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Natalie's blog, Part 2: Marine mammals of British Columbia: Killer whales (Orcinus orca)

Friday, 29 July 2016 09:13
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Natalie's blog, Part 2: Marine mammals of British Columbia: Killer whales (Orcinus orca) © Vancouver Aquarium, NOAA Fisheries. Taken by UAV from above 90 feet under Fisheries and Oceans Canada research permit and Transport Canada flight authorization.

 

At present, only one species of killer whale (Orcinus orca) is recognized globally and there are thought to be more than 50,000 individuals that can be found across the globe. The killer whale populations around the coast of British Columbia are the most studied cetaceans in the world and it is where I have spent the last three months in order to learn more about them. In British Columbia, there are three ecotypes: Offshore, Resident, and Bigg’s (previously called Transients) killer whales. These ecotypes are all distinct from one another in morphology, behaviour, acoustics and genetics. They do not communicate with each other, socialise or interbreed. There is now a great deal of work which suggests that they might actually be separate species of killer whales.

The offshore killer whales number approximately 300 individuals but they are rarely encountered and so they are the least well known. They travel in large groups and are acoustically active, feeding on fish and sharks. Their diet on sharks which have rough skin causes their teeth to get worn right to the gum line. Bigg’s killer whales are mammal-eaters, primarily feeding on harbour seals, harbour porpoises and sea lions. There is thought to be approximately 500 individuals, with about 300 of these regularly occurring in the inshore coastal waters. They have large home ranges, with some showing a degree of site fidelity to a few locations, visiting every year. However, their movements are unpredictable and there are still a lot of unanswered questions about them. The resident killer whales are the most studied having predictable distributions, particularly in the summer where their movements are dictated by the presence of Chinook salmon. There are two populations of resident killer whales, the northern residents (in the Johnstone Strait) and the southern residents (near the San Juan Islands and Haro Strait). Overall, the number of northern residents is 254 and the southern residents is just 84. The Southern resident population in particular was severely reduced during the 1970s by captures for the aquarium trade. Their number is still low and they are listed as Endangered. Resident killer whales live in extremely close family units, called matrilines, with sons and daughters living with their mother for life, sometimes up to three of four generations all living together, every single day for life.

Due to the ground breaking work by the late Dr Michael Bigg, it has been possible to identify nearly every single killer whales in the British Columbia by use of photos of their dorsal fins and saddle patches which are all unique. For decades, killer whales have been studied using dorsal fin photos, mostly by boat based surveys to understand their social organisation, genetics and vocal dialects. However, Vancouver Aquarium’s Dr Lance Barrett-Lennard, and his colleagues Dr John Durban and Holly Fearnback (NOAA) are leading the way on novel insights into the health of killer whales in British Columbia using drones. Flying above the whales to take photos of them provides a different perspective on the whales. Lance and his colleagues are able to assess the condition of each whale by measuring the length and width of the whales using a technique called photogrammetry. Whale condition is linked to foraging success, and so the more the killer whales can find the Chinook salmon that they feed on in the summer, the better their condition will be. What this essentially means is that we can determine how fat and healthy they are or how close to starvation they might be. The hope is that his work continues for many years in the future and becomes a tool for long-term monitoring to help identify when the whales are nutritionally stressed, before they begin to starve. Working with fisheries managers, this could mean that if the killer whales are showing signs of low food source, fisheries could be restricted in the areas that are most important to them so they have access to prey.

I spent the best part of June and July looking through thousands of these photos identifying each individual so that Lance and his team can track inter-annual variability for each individual and identify the ones that are losing weight. This technique can also be used to identify pregnant females from as early as 5 months and so it can also help scientists calculate the rates of miscarriage in killer whales and also keep an eye on our soon-to-be mums.

 

For more information on the marine mammal research being conducted by scientists at Vancouver Aquarium click here: http://www.vanaqua.org/act/research/cetaceans

 

 

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