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Information on Species Designated by COSEWIC: Harbour Porpoise
The rest of this workbook is structured to provide you with specific information on the Harbour Porpoise (Northwest Atlantic Population). Information is provided on COSEWIC status, distribution and biology, reason for designation by COSEWIC, potential management measures and impacts. For the full Harbour Porpoise status report that includes the threats and limiting factors please visit: http://www.sararegistry.gc.ca.
What is the Harbour Porpoise?
The Harbour Porpoise (Phocoena phocoena) is a small marine mammal related to whales and dolphins. It rarely reaches a length greater than 1.7 meters, with females slightly larger than males. As the name suggests Harbour Porpoise are often seen in bays (especially in summer), although they have also been seen hundreds of kilometers offshore. Breeding takes place in early summer and 10 – 11 months later a single calf is born and nursed for at least 8 months. Females commonly reach sexual maturity between the ages of 3 and 4 years while males mature slightly earlier. The oldest recorded age for a Harbour Porpoise is 24 years but most do not live past their teens.
As a small marine mammal with limited energy reserves Harbour Porpoise are frequent feeders and their distribution at any given time is associated with the distribution of prey. They eat mainly small fish and cephalopods less than 30 cm in length. They are attracted to prey-rich areas, especially of fat-rich prey such as capelin and herring.
Where is the Harbour Porpoise found?
Harbour Porpoise live in the temperate waters of the northern hemisphere. They are widely distributed on the continental shelves of the northern oceans with several separate and distinct populations. The Atlantic and Pacific populations of Canadian Harbour Porpoise are separate subspecies. Within the Atlantic Ocean Harbour Porpoise in the northeast Atlantic are effectively separated from those living in the northwest Atlantic. Recently, populations in the English Channel and the Baltic Sea have disappeared.
In eastern Canada Harbour Porpoise are found from the Bay of Fundy to Baffin Island. DNA and toxicology evidence suggests that there are three discrete populations summering in eastern Canada (Newfoundland and Labrador, Gulf of St. Lawrence and Bay of Fundy - Gulf of Maine). There is likely some mixing of these populations in the winter when less is known about their distribution (Figure 1.).
Figure 1. Adapted from Read’s (2002) Update to the COSEWIC Status Report on Harbour Porpoise Phocoena phocoena (Northwest Atlantic Populations).
There is very little data on patterns of movement within the three Canadian populations with the exception of the western Bay of Fundy where radio-tagging studies have been conducted. There, tracked individuals travelled approximately 50 km per day. The home ranges of such individuals could encompass the entire Gulf of Maine. The Bay of Fundy/Gulf of Maine population is transboundary and tends to move into U.S. waters in the fall. Individuals may return to the same areas on a seasonal basis from year to year. See COSEWIC Assessment and Update Status Report on the Harbour Porpoise Northwest Atlantic population 2003.
COSEWIC Status: Harbour Porpoise (Northwest Atlantic population)
The Northwest Atlantic population of the Harbour Porpoise is currently designated by COSEWIC as a species of Special Concern. The most recent COSEWIC assessment of this species was in May 2003. From April 1990 until May 2003 when it was downlisted to a species of Special Concern this population had been listed by COSEWIC as a Threatened species.
Harbour porpoise were initially listed by COSEWIC due to a significant proportion of the population being accidentally killed each year as incidental bycatch particularly in groundfish gillnet fisheries. The magnitude of this problem may have decreased in recent years due to changes in the groundfish fishery. However, there are still many hundreds or thousands of porpoise that die each year by accidental entrapment in fishing gear. Since there is little known of the population dynamics of Harbour Porpoise, unintentional deaths as bycatch in the fishery are a significant conservation concern.
What Threats Does the Species Face?
There are no estimates of the annual survival rates experienced by the various Harbour Porpoise populations. What data there are on the age distribution of a given population come from samples of dead animals from stranding events or fishing gear entrapments. These data are difficult to interpret as animals dying in this way may not be representative of the general population. Our knowledge of the age makeup and the potential rate of increase of Harbour Porpoise populations remains poor. There is a great deal of uncertainty in our understanding of how much human-induced mortality Harbour Porpoise populations can sustain. Currently, human sources of mortality may pose a threat to the survival of the Harbour Porpoise. There is a concern that prevailing conditions may put the northwest Atlantic populations of Harbour Porpoise at risk of becoming threatened. Potential problems (presented in no particular order) faced by Harbour Porpoise include:
- Entanglement in fishing gear
- Habitat exclusion by Acoustic Harassment Devices
- Habitat degradation and loss from oil and gas activity
- Potential for over fishing to reduce prey base
- Research activities and Eco-tourism
Entanglement in Fishing Gear
The largest known cause of human-induced mortality for Harbour Porpoise is entrapment in fishing gear, mainly bottom-set gillnets. In past decades large numbers of Harbour Porpoise died as fishery bycatch throughout eastern Canada. With recent closures of some groundfish fisheries the magnitude of this threat may be less than in the past. Despite reduced fishing effort, bycatch continues. For example, in Newfoundland and Labrador estimates of numbers caught accidentally by inshore fishing gear during the summer along the south coast, ranged from approximately 700 to 5,300 in 2002 alone .
In the Gulf of St. Lawrence estimates of the number of porpoises killed in fishing gear from 1989, 1990 and 1994 were in the range of 2,000 to 4,000 animals per year. Most deaths occurred during summer in groundfish gillnets.
In the Bay of Fundy, as else where, groundfish gillnets were also the main source of fatal porpoise entrapments. Since 1995 when a cap of 110 by-caught porpoise per year was set, the number of entrapped porpoise deaths declined from the low hundreds to tens of animals. Numbers in the Gulf of Maine were in the low thousands up to 1996 but have since declined to hundreds and in 2001 tens of animals. Declines may not simply be the result of a reduction in the threat level; a reduced number of porpoise would also lead to a reduction in the number of entrapments.
Habitat Exclusion by Acoustic Harassment Devices
There are concerns in the Bay of Fundy that the use of Acoustic Harassment Devices (AHDs) by the aquaculture industry may lead to large-scale exclusion of Harbour Porpoise from their preferred habitat. AHDs are used to scare seals away from aquaculture sites by producing high intensity sounds. These sounds are heard by Harbour Porpoise and appear to scare them away from the area as well. There is potential for a cumulative effect to develop if the use of such devices is allowed to spread through an area.
Increased levels of contaminants in areas of regular use by Harbour Porpoise can lead to elevated levels of contaminants in their body tissues. The large amount of fatty tissue carried by marine mammals makes them susceptible to accumulating concentrations of fat-soluble contaminants that are present in their environment or prey base. High levels of contaminants due to industrial development have negatively affected the health of some whale populations in Canada, for example, the beluga whale population in the St. Lawrence River. It is possible that Harbour Porpoises could accumulate such toxins as well, and this might have negative consequences.
Habitat Degradation and Loss From Oil and Gas Activity
Offshore oil and gas installations may lead to localized habitat degradation and loss through physical disturbance and the use of the ocean as a waste treatment facility. The current Waste Treatment Guidelines allow disposal into the ocean of drilling waste and produced water. These operational wastes contain a variety of contaminants. While limits are imposed on the concentrations of contaminants that can be disposed into the sea there are no limits on the total amounts permitted. Therefore, the potential for cumulative effects is not prevented. With the growth of offshore oil and gas activity there is also a growth in the potential for cumulative negative effects on the quality of habitat occupied by marine life to develop.
The oil and gas industry uses seismic exploration to map areas of potential interest for future oil and gas development and the behavioural and physical impacts of seismic exploration on marine animals are not completely understood. There are no studies of the potential effects of seismic exploration on Harbour Porpoises. Seismic activity could be a source of acoustic harassment or cause displacement of Harbour Porpoises (or their prey) from preferred habitat.
Potential for Over Fishing to Reduce Prey Base
The preferred prey of Harbour Porpoise, particularly herring, are fished commercially. Over-fishing of the preferred prey is therefore possible and could constitute a threat to Harbour Porpoise. While there is no evidence to suggest that this is currently the case, recent large-scale changes to the marine food web suggest the need for caution.
As one of the smaller cetaceans with limited energy reserves, Harbour Porpoise need to feed frequently. They are usually observed in association with prey and the Porpoises’ limited abilities to go without food for long periods are demonstrated each year when numbers of starved juveniles are found dead on the east coast of the U.S. If fishing activity depletes the Porpoises’ preferred prey such that Porpoises must spend more time searching for food, this could also constitute a threat to Harbour Porpoise.
Research Activities and Eco-tourism
Research activities and Eco-tourism –considered relatively benign activities by some – may impact Harbour Porpoise behaviour. Harbour Porpoise are generally considered shy. Development of widespread and intensive human activity in their preferred habitats may pose a threat to their populations. They may be particularly vulnerable when birthing their calves.
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