The Net Effect? - Whale and Dolphin Conservation Society

18
The Net Effect?
A WDCS report for Greenpeace
area extending south-west of Ireland to
France and north-west Spain (excluding the
Bay of Biscay) and westwards to 20º W
(Goujon et al. 1993).
Striped dolphins in the north-east Atlantic
feed on a variety of small pelagic and benthic
fish, including sprat, blue whiting, silvery
pout, hake, horse mackerel, bogue, anchovy
and gobies. Squid and crustaceans are also
frequently taken (e.g. Desportes 1985; Santos
Vázquez 1998). Surveys in the western
Mediterranean indicate the striped dolphins
may feed along the shelf edge at night and
move offshore during the day (Gannier &
David 1997).
2.4.2 Bycatch of striped dolphins
Striped dolphins do not appear to be attracted
to vessels to the same extent as common
dolphins (Reid et al. 2003). However, there is
evidence of their entanglement in a number
of fishing operations.
In the 1990s several studies were made of
bycatch in the driftnet fishery for albacore
tuna in the north-east Atlantic which occurs
in the summer months (see also 2.3.2
above). Substantial catches of striped
dolphins were recorded in the French
driftnet fleet in 1992 and 1993. This fleet
operated in north-east Atlantic waters
within and beyond the Bay of Biscay using
driftnets nominally 5 km long, producing an
estimated bycatch by the whole fleet of
almost 1200 striped dolphins a year (of a
total of 1,700 cetaceans taken) (Goujon et
al. 1993). This bycatch rate was deemed to
be unsustainable (Woodley 1993; CEC
1993). Use of a demographic model for
striped dolphins indicated that the population
can only sustain incidental mortalities
of up to about 1% per year (Woodley
1993). This compares with estimated mortality
rates of 1.62% and 1.56% of the population
for the years 1992 and 1993 respectively
in the French driftnet fishery alone
(Goujon et al. 1993)
Observation of the UK’s much smaller
albacore driftnet fishery (using 2.5 km long
nets) in 1995 resulted in an estimate of total
bycatch for the UK fleet of 165 dolphins, of
which 104 were striped dolphins and the rest
common dolphins (SMRU 1995). Subsequent
results from observations of the Irish
albacore driftnet fishery demonstrated an
even higher cetacean bycatch rate, and
produced an estimated total bycatch of 535
cetaceans (including 134 striped dolphins) in
the fishery in 1996 (Harwood et al. 1999).
The extrapolated bycatch figure for 1998,
when the number of vessels in the Irish
fishery had increased, was 3,754 (including
964 striped dolphins). Largely as a result of
the cetacean bycatch, the decision was made
in 1998 to prohibit of the use of driftnets in
the albacore and similar fisheries, a prohibition
which came into force in January 2002
(see also 3.4.1).
Bycatch of striped dolphins has also been
recorded in the Irish pelagic pair trawl
fishery for albacore tuna, which ironically
was introduced to replace the prohibited
driftnet fishery (see also 2.3.2 above). This
fishery also occurs in the summer months.
A study of the trial fishery in 1999 monitored
a total of 313 hauls over 160 days by
four pairs of trawlers and recorded a bycatch
of 145 cetaceans, eight of which were striped
dolphins (the majority being common
dolphins) (BIM 2000).
2.5 Atlantic white-sided dolphin
(Lagenorhynchus acutus)
2.5.1 Ecology, population
and distribution
Atlantic white-sided dolphins are very gregarious
animals and frequently mix with other
cetacean species, particularly white-beaked
dolphins, and sometimes bottlenose and
common dolphins and larger whale species.
The species sometimes gathers in very large
groups of up to 1,000 individuals, within
which smaller subgroups of some 2-15 animals
can often be distinguished (Reid et al. 2003).