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Duke University Marine Lab
Harbor Porpoise
Program
Harbor Porpoise


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.


Duke University Marine Lab
135 Duke Marine Lab Road
Beaufort, NC 28516
Ph 919-504-7589
Ph 919-504-7589

Contact emails:
Andy Read
aread@mail.duke.edu

Andrew Westgate
westgate@acpub.duke .edu


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