by Caitlin Birdsall
It was almost time to wrap up another day whale watching in the Johnstone Strait in early September 2007, when a call came in over the radio of an incoming group of killer whales. The passengers aboard the vessel M/V Lukwa of Stubbs Island Whale Watching had already seen resident killer whales earlier in the trip, but were drawn away from port and back out into Blackfish Sound due to the unusual nature of the call: the group was big, but the vessel spotting them couldn’t identify which whales they were. What they were lucky enough to find was a large group, 50 plus whales, coming out of Queen Charlotte Strait. Watching the dispersed group pass into Blackfish Sound, the captain and naturalist couldn’t pick out a single animal they knew; contrary to their first guess, this was definitely not a ‘super pod’ of the well-known northern residents. The animals were unfamiliar, and many had scars and nicks all over their fins and bodies – one animal’s dorsal fin was entirely severed. Curious, the whale watchers dropped their hydrophone into the water, and their questions were answered instantly. Through the speaker came a cacophony of unusual vocalizations. The whales passing them by, chatting animatedly underwater, were the little known, seldom seen, offshore killer whales.
Listen to offshore killer whales:
[audio:offshore.mp3]
The first offshore killer whales were not seen in British Columbia until 1979 and it was not until the late 1980s that they were described as a separate eco-type from the resident and transient killer whales. As the name implies, the ‘offshores’ tend to occupy the waters around the continental shelf, though increasingly they are being spotted closer to shore, like the above sighting in Johnstone Strait. In 1992, a large group of 75 unidentified offshore killer whales also appeared near Victoria. This event caused quite a stir, but sightings of these animals are still infrequent. The BC Cetacean Sightings Network database has only 69 reports of offshore killer whales, and only 37 of those are ‘certain’ sightings.
Offshore killer whales are genetically distinct from both the resident and transient populations, and are believed to occupy a separate ecological niche. Although offshore killer whales generally have a more rounded, blunt appearance to their dorsal fin and are smaller, with less dimorphism between sexes, most observers would find it difficult to distinguish them from resident or transient killer whales. These whales also appear to be very far ranging, in their 2008 paper on offshore killer whales Dahlheim et al calculated some animals moving up to 4,345km between Dutch Harbour, Alaska and Dana Point, California.
Observations of offshore killer whales feeding are few and far between, however their diet is thought by most researchers to be primarily fish. Observed groups are often large (50-80 animals have been seen at a time) and acoustically active, more similar to resident (fish eating) killer whales than the transient (marine mammal eating) killer whales, who rely on quiet and stealth to pursue their prey. In 2006, Ian Jones published a report in Marine Mammal Science describing an offshore killer whale feeding on a Pacific halibut near the Queen Charlotte Islands. Futhermore, their bodies may also hold more clues to their diet: they are frequently seen with significant scars and nicks, and their teeth often appear very worn down. Researchers believe these clues suggest that offshore killer whales feed primarily on large sharks, since the sharks’ rough skin would wear down their teeth, and a shark would put up a fight during capture that could inflict damage. These assumptions were confirmed when in May 2008, killer whale researchers Dr John Ford and Graeme Ellis made an exciting discovery. While surveying humpback whales near Langara Island, they encountered a small group of offshores actively preying on sharks, bringing pieces of them to the surface and sharing them with others in the group! These field observations, although rare, are helping us to learn more about this enigmatic population.
While their diets are still somewhat of a mystery, researchers do know for sure that, like all other north east Pacific killer populations, offshore killer whales are in trouble. This November, at the Committee on the Status of Endangerd Wildlife in Canada (COSEWIC) meeting in Ottawa, offshore killer whales were designated as ‘threatened’. By definition this now means that they are considered “A wildlife species that is likely to become an Endangered species if nothing is done to reverse the factors leading to its extirpation or extinction”. While their population of approximately 279 individuals is thought to be stable, with only 120 mature animals and serious threats facing them, these small numbers could easily be decimated.
Like all eco-types of killer whales, a major concern for offshores is their exposure to contaminants in their environment. Similar to transient and resident killer whales, preliminary data shows that offshores have high levels of persistent organic pollutants (POPs) in their blubbler. As offshores may be feeding on longer lived species of fish (sharks, rockfish) that accumulate higher levels of toxins than other short-lived species, offshores may be more at risk. PCBs, PBDEs, DDT and other chemical contaminants have long-term adverse effects on health and reproduction of these animals. Killer whales are slow reproducing animals normally, and a decrease in their already low levels of offspring could have a significant effect on their population. See our previous news story here to learn more about chemical contaminants, killer whales, and what you can do to help.
Also of concern for offshore killer whales is the potential hazard of oil spills. Offshores, possibly more than either resident or transient killer whales, have habitats that overlap with major shipping lanes, making them more likely to encounter a toxic spill. Their observed behaviour of travelling in large aggregations also means that a disastrous spill could potentially impact a large percentage of their population at one time. To help mitigate this threat, all citizens can reduce their demand for oil by changing their commute from cars to public transport or bike, buying local products whenever possible, and conserving energy in your home through energy efficient lighting and appliances.
While many of the threats facing offshore killer whales seem overwhelming, the new COSEWIC designation of ‘threatened’ means that mitigating these threats does not solely depend on the green actions of coastal citizens. This summer, the designation will be presented to the Minister of Fisheries for listing under the Species at Risk Act (SARA), federal legislation that would require a Recovery Strategy to be created. Previously this population was listed as ‘special concern’ in 2001 and as a result a Management Plan for offshore killer whales was drafted in April 2008. The Management Plan was clear in highlighting the fact that many details on the natural history and biology of offshore killer whales are lacking; a fact that will make management and recovery a complicated task.
To begin down the road to recovery, scientsists and researchers are working hard to answer the many questions regarding offshore killer whales and B.C. coastal citizens and mariners can help. By reporting all killer whale sightings to the BC Cetacean Sightings Network, researchers can learn more about their movements, distribution and abundance. Click here to help by reporting your sightings.
For more information:
Killer whale natural history
Draft Management Plan for offshore killer whales
Recovery strategy for northern and southern resident killer whales
Recovery strategy for transient killer whales
COSEWIC
The COSEWIC/SARA listing process
Species At Risk Act (SARA)
Peter Ross’ article ‘Fireproof killer whales’ on toxin accumulation in killer whales
Offshore killer whales: Dalheim, M.E., A. Shulman-Janiger, N.Black, R.Ternullo, D. Ellifrit, K.C. Balcomb III. (2008) Eastern temperate north Pacific offshore killer whales (Orcinus orca): Occurence, movements, and insights into feeding ecology. Marine Mammal Science 24(3): 719-729.
Jones, I.M. (2006) A Northeast Pacific offshore killer whale (Orcinus orca) feding on Pacific halibut (Hippoglossus stenolepis). Marine Mammal Science 22: 298-200. [PDF]
Jackie Hildering www.earthlingenterprises.ca
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