Shark Depredation and Unwanted Bycatch in Pelagic Longline

Appendix 9
USA Atlantic, Gulf of Mexico and Caribbean
Pelagic Longline Swordfish and Tuna Fisheries:
Industry Practices and Attitudes towards Shark Depredation and Unwanted Bycatch
John W. Mandelman and Tim B. Werner, New England Aquarium, jmandelman@neaq.org,
twerner@neaq.org
A9.1. Introduction
It is widely held that the incidental capture of sharks in fisheries
targeting alternative species represents a massive challenge in the
proper management of this group (Figs. A9.1 and A9.2) (Barker and
Schluessel, 2004). Akin to the outcome in high-seas commercial
fisheries around the globe, sharks compose the highest percentage
of bycatch in the U.S. Atlantic PLL (PLL) fishery for swordfish, tunas
and tuna-like species (Beerkircher et al., 2002). Although rarely
targeted in U.S. domestic PLL operations, sharks and rays constituted
25% of the overall catch in this fishery between 1992 and 2003
according to observer data (Abercrombie et al., 2005). If accounting
for the other foreign fleets pelagic longlining in Atlantic waters, it
has been estimated that the extent of shark bycatch by this capture
method is considerably high, rivaling both the Indian and Pacific
in terms of the number of individuals and overall shark biomass
taken (Bonfil, 1994). Sharks are also among those responsible for
inflicting damage (depredation) to baits, gear, and hooked targeted
catch prior to haul-back in this fishery (Hoey and Moore, 1999). The
species most commonly encountered in PLL operations are a variety
of carcharhinids, and to a lesser extent, lamnid sharks. As several
of these species are either prohibited from being landed or lack
appreciable commercial value, discard rates are chronically high. For
these reasons, interactions with sharks in the domestic PLL fishery
are presumed as a relative nuisance; encumbering commercial
operations for tuna and swordfish and afflicting fishermen with
considerable costs through losses of and damage to gear, target catch
(via depredation) and time.
At the same time, physiological stress and physical trauma imposed
during capture and handling can compromise the ultimate survival
of discarded shark bycatch (Bonfil, 1994; Berkeley and Campos, 1988).
If coupled with directed landings, discard mortality can elevate
total fishing mortality (F) and imperil shark populations around
the globe (Musick et al., 2000). The control of unintended shark
Fig. A9.1. Longline captured
Isursus oxyrinchus (shortfin mako
shark), just prior to boarding.
(Photo courtesy of Greg Skomal,
Massachusets Division of Marine
Fisheries, USA.)
Fig. A9.2. Longline captured
Prionance glauca (blue shark), just
after boarding. (Photo courtesy of
Greg Skomal, Massachusets Division
of Marine Fisheries, USA.)
interactions is thus important not only for the operations of the
longline fishing industry, but the health of interacting shark
populations. Importantly, bycatch issues have been the basis of
several regulatory measures imposed upon the Atlantic PLL fleet.
It is therefore clear that mitigating the extent of incidental takes in
this fishery, inclu-ding those with sharks, will behoove industry,
management and conservation communities alike.
In the following report, we address the estimated extent of shark
bycatch, the species composition of this catch, and to a much lesser
extent, shark depredation in the PLL fishery of the Atlantic, Caribbean
and Gulf of Mexico (GOM). We also present ongoing research and
potential strategies regarding the attenuation of shark interactions in
this fishery. In doing so, several important factors regarding the data
sources must first be addressed.
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