International Program of Standardised Trawl Surveys
| Other titles | Programme International de standardisation de campagnes de chalutage | ||||||||
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| Type | Report | ||||||||
| Date | 2001-07 | ||||||||
| Language | English | ||||||||
| Ref. | CONTRACT REFERENCE DG XIV STUDY CONTRACT 98-057 | ||||||||
| Author(s) | Mahe Jean-Claude1 | ||||||||
| Contributor(s) | Bellail Robert | ||||||||
| Mot-Clé(s) | mer d'Irlande, mer Celtique, indices d'abondance, performance technique, stratégies d'échantillonnage, distribution des espèces, coefficients de conversion, calibration d'engins, campagne de chalutage, chalut de fond | ||||||||
| Keyword(s) | Irish sea, Celtic sea, abundance indices at age, gear performance, sampling stratégies, species distribution, conversion coefficients, gear calibration, trawl surveys, bottom trawl | ||||||||
| Abstract | The IPROSTS project had two main objective : - Completionn of research vessel surveys in the autumn of 1999 and 2000 in ICES areas VI, VII and VIII in order to provide abundance indices at age for the major commercial species exploited in these areas, - Standardisation of the methodology used in bottom trawl surveys.For completion of the first objective, the French Research institute IFREMER conducted surveys in the Celtic Sea and the Bay of Biscay on board the Research Vessel, Thalassa. The Marine Institute of Dublin conducted surveys in the Irish Sea and Celtic Sea on board the Research Vessel Celtic Voyager and in the Western area of Ireland on board two chartered commercial fishing vessels (Marliona and Shauna Ann). The Marine Laboratory of Aberdeen conducted suveys in subareas Via, northern Irish Sea and northern part of subarea VIIb on board the research vessel SCOTIA. The SCOTIA and THALASSA used standard GOV bottom trawl, the Celtic Voyager a GOV designed bottom trawl but smaller, adapted to the size of the vessel. The commercial fishing vessel used Rock hopper commercial gear fitted with a 20 mm codend liner.From the data collected, time series of abundance indices at age were completed to be used as tuning indices in Assessment Working Groups.Regarding the second objective, two field of study were identified. The first is related to gear performance.The first question is are research vessels fishing together with similar gear getting similar catches. To answer this question, two intercalibration experiment were undertaken between the SCOTIA and CELTIC VOYAGER and between theTHALASSA and CELTIC VOYAGER. Initially intercalibration was also planned between the Irish Research and commercial vessels but a national decision was taken after the start of the study to build a new ship to undertake the surveys in the area covered with the commercial vessel. It was therefore decided to abandon this part and to carry the intercalibration with the new vessel when she is on duty. The analysis showed that there was no statistical evidence to support the hypothesis that the catches were different. The second question considered whether, on a single vessel using the same gear, gear performance varies in relation to external factors and whether or not this affects catchability. Conclusions were that all surveys produced major depth related changes in gear performance and that each net, including those of identical construction, display individual gear geometry; this may have an effect on the catch performance.The second field of study was sampling strategies. A study was undertaken on sampling for age and showed that optimisation can be achieved by choosing the strategy adapted to the biological characteristics of the target species. Finally from the hydrological data collected during the SCOTIA and THALASSA surveys, hydrological maps of surface and bottom temperature were produced. |
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