily electrofishing operations) are used to build predictive models describing the presence/absence and the density of eel. These models are then applied to the entire network of aquatic habitat in the area of interest to estimate the total population size. The fluvial (riverine) population of yellow eel in Ireland was estimated using the EDA (v2.0) model (Jouanin et al., 2012). A total fluvial population of 8,032,834 yellow eels and 200,821 silver eels (using a silvering rate of 2.5%) was estimated for 2011. Eel presence and abundance decreased as the distance to the sea increased, and the percentage of calcareous geology in the catchments decreased. Stock indictors (B0, Bbest and Bcurrent) were calculated from these yellow eel estimates to enable the display of precautionary diagrams for each EMU in Ireland. Lake production was also calculated for 2011, using empirical data from a small number of catchments. A precautionary diagram for this total production (fluvial and lacustrine habitat) is presented, and compared with previous estimates of stock indicators for Ireland.