Observations by Divers on the Survival of Tagged and Untagged Haddock Melanogrammus Aeglefinus(L.) After Capture by Trawl or Danish Seine Net

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Abstract
The physiological factors affecting the survival of demersal fish caught by trawl and Danish seine were considered in relation to initial tagging mortality. Experiments using haddock that were confined in sea-bed cages showed that the initial mortality was greater when the fish had been taken to the surface after capture than when they were transferred directly from the codend to a sea-bed cage. It is probable that the main factors responsible for causing initial mortality in those fish that had been taken to the surface were physiological shock and fatigue together with swimbladder damage; together these factors rendered the fish extremely vulnerable to any adverse environmental conditions when they were returned to the sea-bed. Tagging itself was considered to be a comparatively minor contributant to initial mortality.

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