Subject: Abstracts: NE Atlantic bycatch and pollution - recent publications (fwd)

Mike Williamson (
Fri, 25 Jun 1999 07:39:38 -0400 (EDT)

---------- Forwarded message ----------
Date: Thu, 24 Jun 1999 14:05:56 +0100
From: Simon Berrow <>
Reply-To: Marine Mammals Research and Conservation Discussion
Subject: Abstracts: NE Atlantic bycatch and pollution - recent publications

Recent publications on bycatch and pollution studies of marine mammals in
the NE Atlantic.

Morizur,Y., Berrow, S.D., Tregenza, N.J.C., Couperus, A.S., & Pouvreau,
(1999) Incidental catches of marine mammals in pelagic trawl fisheries of
the Northeast Atlantic.  Fisheries Research 41, 297-307.

Marine mammal by-catch in eleven pelagic trawl fisheries operated by four
different countries in the Northeast Atlantic were studied.  Observers
accompanied commercial fishing vessels and monitored 374 tows totalling
1771 hours of towing during 377 days fishing.  Three species of marine
mammal were definitely by-caught (white-sided dolphin Lagenorhynchus
acutus, common dolphin Delphinus delphis and grey seal Halichoerus grypus)
and probably also a bottlenose dolphin Tursiops truncatus.  Dolphins were
caught in four of the eleven fisheries and seals in one.  In those
fisheries with cetacean by-catch, rates varied from 0.0606 to 0.1000 per
tow and 0.0107 to 0.0137 per hour of towing and were highest in the French
sea bass fishery and lowest in the French tuna fishery.  Grey seals were
caught in the Irish Celtic Sea herring fishery at a rate of 0.0513 per tow
or 0.0396 per hour of towing. The mean q SD dolphin catch rate for all
fisheries combined was 0.048q0.013 per tow (1 dolphin per 20.7 tows), or
0.0185q0.0019 per hour of towing (1 dolphin per 98 hours of towing) and,
for all marine mammals, 0.059q0.019 (1 per 17.0 tows) or 0.0124q0.0121 (1
per 80.6 hours of towing). 95% confidence intervals, calculated on
untransformed data, for all fisheries combined were 0.4-1.6 dolphins per
100 hours of towing.
        No operational factors were correlated with by-catch rates but the
haul-back procedure was identified as a potentially important factor.  All
dolphin by-catches occurred during the night which may be a due to an
association between cetaceans and trawlers at night.  White-sided dolphins
and grey seals were observed feeding around the net during towing and this
behaviour is suggested as making them more vulnerable to capture.
Operational difficulties in observing by-catch and potentially significant
annual fluctuations in catch rates warrant further observer studies of
these and other trawl fisheries.

Berrow, S.D. & Rogan, E. (1998) Incidental capture of cetaceans in Irish
waters.  Irish Naturalists' Journal 26 (1/2), 22-31.

No abstract

Berrow, S.D., Long, S.C., McGarry, A.J., Pollard, D., Rogan, E. &
C. (1998) Radionuclides (Cs-137 and K-40) in Harbour porpoises Phocoena
phocoena L. from British and Irish waters.  Marine Pollution Bulletin
36(8), 569-576.

Mean concentrations of 137Cs and 40K in harbour porpoises are presented.
Concentrations of 137C in porpoises originating from the Irish Sea were
elevated relative to those from the Celtic Sea, Atlantic seaboard and the
North Sea.  Concentrations of 40K were comparable between samples from all
locations and similar to those reported elsewhere.  Concentration factors
(CF) determined for Irish Sea porpoise did not differ significantly from
those measured for other regions.  The dose arising from 137Cs and 40K was
dominated by the internal component.  As most of the total dose was
attributable to the naturally occurring 40K it is unlikely that the
increased dose due to the anthropogenic input of radionuclides has a
detrimental effect on health of the Irish Sea porpoise.  Elevated
concentrations of 137Cs in porpoises from the Irish ea suggest they may be
resident in the area.

Berrow, S.D., O'Neill, M. & Brogan, D. (1998) Discarding practices and
marine mammal bycatch and in the Celtic Sea Herring Fishery.  Biology and
Environment.  Proceedings of the Royal Irish Academy (1)1-8.

Pelagic fisheries account for 83% of the total number of fish landed into
Irish ports, with mackerel Scomber scrombrus , horse-mackerel Trachurus
trachurus and herring Clupea harengus constituting 97% of this.  Despite
the importance of pelagic fish species there is little published
information on discarding practices for most Irish trawl fisheries and no
study of marine mammal bycatch.  Fisheries scientists accompanied
commercial trawlers fishing herring in the Celtic Sea during the 1995/95
season.  During the study 85 days were spent at sea, with 78 tows
monitored, accounting for 101 hr of fishing effort, which was 75 of the
total effort in the fishery.  Most fishing was carried out in ICES
divisions VIIg01, VIIg02 and VIIa20, and most fish caught in VIIg01 and
VIIa20. The fishery was very selective, with 99.5% of the total weight of
the catch being the target species.  Mean size (qSE) of herring caught was
extremely consistent, ranging from 24.8q2.7 cm in October to 26.0q2.0 cm in
January.  Overall, 1270 tonnes offish were observed being caught, of which
1214 tonnes were landed and 57 tonnes discarded (4.7%).  Whiting Merlangius
merlangus was the most frequently recorded non-target fish species;
mackerel and horse-mackerel were also frequently caught.  Four grey seal
Halichoeus grypus were caught during the study at a rate of one seal per
317.5 tonnes of fish or 0.05c seals per tow. This catch rate extrapolates
to around 60 seals caught in the fishery, which is not enough to have a
significant impact on the Irish seal population.

Dr Simon Berrow,
Marine Life Sciences Division,
British Antarctic Survey,
High Cross, Madingley Road,
Cambridge, CB3 OET, UK

Tel: 01223 221611
Fax: 01223 221259