Survival of Atlantic Cod (<i>Gadus morhua</i>) in the Northwest Atlantic Longline Fishery

Abstract

Longline fishing has often been promoted as a clean, low impact fishing method. Some longline fishermen and biologists have expressed concern that there is a high mortality rate for cod and haddock that pass through a dehooking device prior to release. The device, aptly called the “crucifier,” usually consists of two steel cylinders placed vertically on the gunwale of the vessel. During hauling, the gear passes through the opening between the cylinders white the fish, too large to pass through the narrow opening, is excluded. This process pulls the hook from the mouth of the fish and can inflict severe injuries such as torn and broken jaws.A study was conducted to determine the survival rate of sub-legal cod caught in the longline fishery using 11/0 circle hooks. The focus of the research was to assess the rate of mortality of sub-legal catch after the cod were placed in cages for 72 hours. The results of the study showed that there was high mortality (69%) associated with capture using the 11/0 circle hook when the fish were injured by the process of having the hooks removed from their mouths by the crucifier. Furthermore, sublegal cod that had wounds from the dehooking process and were under 39 cm were statistically more likely to die as compared to cod between 38 and 49 cm.An ancillary set of observations on the predation by sea birds of released sublegal cod was included. Despite low numbers, the findings from these observations show that sea bird predation should be included when estimating the survival offish caught by a longline.