GRANT
NUMBER:
NA57FD0031
NMFS NUMBER:
REPORT
TITLE:
Reduction of Bluefin Tuna and Undersize Swordfish Bycatch
in Atlantic Longline Fisheries
AUTHOR:
Steven
A. Berkeley and Randy E. Edwards
PUBLISH
DATE:
AVAILABLE
FROM: National
Marine Fisheries Service, Southeast Region, 9721 Executive
Center Drive, North Koger Building, St. Petersburg, FL
33702. PHONE: (813) 570-5324
ABSTRACT
There
were two primary objectives of this research: (1) to determine
times, depths, areas, temperatures, and water temperature
profiles of the water mass associated with longline catches
of yellowfin tuna, bluefin tuna, undersize swordfish,
and other bycatch species; and (2) to determine the feasibility
of using lighter test leaders to allow giant bluefin tuna
to break free while still retaining target species.
When
this proposal was submitted, the southern incidental bluefin
tuna quota was being taken annually, usually within 3
or 4 months, after which bluefin could no longer be legally
landed. This meant that bluefin caught after the closure
were being discarded, frequently dead. The depressed
condition of the bluefin stock meant that these discards
represented a significant loss to the spawning stock and
potential for recovery as well as a substantial economic
loss to the fishery. However, in recent years, either
due to changes in regulations or because of reduced abundance,
the quotas have not been taken, and discards have been
minimal. During the course of our MARFIN project we encountered
only a single bluefin tuna in 61 sets of longline gear.
Because of the rarity of bluefin encounters, and thus
the near elimination of the discard problem, it was impractical
for us to pursue objective 2 of the original proposal.
Although we designed and tested a "weak link"
system that would have allowed us to test various strength
leader material without losing any fish as a result, we
never conducted these experiments.
The
investigators attached "hook timers" to gangions
and time--depth recorders to the mainline of longlines
deployed by cooperating yellowfin tuna fishermen operating
in the Gulf of Mexico. In addition, expendable bathythermographs
were deployed at the start and end of each set and haulback
to characterize the thermal structure of the water column.
These instruments allowed the investigators to identify
the time, depth, and water temperature in which hookups
occurred. Up to 43 nautical miles of mainline were
deployed, with soak times of over 24 hours. By understanding
the fishing operation, the investigators were able to
develop gear and attachment techniques that did not interfere
with or slow down the commercial fishing operation.
