The seasonal variation of trawl cod-end selectivity and the role of learning in mesh penetration behaviour of fish
Başlık çevirisi mevcut değil.
- Tez No: 400712
- Danışmanlar: DR. CHRIS GLASS, DR. MONTY PRIEDE
- Tez Türü: Doktora
- Konular: Balıkçılık Teknolojisi, Fisheries Technology
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: İngilizce
- Üniversite: University of Aberdeen
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Balıkçılık Temel Bilimler Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 231
Özet
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Özet (Çeviri)
The work carried out in this thesis aimed to improve the understanding of effects of season and learning capabilities offish on trawl cod-end selectivity. To investigate the seasonal variation in codend selectivity, three sea trips were carried out on board a Scottish commercial trawler. Experiments were performed on the same grounds using the same fishing gear with an improved covered cod-end technique. The target species was haddock (Meianogrammus aeglefinus). Sea trips were conducted in April 1995 (post-spawning stage), September 1995 (after summer feeding) and February 1996 (pre-spawning stage). Selectivity parameters were estimated haul by haul for each season by a generalised linear model with logistic link. The 50% retention lengths (L5o) for each cruise were found to be significantly different. The selectivity was poorest in post-spawning stage in April (LJO-27.7cm), the highest after summer feeding in September (Lj0-33.4cm) and intermediate at pre-spawning stage in February (Lso^S 1.2cm). There were differences in the length-girth relationship of the haddock between the three cruises. However, the variation in selectivity between seasons cannot be explained by the variation in girth alone. The lowest Lsooccurred when girths at a given length were smallest in April. Girth measurements were obtained in September 1995 and February 1996 allowing the selectivity parameters to be estimated in terms of girth. The 50% retention girth (G50) in September (G5o= 177mm) was significantly higher than that in February (G50= 159mm). One of the potential reasons for this variation is expected to be due to the effect of the water temperature on the maximum swimming performance of fish. Water temperature on the fishing ground was 12 °C in September and 7 °C in February and April. Laboratory experiments to predict the maximum swimming speeds of haddock and whiting {Merlangius merlangus) from the minimum muscle contraction time of the fish, when stimulated by an electric pulse, showed a significant increase of the maximum swimming speed at 12 °C in comparison to 7 °C. For example, the maximum predicted tail beat frequency of 30cm haddock was 12.9Hz in 7 °C whereas it was 40% higher, 18.1Hz, in 12 °C. The maximum observed swimming speeds of haddock and whiting while being raced between two flashing lights in a 6m length tank were respectively 52.4% and 20.7%, higher at 12 °C than at 7 °C. Similarly, average time taken to complete first tail flip at the start of escape response for haddock was more than 50% longer at 7°C than in 12 °C. Decrease in the weight of a given length of fish during spawning showed that the number of individual fish needed to fill the same amount of quota is much greater in April than in September. For example 32.4% more 40cm haddock must be caught to achieve the same quota in April than in September. The effect of learning in mesh penetration behaviour of haddock, whiting and saithe {Pollachius virens) was investigated under laboratory conditions. This study demonstrated that the fish were able to leam certain tasks and they were reluctant to penetrate mesh barriers. However, their speed of response increased with increasing experience.
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