Background
Harbour porpoises (Phocoena phocoena) in eastern Canada are listed as threatened by Committee
on the Status of Endangered Wildlife in Canada because of the large
incidental catches of these animals in commercial fisheries (Gaskin 1992).
The most recent DFO and NMFS estimates suggest that as many as 4.3 % of the
Bay of Fundy and Gulf of Maine population are killed each year in gill nets
(Trippel et al. 1996). To date no recovery plan has been formulated for
harbour porpoises in eastern Canada. Our satellite telemetry research will
assist in the conservation of harbour porpoises in both Canada and the
United States.
The satellite telemetry study continues to provide information that can be
used directly in the formulation of an effective conservation strategy for
this population. The movements of harbour porpoises from areas of gillnet
fishing effort in the Bay of Fundy to similar fishing grounds in the Gulf
of Maine indicate that individuals in this population are at risk of
entanglement during several periods of the year. For example, by referring
to the map from Bjorn it is evident that this porpoise travelled from the
most concentrated area of Canadian gillnet fishing effort in August to an
area of intense US gillnet activity, located just north of Cape Cod. These
movements emphasize the trans-boundary nature of the Bay of Fundy/Gulf of
Maine population and the need for coordinated management between Canada and
the United States in resolving conflicts between porpoises and gillnet
fisheries. These data also allow us to evaluate, albeit in preliminary
fashion, the efficacy of time-area fishery closures as a management
strategy for reducing the level of incidental mortality. Our data indicate
that porpoises exhibit a high degree of individual variability in their
movements (compare the movements of Otis and Bjorn), suggesting that
effective closures will have to be extensive in time and space. The
fishing industry has proposed the use of trigger mechanisms, so that
fishery closures would be tied to the appearance of harbour porpoises in
particular areas, thus minimizing disruptions to fishing activity. Our
results suggest that the movement patterns of individual harbour porpoises
are extremely variable and are not currently predictable on a scale that
would serve as a useful trigger mechanism.
The methods used follow those developed by our team over the past three
years. The movements of harbour porpoises are studied by attaching small
satellite transmitters (PTTs) to animals that are released from herring
weirs (see below) along the south-western coast of New Brunswick between
mid-July and late-September. These packages are approximately 11 x 4 x 1.5
cm and have a mass in air of 200 g. Transmitters are attached to the
dorsal fin using three delrin pins. These same transmitters were used
on porpoises in 1995 giving reliable daily positions for up to 212 days.
We use model ST-10 PTTs, manufactured by Telonics (Mesa, Arizona). The
PTTs incorporate a salt water switch so that they only transmit when the
antenna breaks the surface (this prolongs battery life by eliminating
underwater transmissions). The transmitters are powered by two 2/3 A
cells, which should provide several months of battery life. The PTTs are
programmed to transmit eight hours each day, to meet the Standard
Scientific Service Classification of System ARGOS; this programmed duty
cycle is fine-tuned to maximise the overlap between transmitting periods
and satellite overpasses. Data are downloaded from the NOAA weather
satellites to the ARGOS Global Processing Centre in Landover, MD and then
accessed via the internet. We are able to collect more or less continuous
distribution and movement data from tagged porpoises during the course of
the PTT deployments.
The Harbour Porpoise Release Program
The harbour porpoise release program continues to provide immediate
conservation action by saving animals that might otherwise drown in herring
weirs. The weir release program remains the priority at the Grand Manan
Whale and seabird Research Station and the backbone of our other
conservation based research activities.
The harbour porpoise release program was developed by the Grand Manan Whale
and Seabird Research Station in 1991 in order to assist weir fishers in the
Bay of Fundy with the safe release of harbour porpoises from their herring
weirs. Porpoises become trapped in these structures while following
schools of herring along the shore line. While trapped in a weir porpoises
are able to swim, breathe and feed, but do not seem able to swim out.
Through the release program, porpoises can be removed safely from weirs
when the herring are harvested. This process requires the participation of
both fishers and members of our research team.
The summer of 1997 marked the seventh year the release program has been in
full-scale operation on Grand Manan Island. Since its inception in 1991
the program has grown and we now receive participation from most local weir
fishers. The program runs between mid-July and mid-September when the
highest densities of porpoises are found near-shore and entrapments are
most likely to occur. The number of releases typically varies between 40
and 100 per summer. We will follow the same protocol as we have used in
previous years. Each morning all the weirs in the northern region of Grand
Manan are checked by station personnel using one of our small boats.
Owners of weirs with trapped porpoises are then alerted and a seining is
scheduled, usually within two days. Weir fishers also check their weirs
daily and many will contact us directly to inform us when the next seining
is going to occur. Porpoises are seined out with the herring using the
fisher's fine mesh seine net or independently using our own marine mammal
seine. This lightweight net was specially constructed to make seinings
safer for trapped porpoises. Its large mesh size allows herring to swim
through the net, improving visibility and reducing the chances that a
tangled porpoise would go unnoticed and drown.
Contact emails:
Andy Read
aread@mail.duke.edu
Andrew Westgate
westgate@acpub.duke .edu
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