The Net Effect? - Whale and Dolphin Conservation Society

y the (full-time) Galician fleet is estimated to
be around 1.1 million per year (López et al.
2003). These findings also appear to be at
odds with other recent surveys. For instance,
a survey of cetacean bycatch in Galician fisheries
conducted in 1998-1999 recorded no
bycatch during 67 observed fishing trips
(López et al. 2003). However, data from interviews
with fishermen produced an estimated
annual cetacean bycatch of 415 cetaceans per
year in Galician offshore trawl fisheries and a
further 332 in the trawl fishery on Grand
Sole. The interviews also yielded numerous
references to cetaceans being used for human
consumption (69 out of 500 interviewees) and
use of cetaceans for bait, animal food and as a
source of fat was also mentioned (López et al.
2003). An earlier Spanish study, also using
observers and interviews with fishermen, identified
offshore pair trawling as the major cause
of common dolphin mortality (Aguilar 1997).
In this study, fishermen reported that during
night-time fishing it was rare not to catch
dolphins, usually between one and ten and
sometimes thirty or more. During 1996 and
1997, observers were present on four trips
using pair trawls at night and in all cases
common dolphins were caught, totalling eight
individuals (Aguilar 1997).
3.3 Bottom-set gillnets
Gillnetting is a simple, passive form of
fishing that involves the setting of sheets of
netting suspended vertically in the water by
way of a floatline at the top and a leadline at
the bottom. Fish are caught by swimming
into the net and becoming wedged within a
mesh opening, or literally ‘gilled’ by the mesh
catching behind the gill covers. Bottom-set
gillnets are used to catch a wide variety of
demersal species including cod, turbot, hake,
saithe and dogfish. There are several variations
on this theme. Tangle nets have little or
no flotation so that they are extremely slack,
and are used to catch species such as flatfish
and crustaceans, which are entangled rather
than gilled. Trammel nets consist of three
parallel sheets of netting, the middle sheet of
which has a smaller mesh and is hung
loosely, so that fish swim through the outer
sheet and are caught in a pocket of the small
mesh netting. All these nets are usually
anchored so that they are located on or near
the seabed. Driftnets are gillnets that are left
to drift at or near the sea surface, sometimes
attached to the boat at one end (driftnets are
addressed in 3.4 below).
Although gillnets have a long history, their
use has increased massively since the introduction
in the 1950s of nylon yarns and particularly
monofilament netting, which
increased their efficiency (Northridge et al.
1991). The FAO and other organisations
actively promoted the use of gillnets in
coastal areas because of their low cost, ease
of use and productivity, and they have
became the most common type of fishing
gear in coastal waters worldwide (Crespo &
Hall 2001). Gillnets are regarded by fisheries
managers as attractive because they can be
very size-selective for the target fish.
However, they can be very unselective at a
species level, both for non-target fish and for
other groups such as marine mammals, birds
and turtles. The durability of nylon gillnets
also means that when they are lost at sea
(which frequently happens) they may
continue to trap fish (ghost fishing) for an
indeterminable period, posing an additional
bycatch threat.
The harbour porpoise, in particular, has been
found to be acutely prone to incidental
capture in bottom-set gillnets in the northeast
Atlantic and many other regions
throughout its range (see also 2.2.2).
3.3.1 Danish bottom-set gillnets
Denmark has a large bottom-set gillnetting
fleet, operating largely in the North Sea and
also in the Kattegat and Skaggerak Seas and
into the Baltic Sea. The main fisheries
targeted in the North Sea are for cod, caught
in bottom-set nets and wreck nets (where
gillnets are set over wrecks and rough
The Net Effect?
A WDCS report for Greenpeace
33