Objective
1. To provide quantitative measurements of dominant factors which cause variability in trawl codend selectivity in Baltic cod fishery, and to develop codend modifications and operational approaches that will improve trawl size-selection relative to present designs.
2. To develop, test and apply improved methodology for estimating the escape-survival of cod under commercial fishing conditions, and to identify codend designs that may enhance survival.
3. To develop a model for assessing biological and socio-economic consequences of improved selectivity in the Baltic fishing fleet.
The top-panel window codends showed higher L50-values than the corresponding standard codends. In window codends a pronounced positive correlation was observed with L50 and selection range (SR). The confidence regions, however, were relatively large for the 125 mm and 135 mm window codends.
The codend without the cover caught on average 15% more cod than the codend with the cover. The variation in catches between the hauls, however, was fairly large. The codend with the cover caught significantly less cod below 45 cm than the codend without the cover. The hauls made without the cover had a substantially larger variability in individual selection curves, and L50 and SR of the combined hauls were higher.
A large between-haul and between-vessel variability in selectivity was obtained in vessel-size experiments. Vessel-size, however, was not found to have any clear effect on the L50.. On the other hand, indications were obtained that vessel hauling technology can be a potentially important factor causing variability in selectivity. The best selectivity in terms of L50 was found on a side trawler. This difference is likely connected to the duration the gear is slack during the haul-back. Indication of a negative correlation with catch size and L50 was obtained.
A slightly higher survival was obtained in the Ultra-Cross window codend escapees (99.2%) than in the Danish exit window codend escapees (94.6%). Generally, the survival of trawl escapees was very high. No seasonal or catch-size effect in mortality was noticed. It is noteworthy, however, that hauls were conducted with fairly small catches in 1998.
Fish length was the main factor affecting to the probability of fish to be injured; the bigger fish the more probably it will have an injury. Fish escaping from a conventional diamond mesh codend had a higher injury probability than those escaping the Danish exit window codend. Codend catch (kg) affected negatively to the injury probability and in particular to net marks and bleeding lesions. Water temperature affected strongly and positively to the scale loss probability but had no effect on bleeding lesions.
The Turned-Mesh-Codend configuration appeared to be a simple and efficient way to open the codend meshes and improve the codend selectivity. More experience and data, however, are required for final conclusions. Possibilities to improve the on-deck handling should be investigated.
Description of work
The project consists of the following specific tasks:
Task 1.1. Development of a new cod-end cover
Task 1.2. Development of methodology for assessing fish survival
Task 2. Assessment of optimal window position and window/codend mesh size
Task 3. Effect of season, vessel-size and vessel-gear interaction on selectivity
Task 4. Effect vessel type/hauling technology on selectivity
Task 5. Escape mortality and skin injury of cod under commercial fishing conditions
Task 6. New innovative codend designs
Task 7. Data processing
Task 8. Modelling of biological and socio-economic impacts
Task 9. Project management and technology transfer
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- agricultural sciences agriculture, forestry, and fisheries fisheries
- social sciences sociology demography mortality
- natural sciences computer and information sciences data science data processing
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Coordinator
00721 HELSINKI
Finland
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