Shark Depredation and Unwanted Bycatch in Pelagic Longline

Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries
A2.4. Range of Fishing Gear and Methods
Fig. A2.1. Bycatch species in the Chilean industrial longline swordfish
fishery, 2005 (Barría et al., 2006).
fishing areas are in front of Valparaiso and Concepcion at 80°W
(Barria et al., 2006). The fishery has been monitored by IFOP since
2001 through the collection of information from shore based and
onboard observers. During 2005 the onboard observer program
covered 74% of the industrial vessels (Barria et al., 2006).
A2.3. The Elasmobranch Fishery
The Chondrichthyans fishery has become an important resource for
developing countries. Its role increased in terms of food and income
generation due to the increasing demand for shark fins, the increase
in human population, and the decline in landings of traditional
species. Developing countries’ catches increased from 76,000 metric
tons (MT) in 1950 to 575,031 MT in 2000 for a value in the year 2000
of $515 million (Cattarci, 2004; FAO, 2006) .
Chile has a fishery targeting chondrichthyans. This fishery has
increased significantly over the last few decades. Table A2.1 and
Fig. A2.2 show the production of elasmobranchs in Chile for the past
several decades.
The species of chondrichthyans captured for commercial ends in
Chile include primarily makos (Isurus oxyrhinchus), blues (Prionace
glauca), smoothhounds (Mustelus sp.), yellownose skates (Dipturus
chilensis), D. trachyderma, and a holocephali (chimera) known as
“pejegallo” (Callorynchus callrynchus) (Sernapesca, 2006). Fig. A2.3
shows the catches of these species of chondrichthyans in Chile from
1990 to 2005 (SERNAPESCA, 2006).
For this study we conducted interviews of artisanal longliners
in Chile’s northern regions. These vessels target mahi mahi and
sharks primarily during the summer months. We also surveyed the
industrial swordfish longline fishery where sharks are captured as
bycatch.
A2.4.1. Artisanal mahi mahi longline
This fishery operates in Arica, Iquique, Tocopilla, Antofagasta and
Caldera (Barria et al., 2006). Vessels are between 9.1 and 13 meters
total length (Barria et al., 2006). They typically work with a surface
horizontal longline. Mainline length varies slightly by boat from
2,700 to 3,600 meters. Number of hooks also varies but is typically
about 100-350. Mahi mahi season is from December to March. Trip
length varies by season with mahi mahi trips typically lasting 3 to
4 days. Almost all vessels use J hooks. Bait species include sardine,
mackerel and flying fish (Barria et al., 2006). Total boat crew generally
consists of 2 to 3 persons. Gear is set around 7:00 AM and hauled at
4:00 or 5:00 PM (Barria et al. 2006 and present surveys). Weighted
swivels and steel leaders are used during the shark season. Table A2.2
provides a comparison of artisanal mahi mahi gear with industrial
longline swordfish gear.
A2.4.2. Industrial swordfish fishery
This fishery mainly uses the American longline configuration (12 of
16 vessels) but several vessels use the Spanish configuration. The following
information on gear characterization for both configurations
was taken from Barria et al. (2006). See Table A2.2 and Figs. A2.4
and A2.5 for a comparison of longline gear configurations.
The Spanish configuration includes a mainline of braided polypropylene
rope. The mainline is divided into 110 hooks sections. Each
of these sections has a radio beacon buoy at its beginning and end.
Every 23 fathoms there is a branchline with a hook, and each branchline
is knotted to the mainline. A buoy is placed every 10 branchlines.
Branchlines are 4.5 fathoms long. Leaders are made of polypropylene
but also has a portion made of metal cable (1.5 mm diameter).
This cable adds weight to the line and is better able to retain sharks.
Vessels usually deploy a 45 nautical mile long mainline containing
approximately 2,000 hooks. The Spanish system does not allow for
variation in the depth of the hooks. These vessels also use photoactive
plastic polymer balls that glow after being exposed to light. Each
hook has four of these. Spanish and Chilean mackerel and squid (Ilex
argentinus) are used for bait.
The American configuration has a monofilament mainline. In this
system the mainline is divided into sections of 220-250 hooks with
a radio beacon buoy at the beginning and end. The mainline usually
has a total of 7 beacon buoys and 1500 (range of 1200-2000) hooks.
Distance between hooks and depth of hooks can be modified. Every 5
hooks there is a float buoy. As the distance between hooks is increased,
the maximum depth of the hooks increases as does the total mainline
length. Mainline length ranges from 35 to 55 nautical miles.
The American configuration uses lights in the weighted swivel
(65-75g.). These may be chemical or battery powered. Light are
green or violet. Branchlines may be 6 to 18 meters long and have a
15-20 cm cable leader. This system uses a timer for setting of hooks
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All prices are given in U.S. dollars unless otherwise indicated
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