Subject: Bycatch and midwater trawl (fwd)

Mike Williamson (pita@www1.wheelock.edu)
Thu, 7 May 1998 14:33:53 -0400 (EDT)

---------- Forwarded message ----------
Date: Thu, 7 May 1998 08:21:33 -0100
From: Bram Couperus <bram@rivo.dlo.nl>
Reply-To: Marine Mammals Research and Conservation Discussion
     <MARMAM@UVVM.UVIC.CA>
To: MARMAM@UVVM.UVIC.CA
Subject: paper on bycatch and midwater trawl



Couperus, A.S. 1997. Interactions between Dutch midwater trawl and Atlantic
white-sided dolphins (_Lagenorhynchus acutus_) southwest of Ireland.
_Journal of Northwest Atlantic Fishery Science_ 22:  pp. 209-218.


Mailing adress:
Netherlands Institute for Fisheries Research (RIVO-DLO), P.O. Box 68, 1970
AB, IJmuiden, The Netherlands


Abstract

Incidental by-catches of cetaceans in the Dutch pelagic trawl fishery are
largely restricted to late-winter early spring in an area along the
continental slope southwest of Ireland. Available evidence indicates that
annual variations in such incidents are large. Using combined midwater
trawl bycatch and dolphin stomach content data, the hypothesis is put
forward that Atlantic white-sided dolphin (_Lagenorhynchus acutus_),
normally a more oceanic species, may actively search for mackerel (_Scomber
scombrus_) closer to shore in early-spring, at least in some years.
Supporting data were from an observer program during 1992-1994, which
covered seven trips representing 5% of the annual effort in  the fishery.
Also over the period 1989-1994, a total of 71 records of bycatch incidents
were collected (involving a minimum of 312 individuals), of which 41
occured in 1994 (172 individuals). Approximately 90% of the incidents
occurred late-winter early spring, when both the mackerel and horse
mackerel (_Trachurus trachurus_) pelagic fisheries were operating in the
same area, southwest of Ireland. Incidence frequency peaked by late
February and in March, when mackerel is known to move into the area during
its southward migration. The Atlantic white-sided dolphin  was the main
cetacean species in the bycatch (83% of all identified individuals). Other
species recorded included long-finned pilot whale (_Globicephala melas_),
short-beaked common dolphin _(Delphinus delphis_), bottlenose dolphin
(_Tursiops truncatus_) and the white-beaked dolphin (_Lagenorhynchus
albirostris_). The stomachs of 47 Atlantic white-sided dolphins, 11 common
dolphins, two bottlenose dolphins and one white-beaked dolphin were
examined. Fresh mackerel remains were found in nearly all white-sided
dolphins stomachs, whereas fresh horse mackerel remains occured only in
stomachs of bottlenose and common dolphins. Deep-water fish otolith
incidents suggested that white-sided, common, and bottlenose dolphin had a
completely different diets before moving to the southwest of Ireland.

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A.S. Couperus
Netherlands Institute for Fisheries Research (RIVO-DLO)
P.O. Box 68
1970 AB  IJmuiden
The Netherlands
phone: (+31)255.564690
fax: (+31)255.564644
E-mail: bram@rivo.dlo.nl

Notes:
- usual name: Bram
- In Dutch the first two characters in "IJmuiden" are to be considered as
one character and should therefore both be written in uppercase.
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