Irish Fisheries Investigations: Recent submissions
Now showing items 21-28 of 28
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The Dundalk Cockle Cerastoderma edule Fishery in 2003-2004A cockle fishery in Dundalk Bay has been infrequently documented since 1970. Cockle bearing sands and muds are 44.5 km2 in extent. The bay, which is in an SPA and a cSAC also supports large numbers of overwintering birds, of particular relevance is the oystercatcher (Haematopus ostralegus). In 2003 and 2004 when an assessment of the fishery was undertaken, cockles ranged from 0 to 8+ years of age, but the vast majority were 0 and 1+ animals. Growth was rapid and 53% of asymptotic length (49.1 mm) was achieved at the first winter. In agreement with observations elsewhere, the density of the rapidly growing animals was very low. The estimated cockle biomass in spring 2004 was 1,654 tonnes comprising 143 million animals. A survey undertaken in spring 2004, suggested that spat falls contributing to the population may not have been evenly distributed throughout the Bay. Condition factor in 2003 and 2004 did not conform to an expected seasonal pattern, suggesting that some parts of the area supported better growth rates than others. Cockle landings from this fishery are of good quality. Cockle size is at the upper end of the range in Britain and Ireland and the majority of individuals landed by suction dredging were 1+ years old. Raked landings contained more 2+ cockles than suction-dredged ones. Damage to cockles discarded by suction dredging followed the pattern reported elsewhere and damage rates increased with the size of the animals. Some cockle landings have probably always been made in Dundalk Bay by picking and raking, but 2001 marked the beginning of an expansion of the dredge fishery, whose landings exceeded 200 tonnes in 2004. The necessity for controls and management of this fishery in the context of EU legislation and particularly within the constraints of the Habitats Directive is briefly examined.
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Fishery Associated Changes in the Whelk Buccinum undatum Stock in the Southwest Irish Sea, 1995-2003The whelk fishery of the southwest Irish Sea had a turnover of approximately €18 million and employed 250 people directly and indirectly in catching and processing in 2003. In the nine years, 1995-2003 inclusive, whelk landings to Ireland from the southwest Irish Sea fluctuated between 3,800 and almost 10,000 tonnes(t) per year; from an estimated 5,000 – 15,000 boat-days annually. A collapse in landings was recorded in 1997 and again in the spring of 2004. The fishery is divided for assessment purposes into four sectors, the central two consisting largely of nursery area and the north and south extremities of the fishery populated by more older, larger and mature whelk. Logbooks were not completed by fishermen participating in this fishery which was, in theory, managed by size limit, but the regulations were not enforced. Boats fishing whelk made daily fishing trips and daily weights recorded by processors were used to estimate biomass in each of the sectors by depletion regressions. Total biomass fluctuated between 12,720 t in 1999 and 37,319 t in 2002. The estimates based on a full season’s landings are used to compare the fishery from one year to the next and to supply weighting factors for other parameters of the population. Exploitation rates were lowest in one of the central sectors of the fishery (where they averaged 27% annually). At the southern extremity they averaged 39%. Depletion estimates based on landings records from approximately April to 15 June provided higher exploitation rates and lower biomass. The mortality coefficient Z, calculated from a catch curve, peaked in two years, 1998 and 2002, as did an index of recruitment. The age at full recruitment declined after 2000. Throughout nine years of documented history, one of the central sectors of the fishery assumed progressively greater dominance over the others, providing 77% of the landings from the entire fishery to its ports in 2003. Some sectoral changes to the whelk population may be irreversible: the oldest animals have been removed from the northern extremity of the fishery and while the whelks which are exploited at the southern end between 2000 and 2003 were similar in size to those exploited in the mid-1990s, their tonnage between 1999 and 2003 decreased from 47 to 4% of the landings in 1995. A substantial recruitment in 2001 or 2002 was followed by an increase in fishing effort of 42% between 2002 and 2003 and this is identified as the reason for the collapse in 2004.
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An Atlas of Fishing and Some Related Activities in Ireland's Territorial Sea and Internal Marine Waters with Observations Concerning their Spatial PlanningThis Atlas was initiated as part of Ireland's preparation for the Water Framework Directive (WFD) which, inter alia, required mapping the distribution of mobile fishing gears in coastal waters (inside 1 n mile outside the base lines). The Atlas subsequently expanded the geographical extent of the review out to 12 n miles. The history, descriptive terminology and extent of subdivisions of the territorial sea are provided. The Atlas is a collection of 1,885 polygons showing the distribution of fishing and fishery related activities, including aquaculture and mariculture within the Republic of Ireland's territorial sea and internal marine waters. The Atlas demonstrates that the greatest range and intensity of fishing and related activities are undertaken in the internal waters of the State. Hook and line fishing emerged as the most widely used metier and a combined array of mobile gears, ranging from pelagic otter trawls to hydraulic dredges, took second place. The total area occupied by fishing and fishing related activities was just under 125,000 km2. The principal metier groupings within 12 n miles were: hook and line occupying 57,000 km2 (45% of the total), mobile gears (towed enclosing nets and dredges) accounting for 27,530 km2 (22%). Passive nets (static tangle and gill nets and the now defunct salmon drift nets) made up 18,000 km2 (14%). Pots targeting crustaceans and molluscs occupied 13,250 km2 (11%). Aquaculture and mariculture occupied 172 km2, some 0.4% of the area within 12 n miles. To supplement the polygons, a table of metier and species combinations in internal and territorial waters opposite each county with a long shoreline is supplied. The table includes fisheries whose existence is known but not their extent. The consequences for benthic community structure of the use of a particular metier, the purpose of the exercise for the WFD, are considered. "Community" refers to fish or invertebrate species assemblages. Applications for the data are discussed in the context of a growing appreciation of the need to plan the use of inshore waters for fishery conservation and to accommodate a wide range of stakeholder interests and to embrace the ecosystem approach to maritime governance. Difficulties inherent in conserving fish species rather than biological communities are illustrated by reference to a case history. Data presented in the document were sourced from the tacit knowledge of stakeholders. Planning jurisdiction in the Republic of Ireland is described with reference to inshore waters. Recent thinking by fishery commentators is reviewed. Finally, current thinking on inshore spatial planning within the EU and particularly among our nearest neighbours is discussed and the possibility of implementing ICZM is briefly considered. This document is presented as Version 1 of a continuing exercise. Governmental departmental arrangements and collected data refer to the period up to 2006. The Atlas should be periodically revised as more information becomes available.
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An Acoustic Survey of Orange Roughy Aggregations to the West and North of the Porcupine BankThe survey was carried out over a 14 day period from the 5th – 20th February 2005 onboard the 65m RV Celtic Explorer. The main focus of this pilot survey was to acoustically survey orange roughy (Hoplostethus atlanticus) spawning aggregations.
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F-Press: A Stochastic Simulation Tool for Developing Fisheries Management Advice and Evaluating Management StrategiesF-PRESS is a stochastic simulation tool based on a simple algorithm designed to fit in with the ICES conceptual framework for software development. F-PRESS can be used to develop probabilistic assessment advice or to evaluate management strategies or harvest control rules (HCRs). In this paper, we describe and justify the underlying methodology on which F-PRESS is based and give full details of the modular structure of the simulation algorithm. We use the example of Irish Sea cod to demonstrate how the software can be used to develop probabilistic management advice or to evaluate and compare different HCRs.
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The Japanese Bluefin Tuna Longline Fishery in the Northeast Atlantic: Report of an Irish ObserverThis paper describes an observer trip on a Japanese freezer longliner in the international waters of the North East Atlantic in the autumn of 1997. The observation period was 71 days during which 7 species were recorded as catch and bycatch from 57 sets. Although bluefin tuna was the target species, with 18,894kg gilled and gutted weight (GWT) caught, the most frequently retained species was blue shark, Prionace glauca, followed by bluefin tuna. Three shortfin mako shark, Isurus oxyrinchus, one swordfish, Xiphias gladius and one anglerfish, Lophius spp., were also recorded. The most frequently discarded species were lancetfish Alepisaurus ferox, and deal fish Trachipterus arcticus. Bluefin tuna ranged from 139cm to 275cm in fork length (FL) and from 64kg to 347kg in round weight (RWT) with clear modes of 190cm and 136kg. Recent ageing results from the North East Atlantic infer ages of 4 to 17 years old. CPUE was lower than Norwegian sponsored trials in the North East Atlantic in 1998 and similar to those computed by the Japanese longline observer programme in 2000, 2001 and 2002. There was no evidence of trend in bluefin CPUE over the course of the observation period. The modelled length weight relationship predicted higher values than established length weight relationships for bluefin tuna in the East Atlantic: ICCAT modelled RWT for East Atlantic bluefin was 87% of the observed round weight and 90% of the predicted RWT value for Koshin Maru #8 tuna. Over the observation period the condition of bluefin tuna was found to decline and examination of stomachs showed that most were empty or contained low numbers of prey items. Declining condition factors and apparent scarcity of prey are discussed in the context of CPUE. Prey scarcity reflected in declining condition may increase the effectiveness of baited hooks causing abundance estimates derived from CPUE series to over-estimate the population of bluefin tuna in the North East Atlantic. Investigation of condition indices has the potential to estimate stock ratios in longline catches in the North Atlantic. All observed blue shark catch were female with lengths ranging from 140cm to 250cm.
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Using a multivariate approach to define Irish metiers in the Irish SeaThere 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.
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A Survey of Nursery Grounds for Celtic Sea and VIIj HerringThe 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.