photo: Ryan Lowler, Newport Coastal Adventure
The elusive North Pacific Offshore killer whales were first discovered in 1979 when they were spotted off Haida Gwaii. Their current known range spans between Southern California and the Aleutian Islands. Due to their tendency to be far offshore and wary of boats once found, little is known about this unique population of killer whales.
Offshore killer whales were listed under the Species at Risk Act (SARA) in 2003 as a Species of Special Concern. This means that the population is vulnerable to becoming threatened or endangered. Like other killer whales, they are believed to have long lifespans, late maturity, long gestation periods, extended gaps between offspring, and females likely become post-reproductive in their early forties. These all contribute to slow population growth. A Management Plan for the population was released by DFO in 2009.
Source: Fisheries and Oceans Canada: Management Plan for the North Pacific Offshore Killer Whale in Canada. Click to enlarge map.
Studies have allowed scientists to conclude that the North Pacific Offshore killer whales are genetically more closely related to Resident killer whales than they are to Bigg’s (Transient) killer whales. They are also more similar in appearance to Residents than Bigg’s and have the tendency to vocalize frequently as seen in the fish eating killer whales. The tip of the dorsal fin of Offshore killer whales appears to be rounded on the leading edge and tip, more so than in Residents, and different from the pointy tip of a Bigg’s dorsal fin. They tend to have more nicks and scars than Northern or Southern Residents, which likely results from the type of prey they eat. Their saddle patches are predominantly closed or solid, but some have openings of black, as is seen in many Resident killer whales.
When seen, Offshore killer whales have typically been in groups of 20 or more. Based on photo identification, scientists believe that there is a minimum of 280 Offshore killer whales living off the coast of British Columbia. Sightings in coastal and inshore waters have increased in recent years. This may be due to a shift in habitat usage due to changes in prey distribution and/or abundance.
One of the most fascinating aspects of Offshore killer whales is their diet—they eat sharks. Field observations by Dr. John Ford in 2008 and 2009 allowed his scientific team to take samples of the orcas’ “leftovers”, confirming they do in fact eat sharks. Most shark species, like Sleeper Sharks, which the orcas were eating, control their buoyancy in the water by having massive livers full of lipids or fats. In Sleeper Sharks, the liver can account for up to 80% of their total body weight. It’s the fatty liver that the Offshore killer whales consume, as the cartilaginous skeleton and sandpaper-like skin do not hold much nutrition value for the whales.
Source: Research Gate
Learn more about Offshore Killer Whales!
Fisheries and Oceans Canada Species at Risk- Northeast Pacific Offshore killer whales
BC Cetacean Sightings Network- Mysterious killer whales now “threatened”