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Selectivity and Survival of Atlantic Cod (Gadus....
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GRANT NUMBER:  NA66FD0028           NMFS NUMBER:  95-NER-141

REPORT TITLE:  Selectivity and Survival of Atlantic Cod (Gadus morhua) and Haddock (Melangrammus aeglefinus) in the Northwest Atlantic Longline Fishery

AUTHOR: Marianne Farrington, Henry Milliken, Emily Lent and H. Arnold Carr

PUBLISH DATE:  1998

AVAILABLE FROM:  National Marine Fisheries Service, Northeast Region, One Blackburn Drive, Gloucester, MA 01930.  TELEPHONE:  (508) 281-9267

ABSTRACT

Longline fishing has been touted as a clean fishing method which does not impact the substrate. However, some Longline fishermen and biologists have expressed concern that there is a high mortality rate for cod and haddock that, prior to their release, pass through a dehooking device aptly called the "crucifier".  This apparatus is typically composed of two parallel steel cylinders placed vertically on the gunwale. The hooked fish on the longline encounters the crucifer during the hauling of the gear and the hook is pulled from the fish as it passes through the crucifier. This process can inflict severe injury to the mouth of fish. Two studies were conducted. The first study compared the length frequencies of cod caught on 11/0 vs. modified 15/0 circle hooks. The 15/0 circle hook was non-traditional because it was constructed out of the same gauge wire as the 11/0 hook. This study found that the 15/0 circle hook retained the same number of legal cod yet caught few sublegal cod.

In the second study, juvenile cod were collected during experimental longline fishing operations during 1996 and 1997. Fish were removed from fishing gear either mechanically (Wounded) or gently by hand (TLC). Survival rates were determined by placing the juvenile fish into large cages and returning them to the depth at which they were caught for a period of about 72 hours. The lowest survival figures were found for fish that were wounded by the mechanical dehooking device. The focus of the research in the second study was to assess the longline fishery and the rate of mortality of sublegal catch after the fish were placed in cages for 72 hours. The results from the study showed that there was high mortality associated with capture using the 11/0 circle hook when the cod were damaged form the process of having their jaws broken or torn after passing through the crucifer. Mortality increased when predation by herring gulls was considered.

 
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