Some of you may have heard of the dead cetacean that had washed ashore in front of Hollyhock last weekend and wondered about what had happened to it. It was a harbour porpoise (Phocoena phocoena) and although the sexes are hard to tell apart, we think this one was female due to its large size and we could just make out the teat openings on either side of the genital slit. It was 1.9 metres from tail fluke to nose, 1 m in circumference just ahead of the dorsal fin and an estimated weight of about 60 kg.
With darkness coming on Sunday evening, Samantha called the cetacean hotline 1 800 465-4336 who passed the information on to the Department of Fisheries and Oceans. We collected the porpoise from the beach to prevent it from being further damaged by the wolves that were seen feeding on it earlier in the day or it being washed out to sea, with the intention to preserve its skeleton.
The next day we photographed and measured it and sent this information to the DFO. Being protected under the Marine Protection Act, DFO will provide us with a letter confirming it had been collected legally. We could not confirm the cause of death because the carcass had been damaged by wolves and eagles but there did seem to be a long, clean gash that may have been caused by a propeller of perhaps by orca and orca were indeed seen from the Cortes ferry that very day.
The porpoise has now been buried under a layer of horse poop and lined underneath with wire mesh so that the flesh will rot away and we can collect the bones for a display at the Cortes museum. The fact that the spinal processes of the thoracic vertebrae were gnawed off by wolves will just add to the display story.
Here is some additional information on harbour porpoises taken from the wild whales, BC cetacean sightings network website www.wildwhales.org
Harbour porpoise have a circumpolar distribution throughout the temperate and boreal waters of the northern hemisphere. Three isolated groups are recognized: north Pacific, north Atlantic, and Black Sea- Sea of Azov. They prefer near coastal waters although occasional sightings in deep water are recorded (see map below). They are frequently seen in BC’s many inlets and fjords. Infrequently, they may also be spotted in brackish rivers.
Harbour porpoise are thought to remain resident for extended periods in one area. They are a very difficult animal to spot and individually identify due to their small dorsal fin, cryptic behaviour, and minimal surface activity.
Harbour porpoises are generally seen in small groups between 1 to 3 animals. Larger congregations of several dozen harbour porpoises are sometimes observed, particularly in spring or fall. These large groups are thought to be feeding on prey that is concentrated by strong, seasonal tides. Harbour porpoise feed on small schooling fishes, such has herring, eelpouts, hake, sandlance, salmon and cod, as well as squid. Calves may also feed on euphasiids between weaning and when they commence eating fish.
Male and female harbour porpoises look similar, and while females often are slightly larger, it is difficult to tell the two sexes apart. Harbour porpoises are often described as promiscuous and polyandrous with significant sperm competition. Males have a marked development of the testes seasonally, which may weigh up to 6% of their body weight during the mating season. In British Columbia, mating appears to peak in late summer to early fall. Females are pregnant for 7 to 11.4 months. A single calf is born mainly from May to September. Nursing may occur for up to 8 to 12 months, but is significantly reduced after the first few months. It is unknown when harbour porpoises reach sexual maturity in the north Pacific, but in the north Atlantic it is around 3-4 years. Females have a calf every 1 to 2 years, and both sexes may live to 13 years.
Hybridization between Dall’s porpoise and harbour porpoise occurs occasionally in BC waters with harbour porpoise as the paternal parent and Dall’s porpoise as the maternal parent. Hybrids tend to appear more similar to Dall’s porpoise in body shape, diving characteristics and behaviour, but they lack the white side patches and the colouring is more similar to the harbour porpoise.
Transient (mammal-eating) killer whales and sharks may prey on harbour porpoises, although evidence of the latter has only been observed once in British Columbia. Harbour porpoises are the most frequently reported stranded cetacean in British Columbia though reasons for their stranding are various. In many parts of their range, harbour porpoise populations are heavily impacted by entanglement in fish nets, particularly gillnets. They also appear to very sensitive to noise and other human impacts in more urban areas.
STATUS IN CANADA_COSEWIC: Special Concern (2003)_Reason for Designation: They appear to be particularly sensitive to human activities, and are prone to becoming entrapped and killed in fishing nets. They are a short lived shy species that are now rarely seen at the highly developed areas of Victoria and Haro Strait. Continued development and use of its prime habitat by humans are some of the main threats. They are displaced by underwater noise, and could be affected by contaminants in their food chain.