Shark Depredation and Unwanted Bycatch in Pelagic Longline

Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries
A9.1.1. Caveats in available data sets and reports
As recently as a decade ago, quantifying the extent of global shark
bycatch and its impacts on population abundances was under-analyzed
and viewed as an uncertain proposition (Bonfil, 1994). Although not
to the same extent as with cetaceans and sea turtles, management
and conservation attention dedicated to incidental shark interactions
in the U.S PLL fishery has heightened in recent years, providing the
impetus to propagate a variety of reports, peer-reviewed publications,
and documents addressing shark bycatch in this fishery. Recordings of
shark landings and discards that constitute these reports/publications,
such as those submitted to The International Commission for the
Conservation of Atlantic Tunas (ICCAT), have been derived from a
variety of data sources that were being collected prior to the onset of
enhanced attention towards sharks. In relation to the U.S domestic
fishery, these include dealer reports, tournament and weigh-out
records, canvas data and most extensively Pelagic Observer Program
(POP) data (since 1992) and mandatory fishermen logbook data
(since 1982). Additionally, the Canadian Observer Program has also
recorded catches in the Northernmost Atlantic. Despite attempts by
certain authors to reconcile these data, the diversity in the reporting
sources and multitude of confounding fishing, geographical, and
reporting variables have limited the scope in or complicated the
ability to draw sound conclusions (Crowder and Myers, 2001). In
addition, the lack of emphasis on sharks in earlier years presumably
resulted in more cases of non-reporting and misidentification.
Additional confounding variables include the large geographic region
encompassing the reporting areas, shifts in gear regimes, regulatory
transitions, diversities in fishing strategies and/or target species,
skewed data from disproportionately high sharks takes from limited but
often uncharacteristic (and under-described) sets/conditions
(Hoey and Moore, 1999), and in relation to abundance trends, the
uncertainty in the rates of discard mortality for sharks following
longline capture (Bonfil, 1994). As distinguishing between the possible
species accountable for depredated target catch and/or bait is not
always possible, establishing the rates of shark depredation in the PLL
fishery has also proven irresolvable in associated reporting (Lawrence
Beerkircher, personal communication).
a) swordfish;
b) billfish;
c) yellowfin, bigeye
and bluefin tuna;
d) other tunas;
e) sharks and rays;
f) unknown species;
g) finfish;
h) marine turtles,
marine mammals
and birds
Fig. A9.3. Catch reported by scientific observers on U.S. longline vessels
to the U.S. National Marine Fisheries Service Southeast Fisheries Science
Center, 1992-2003 (Abercrombie et al., 2005).
Fig. A9.4. Eleven areas used in analysis of the U.S. North Atlantic longline
swordfish logbook data (PLTRT, 2006). CAR = Caribbean; GOM = Gulf of
Mexico; FEC Florida East Coast; SAB = South Atlantic Bight; MAB = Mid
Atlantic Bight; NEC = Northeast Coastal; NED= Northeast Distant;
SAR = Sargasso; NCA = North Central Atlantic Tuna; TUN = North;
TUS = Tuna South.
Finally, many of the available documents have mined data from periods
prior to the recent (2004) mandatory shifts relating to gear (e.g. hooktypes)
and baits, the ramifications of which are only beginning to be
investigated in relation to shark interactions. An insufficient period
of time has elapsed for complete industry acclimation to these new
protocols and for any discernable shifts in catch-per-unit-effort
(CPUE) to be reliably linked to this phase-shift.
Shark bycatch in the Atlantic PLL must be addressed for the sakes of
both sustaining shark populations and the best interests of industry.
Despite the aforementioned caveats associated with data collection,
there is a plethora of work that has addressed shark bycatch in the
Atlantic PLL fishery through which trends and conclusions can be
established and new questions/objectives can emerge. We intend to
consolidate the various works while highlighting key findings from
the diverse array of available studies and unpublished analyses. Upon
gauging the extent in which sharks interactions have been problematic
in the Atlantic PLL fishery, subsequent mitigation strategies with
global implications can be investigated.
A9.1.2. Geographic fishing zones and status of the fleet
The U.S. Atlantic, Caribbean and Gulf of Mexico PLL fishery is
typically analyzed and managed according to 11 distinct zones
spanning from the Gulf of Mexico (GOM) to the West, Northeast
Distant (NED) to the North, to Tuna South (TUS) at the southern
terminus (Fig A9.3) (NMFS, 2005). Within this geographic domain,
there have conventionally been five sub-fisheries composing the
overall domestic operation: the Caribbean Island Tuna and Swordfish
fishery; the Gulf of Mexico Yellowfin Tuna fishery; the South Atlantic
Florida East Coast to Cape Hatteras Swordfish fishery; the Mid-
Atlantic Swordfish and Bigeye Tuna fishery; and the U.S. Atlantic
Distant Water Swordfish fishery. A smaller-scale PLL operation also
targets wahoo and dolphin in the Atlantic. These fishery “segments”,
which are comprehensively described in the consolidated Highly
Migratory Species Fishery Management Plan (HMS FMP) (NMFS,
2005), are diverse in their fishing regimes, gear-types, ranges and
degree of transience, vessel numbers and sizes, and whether seasonal
or perennial in operative nature.
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