The Net Effect? - Whale and Dolphin Conservation Society

(1.5%) and white-beaked dolphin (1.5%)
(Couperus 1997a).
Further monitoring of the Dutch mackerel
and horse mackerel fishery in the Celtic Sea
and south-west of Ireland was conducted in
January to March of 1994 and 1995. This
sampled 119 tows over 841 hours of towing,
representing 3% of annual effort (Morizur et
al. 1999). The observers recorded catches of
nine dolphins, consisting of five Atlantic
white-sided and four common dolphins. This
represents a bycatch rate of 0.076 animals
per tow, or 0.01 animals per hour of towing.
The animals were all caught at or near the
continental shelf edge and the bycatches
occurred either at night or in the early
morning even though more hauling operations
were actually conducted during
daylight (Couperus 1996).
The body temperature of the bycaught
animals was measured and ranged from
26.6ºC to 38ºC, and exceeded 34ºC for seven
of the individuals, which is close to that for a
living animal (37ºC). This finding, along with
the state of rigor mortis, was taken to indicate
that the animals had only recently died and
had been captured during or close to hauling,
perhaps being trapped by net closure during
the haul-back process. It was also noted that
when a vessel turns sharply during a tow, the
fishing line is hauled in until the trawl doors
break the surface and the net itself is closed
just under the water surface (known as
‘turning on the doors’). After turning, the line
is paid out again, the whole process lasting for
10-20 minutes in water depths of 200 m. This
procedure was also considered likely to
increase dolphin bycatches compared to
a haul maintained in the same direction
(Couperus 1996).
In five out of the six bycatch incidents the
bulk of the fish catch was mackerel
(Couperus 1996). Analysis of bycaught
dolphins’ stomach contents has shown that
white-sided dolphins were feeding heavily on
mackerel shortly before capture, but not on
horse-mackerel, even when the latter was
present in the catches (Morizur et al. 1999).
Trawling depth for mackerel in this fishery
was reported to be between 100 m and 400
m and the duration of hauls in which
dolphins were caught ranged from 4.5 hours
to over 12 hours (Couperus 1996).
Bycatch monitoring continued in the Dutch
fishery in 1995-96, when 84 hauls were
sampled over 45 days at sea, and eight
cetaceans were recorded as bycaught.
During the course of the study, an additional
37 animals were recorded as bycaught in
skippers’ reports. However, there were insufficient
data to estimate annual bycatch rates
(Couperus 1997b).
No further bycatch monitoring has been conducted
in the Dutch pelagic trawl fisheries.
However, Dutch fishing intensity south-west
of Ireland is assumed to have reduced as
part of the fleet has moved to Moroccan
and Mauritanian waters. The African fishing
grounds are of growing importance and
accounted for more than 35% of the total
earnings of the fleet in 2001 (Anon. 2003).
Dolphin bycatch is also reported to be high
in the Mauritanian fishery (CEC 2002b).
3.2.3 UK pelagic trawl fisheries
The UK pelagic trawl fleet targets a range of
fisheries including mackerel, herring, sprat,
pilchard, blue whiting, anchovy and sea bass,
and operates in waters all around the British
Isles including the northern waters of ICES
area II and south into the Bay of Biscay. The
number of vessels in the UK’s pelagic fleet
was 67 in 1995, decreasing to 47 in 2001.
However, the installed engine power of the
fleet increased by 30%, from 82,900 hp to
108,150 hp, over that period (Anon 2003).
The total landings of the UK pelagic fleet
were 324,000 tonnes in 2001. Mackerel is
the most important species, accounting for
around 50% of landings, followed by
herring, at around 35%. The other species
The Net Effect?
A WDCS report for Greenpeace
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