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.
