The Net Effect? - Whale and Dolphin Conservation Society

24
The Net Effect?
A WDCS report for Greenpeace
In addition, in most European waters,
logbook recording requirements only apply
to boats over 10 m, and at present data collection
requirements do not include those for
assessing environmental impacts.
Based on experience from existing and
previous observer monitoring schemes,
advisers to the European Commission have
recommended that an initial sampling level
of 5-10% of the total, annual fleet effort is
necessary in most fisheries to determine the
approximate level of bycatch (CEC 2002b).
Higher levels than this are recommended in
areas where there are known problems of
cetacean bycatch. In particular, observer
coverage in the pelagic trawl fisheries in the
Biscay, Celtic Sea and Channel area is recommended
to be “as high as feasible” during
December to March when mass strandings
of bycaught dolphins occur (CEC 2002b).
Clearly, the more observation is conducted,
the more precise the estimate of total bycatch
will be (as long as there are adequate data on
the fishing effort).
Where observation schemes are not in place,
records of stranded animals, where they have
been subject to post-mortem examination,
can be used to identify the existence of a
bycatch problem in an area. However,
strandings data cannot provide any more
than an absolute minimum level of bycatch,
as the rate at which bycaught and discarded
animals are washed ashore is highly variable
and unpredictable (CEC 2002a).
Details of injuries of stranded bycaught
animals can, though, provide an indication
of the type of fishery responsible, for
instance whether large-mesh monofilament
net or small-mesh trawl-type netting was
involved (Sabin et al. 2003). In addition,
analyses of stomach contents of bycaught
animals may show which fish the cetaceans
were feeding on when or immediately before
they were caught, which may again give an
indication of the fishery responsible (e.g.
Kuiken et al. 1994). Details of carcasses
that are retrieved by onboard observers, such
as body temperature, can also provide useful
information as to how and when the animals
were killed (e.g. Morizur et al. 1999).
The following section describes in some
detail the main pelagic trawl fisheries, and
outlines other key fishing types, where data
are available, that are known or suspected
to be associated with cetacean bycatch in the
north-east Atlantic.
Much of the information presented is the
result of extremely limited observer programmes.
Until comprehensive observer data
is available and analysed, the true extent of
the cetacean bycatch problem will not be
apparent. However, from the limited data
available in the following sections, there is
clear cause for concern.
3.2 Pelagic trawls
Pelagic or mid-water trawling involves the
towing of a trawl net, which is essentially a
bag net with a very wide mouth that gradually
tapers to a narrow tube known as the
extension piece, leading in turn to the closed
end of the net, the cod-end, where the fish
are collected. Pelagic trawl nets typically
have large floats on the head line at the
mouth of the net to keep the mouth open,
and weights on the footrope at the sides, or
wingends, of the net opening. The net
consists of very large mesh size at the mouth,
gradually decreasing along the net to a small
mesh at the cod-end, depending on the size
of fish being targeted. A pelagic trawl net can
be towed either by a single boat (single
trawl) or by a pair of boats (pair trawl), with
the configuration of the gear varying between
these two fishing methods, as well as
between different fleets.
Mid-water trawls are considered to have a
much greater potential to capture cetaceans