By Nadine Pinnell and Doug Sandilands
One of the smallest and shyest cetacean species in British Columbia, harbour porpoises (Phocoena phocoena) were recently listed as a species of special concern by COSEWIC (the Committee on the Status of Endangered Wildlife in Canada). In a previous story, we reviewed various aspects of harbour porpoises’ ecology and natural history (see “Harbour porpoises listed as Special Concern“). In this story, we summarize threats facing harbour porpoises in British Columbia face, exploring the reasons for COSEWIC’s listing.
Changes in population distribution and abundance
Few data on the size or distribution of harbour porpoise populations in the coastal waters of British Columbia are available. Anna Hall, a graduate student at the University of British Columbia, has identified the junction of Juan de Fuca and Haro Straits as critical habitat for the southern Vancouver Island harbour porpoise population (Hall 2003). This is also an area that has seen significant increases in marine traffic and coastal development over the past fifty years. According to anecdotal evidence cited in an update status report for COSEWIC, harbour porpoise abundance in southern British Columbia declined between the 1940-50s and 1980 (Baird 2004). The fact that area populations appear to be smaller than historical ones may reflect the impacts of increased human activity in this area on harbour porpoise populations.
In carrying out surveys for harbour porpoises throughout the year, Hall (2003) found that harbour porpoise abundance in southern Vancouver Island area fluctuated seasonally. More porpoises used the area from April to October than during the rest of the year. This fluctuation could be associated with seasonal prey movements or calving, which occurs in the late spring and summer. Unfortunately, it means that porpoise abundance in the area is highest at times when marine traffic and other human activities in the area are also most intense, increasing the likelihood that porpoises will be impacted by these activities.
Noise and harbour porpoises
In its status assessment, COSEWIC identified development and human use of prime habitat as two major threats to harbour porpoises in British Columbia (COSEWIC 2003). Increased underwater noise levels from such activities can interfere with harbour porpoises’ ability to use echolocation to locate prey and may even displace them from otherwise suitable habitat areas. Research on captive harbour porpoises at the Harderwijk Dolphinarium in the Netherlands has shown that they have exceptionally sensitive hearing across a broad range of frequencies, hearing a wider range of sounds from greater distances than other species of dolphins (eg. bottlenose dolphins) previously studied. Thus harbour porpoise populations may be disproportionately impacted by “noisy” marine activities such as shipping, mineral exploration, construction, and equipment operation, which are common in the coastal inshore habitat areas they prefer.
Harbour porpoises’ reactions to Acoustic Harassment Devices (AHDs) used in aquaculture demonstrate the impact underwater noise can have on local porpoise populations. In the mid-1990s, AHDs were commonly attached to the nets of salmon farms in BC. These devices broadcast high amplitude sounds (~198 decibels) underwater in the hopes of keeping harbour seals and other pinnipeds away from net pens. [The threshold of pain for human hearing occurs between 130 and 140 decibels.] Unfortunately, researchers found that the abundance of harbour porpoises in the area near the farms declined precipitously when the AHD was active, with the impact of the AHD extending as far as 3 km from the net pen (Olesiuk et al. 2002) . Since salmon farms are situated in the same shallow waters that harbour porpoises prefer, the use of these devices has the potential to severely limit the habitat available to harbour porpoises. Some salmon farms have discontinued use of these devices since their effects on cetaceans have become more widely known, yet no regulations currently prohibit their use.
Harbour porpoises worldwide seem extremely vulnerable to entanglement in fishing nets resulting in death by drowning. Their preferences for living in inshore areas and eating commercially important fish such as herring may make them especially prone to becoming bycatch in local fisheries. Since many of harbour porpoise’s prey items live on or near the ocean floor, they are especially vulnerable to entanglement in bottom-set gill nets.
The International Union for the Conservation of Nature (IUCN) has suggested that the single most important action for protecting harbour porpoises worldwide is to reduce their incidental take in gillnets (Hall et al. 2002). In British Columbia, harbour porpoises have been killed in salmon and dogfish drift gill net fisheries, salmon troll, and hake trawl fisheries (Baird 2003). A survey of commercial license holders led researchers Anna Hall, Graeme Ellis, and Andrew Trites (2002) to estimate that between 11 and 102 harbour porpoises die in British Columbia waters every year as a result of the salmon gill net fishery. One method for reducing bycatch of harbour porpoises and other cetaceans is to attach “pingers,” acoustic alarms, to nets so that cetaceans avoid them. Researchers (Trippel et al. 1999) working in the Bay of Fundy found that harbour porpoise by-catch declined by 77% in nets equipped with “pingers”.
However, neither federal nor provincial regulations currently require the use of “pingers” in B.C. fisheries, and the section of the federal Fisheries Act that deals with marine mammals does not address cetacean bycatch.
Stranding and ship strike
Stranding is also an issue for harbour porpoises. They are the most common cetacean stranding occurring along the BC coast (Baird and Guenther 1995), with most strandings occurring between April and September. Most strandings are of dead individuals. Unlike other cetaceans, live harbour porpoise strandings are not common. Natural mortality and harbour porpoises’ preference for inshore habitats may account for the relatively high incidence of harbour porpoise strandings. However, ship strike incidents may also account for some strandings. Harbour porpoises’ low profile and inconspicuous behaviour can make them difficult to spot; they may be especially vulnerable to ship strike, especially when larger waves obscure their small dorsal fins.
Toxins are also a threat to harbour porpoises. Chemicals such as PCBs and DDT from industrial processes and agricultural and household activities that enter the ocean often do not decompose or break down. These toxins are ingested by small organisms and fish, which are then eaten by cetaceans such as harbour porpoises. As harbour porpoises consume many fish daily, effectively ingesting many small doses of toxins, contaminants are concentrated in porpoises. Harbour porpoises in the Strait of Georgia have the highest levels of dioxins and furans found in local cetaceans as well as high levels of organochlorines and heavy metals (Baird 2003). These high toxin levels could affect porpoise reproduction, immune function, and endocrine function, although it is not currently clear how they impact harbour porpoises in BC. Marine debris may also impact harbour porpoises as juvenile porpoises may mistakenly ingest debris and die as a result.
How can I help reduce threats to harbour porpoises?
1. Let us know if you see a harbour porpoise. Watch for small, dark, triangular dorsal fins that surface smoothly the next time you’re out on the water. Remember that harbour porpoises generally do not lift their bodies out of the water, tend to travel alone or in pairs, and are small, dark cetaceans. By reporting your sightings of harbour porpoise or any other type of cetacean, you are gathering information that will help identify important habitat areas and give these species the protection they need.
2. If you do see a harbour porpoise while out on the water, observe the Be Whale Wise guidelines: slow down, don’t approach closer than 100 metres, and avoid approaching it from the front or behind.
3. If you see a harbour porpoise (or any other cetacean) entangled in fishing gear or other debris, call Fisheries and Oceans Canada at 1-800-465-4336. They will be able to call upon experts such as those at the Vancouver Aquarium to help disentangle the porpoise.
4. Make sure that all of your lines, nets, and other gear are properly stowed when you are out on the water so that they cannot pose a hazard to cetaceans or other marine organisms. If you see discarded netting or abandoned fishing gear adrift and you are able to safely access it, please remove it from the water and discard it properly on land.
5. Help reduce the number of toxins entering the ocean and contaminating the marine environment. Avoid using bleached paper and pesticides and make sure oil and household toxic waste products are disposed of properly.
Baird, R.W. 2003. Update COSEWIC status report on the harbour porpoise Phocoena phocoena (Pacific Ocean population) in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa. 1-22 pp. [PDF]
Baird, R.W. and T.J. Guenther. 1995. Account of harbour porpoise (Phocoena phocoena) strandings and bycatches along the coast of British Columbia. Reports of the International Whaling Commission Special Issue 16:159-168. [abstract]
COSEWIC 2003. COSEWIC assessment and update status report on the harbour porpoise Phocoena phocoena (Pacific Ocean population) in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 22 pp. [PDF]
Hall, A.M. 2004. Seasonal Abundance, Distribution and Prey Species of Harbour Porpoise (Phocoena phocoena)in Southern Vancouver Island Waters. M.Sc. thesis. University of British Columbia, Vancouver, BC. 109 pp. [PDF]
Hall, A., G.E. Ellis and A.W. Trites. 2002. Harbour porpoise interactions with the 2001 selective salmon fisheries in southern British Columbia and license holder reported small cetacean by-catch. Selective Salmon Fisheries Science Program Report. Fisheries and Oceans Canada. [PDF]