Shark Depredation and Unwanted Bycatch in Pelagic Longline

Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries
Pelagic longlining occurs throughout the world’s oceans, has been
used since the nineteenth century, and ranges from small-scale
domestic artisanal fisheries with small sometimes open vessels
to modern mechanized industrialized fleets from distant-water
fishing nations with large vessels. Pelagic longlines, where gear is
suspended from floats drifting at the sea-surface, mainly target large
tunas (Thunnus spp), swordfish (Xiphias gladius), other billfishes
(Istiorphoridae spp), and dolphin fish (mahimahi) (Coryphaena
spp), can be up to 100 km long and carry up to 3,500 baited hooks
(Brothers et al., 1999).
Much progress has been made to identify effective, commercially
viable, and even operationally beneficial methods to significantly
reduce seabird and sea turtle bycatch in longline fisheries (Gilman et
al., 2003, 2005, 2006b, 2007; Watson et al., 2005). Bycatch of seabirds
and sea turtles in pelagic longline fisheries poses a substantial threat
to some albatross, large petrel, leatherback sea turtle (Dermochelys
coriacea) and loggerhead sea turtle (Caretta caretta) populations
(Brothers et al, 1999; FAO, 2004a,b; Gilman, 2001; Gilman et al., 2005,
2006a,b). Relatively little progress has been made to reduce cetacean
and shark interactions in longline fisheries (Gilman et al., 2006d).
In some pelagic longline fisheries, especially in fleets that have
restrictions on shark finning, unwanted shark bycatch and depredation
pose substantial ecological, economic, and social problems.
As demonstrated in some fisheries to address seabird and sea turtle
bycatch (Gilman et al., 2005, 2006b; Martin et al., 2006), collaborative
approaches, which tap fishers’ large repository of knowledge, may
likewise successfully reduce unwanted shark interactions.
Fig. 1.1. Generalized configuration of pelagic longline gear.
Fig. 1.1 shows a generalized configuration of pelagic longline gear.
However, the gear design, including lengths and materials of float,
main, and branch lines; number of hooks between floats; amount
and placement of weights on branch lines; depth of gear; and types
of hooks and bait; as well as methods of setting and hauling, will
vary between fisheries, between vessels in a fishery, by season and
fishing grounds for an individual vessel, and even within the gear of
an individual vessel.
We collect information from longline industries ranging from smallscale
artisanal fisheries to large-scale industrial distant water fleets
to obtain a more complete understanding of shark-pelagic longline
interactions, current fisher attitudes and practices employed in
response to shark interactions, identify methods to avoid shark
interactions, identify research priorities and assess the effects of
legislation that affect longline practices in catching and processing
sharks. Information on existing fisher knowledge and new strategies
for shark avoidance may benefit sharks and fishers wanting to
reduce shark interactions. Improving the understanding of longline
industry attitudes and practices towards shark interactions provides
industry and management authorities with better information to
address these problems.
Table 1.1. Number of people by employment status interviewed in 12 fisheries included in the study of shark depredation and bycatch in pelagic longline
fisheries.
Employment
Category of
Interviewees
Captain
(Skipper)
or Fishing
Master
Vessel or
Company Owner
(Non-Captain)
Australia
Longline Tuna
and Billfish
Fishery
Chile
Artisanal
Mahimahi and
Shark Fishery
and Swordfish
Fishery
Number People Interviewed
Fiji
Longline Tuna
Fishery
Italy
Mediterranean
Industrial
Longline
Swordfish
Fishery
Japan
Distant Water,
Offshore and
Nearhsore
Longline
Fisheries
Peru
Artisanal
Mahi Mahi
and Shark
Fishery
South
Africa
Longline Tuna
and Swordfish
Fishery
USA Hawaii
Longline
Tuna and
Swordfish
Fisheries
11 13 5 17 19 16 10 10
3 2 1 0 2 0 0 0
Crew 0 7 0 0 1 26 0 2
Fishing
Cooperative
Representative
0 0 0 0 3 0 0 0
Port Official 0 0 0 0 1 0 0 0