Shark Depredation and Unwanted Bycatch in Pelagic Longline

Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries
A7.4. Fishing Gear and Operations
There are two distinct pelagic or surface longline gear configurations
used in South African waters based on whether the target species is
swordfish or tuna. To target swordfish the hooks are generally set
shallow (seldom deeper than 40 m) by using short buoylines and
branchlines and no line setter. In general lightsticks are also used.
This gear configuration generally characterizes the South African
domestic fleet. Those that target tuna set the hooks deep (often
deeper than 200 m) by using a line setter and long buoylines and
branchlines. Lightsticks are seldom used. This gear configuration is
generally employed by the Japanese and Taiwanese fleets.
Fig. A7.1. Fishing effort by foreign vessels (Japanese and Taiwanese)
operating in South African pelagic longline fishery (1996-2002) under
bilateral agreement.
Fig. A7.2. Fishing effort by domestic vessels operating in South African
pelagic longline fishery (2000-2005).
Fig. A7.3. Fishing effort by foreign vessels operating under joint-venture
agreements in South African pelagic longline fishery (2004-2005).
There were on average 17 (range 1-26) vessels in the domestic fleet
between 1997-2003. Thirty vessels carried an observer at least during
this time period. This description of the fishery is derived from this
subset of the fleet (n=615 sets on 70 trips) as well as information
provided in interviews. Sampled vessels vary in size (average 31 m,
range 19-56 m, std dev 7.9 m) and carry an average of 18 (range 6-31,
std dev 5) crew members. Trips (n=70) are on average 14 (range 5-38,
std dev 5.8) days.
In general a mainline, which could be over 50 miles, is usually made
of monofilament nylon. It is usually set between late afternoon
and midnight (43% set in the dark, 2% in the light and 55% during
twilight) and is allowed to soak until dawn (note: dark/light = start
to finish in the dark/light, twilight = start in the dark or light and
end in the other). The line is kept close to the surface by numerous
buoys which are attached to the mainline via buoylines at an average
of 194 m (range 46-370 m, std dev 108) apart and are on average 20
m (range 10-37 m, std dev 3 m) long. Additional radio or light buoys
are also used to locate the line. There are between 20 and 472 (average
272, std dev 100) buoys on a line and on average five (range 3-30, std
dev 3) branchlines or snoods between buoys. On average 1300 (range
1000-2500) hooks are attached to the mainline the branchlines.
Branchlines are spaced evenly along the mainline at an average of
42 m (range 17-65 m, std dev 15) apart. A typical South African
flagged pelagic longliner makes up their branchline to the following
specifications (Table A7.1): an upper section of approximately 18 m,
a swivel (usually 60-80g) and a lightstick and then a lower section of
approximately 2 m ending in a baited hook.
Eighty nine percent of observed vessels used squid as bait, with the
remaining 11% using a combination of squid and between 8-75% fish
bait (pilchard, mackerel). This is consistent with interview results.
None was recorded using live bait. According to observer data 23% of
vessels did not use light sticks (most likely those targeting tuna), 5%
used light sticks on less than 50% of their branchlines, 3% used light
sticks on 50% of their branchlines, 12% used light sticks on between
51-99% of their branchlines and 57% used light sticks on 100% of
their branchlines. All those interviewed said they always use light
sticks. 10% of observed vessels used a line setter. In general the line is
set at an average speed of 8 knots.
114