{"id":38000,"date":"2022-03-14T00:05:29","date_gmt":"2022-03-14T07:05:29","guid":{"rendered":"https:\/\/hakaimagazine.com\/?post_type=custom_news&p=38000"},"modified":"2022-03-11T16:00:31","modified_gmt":"2022-03-12T00:00:31","slug":"killer-whales-scars-tell-a-story","status":"publish","type":"custom_news","link":"https:\/\/hakaimagazine.com\/news\/killer-whales-scars-tell-a-story\/","title":{"rendered":"Killer Whales\u2019 Scars Tell a Story"},"content":{"rendered":"

When southern resident killer whales off the coast of British Columbia and Washington State surface for breath, they show off pointy dorsal fins and their iconic dual black-and-white coloration. But a closer inspection can reveal white scars scratched onto their otherwise sleek backs. These scars are from bite marks\u2014\u201ctooth rakes\u201d inflicted during skirmishes with other killer whales.<\/p>\n

In a new study<\/a>, scientists have shown that by analyzing these scars they can better understand the aggressive behavior at play beneath the surface. And by examining how the prevalence of scarring has changed over several decades, they can see how killer whales\u2019 aggressive interactions have changed over their lifetimes\u2014and even begin to understand why.<\/p>\n

Charli Grimes, a whale researcher at the University of Exeter in England and lead author of the new paper, says southern resident killer whales are \u201cquite placid and quite playful\u201d compared to other groups of killer whales. Scientists have only ever directly seen one case of a southern resident killer whale attacking another killer whale, though as evidenced by the scars, they know that these aggressive interactions must happen readily underwater. Since sightings of aggressive behavior are so rare, Grimes and her colleagues used photographs of tooth rakes as an indirect method for studying aggression.<\/p>\n

Tooth rakes have been looked at in other cetacean species\u2014most notably bottlenose dolphins\u2014for decades. The new study, however, is one of the few to apply the approach to killer whales, and the first using it to study the southern residents. Because the bite marks heal over time, scientists track when the killer whales are accruing new scars.<\/p>\n

Since 1976, scientists with the Center for Whale Research in Washington have been photographing the region\u2019s southern resident killer whales. Using photo analysis software, Grimes and her team quantified the amount of scar tissue borne by 167 different killer whales over a 38-year study period.<\/p>\n

They found that young male killer whales have the highest number of fresh scars, a finding that seemed predictable to the team given killer whale social structures. Southern residents have a matriarchal social structure, says Grimes, and young whales duke it out to establish their spot in the hierarchy and to get first dibs on prey. Young males also spar for females\u2019 attention, she adds.<\/p>\n

But because they had such a long photographic record to analyze, the scientists could take the study a step further. By correlating their scar data with records of salmon abundance through time, they found that changes in salmon availability affect the amount of aggression and scarring.<\/p>\n

Though Grimes and her colleagues originally assumed that the prevalence of tooth rakes would increase when salmon are scarce as the cetaceans compete for their favorite food, they actually found the opposite: more salmon meant more scars.<\/p>\n

\"killer<\/a>

Analyzing rates of scarring shows that southern resident killer whales are more aggressive when salmon, their favored food, is more abundant. Photo by the Center for Whale Research<\/p><\/div>\n

Grimes has a potential explanation for this unexpected finding. \u201cAt times of high salmon availability,\u201d she says, \u201cthe social network of southern residents is more interconnected.\u201d More salmon could lead to bigger aggregations of killer whales, and to more social interactions. Plus, with energy to spare, younger whales may be engaging in rough-and-tumble play, resulting in more scars.<\/p>\n

Todd Robeck, a conservation researcher at SeaWorld Parks & Entertainment, has previously studied aggressive behavior and tooth rakes in killer whales but was not involved in the current study. Robeck\u2019s previous research<\/a> showed that transient (Bigg\u2019s) and northern resident killer whales in the northeast Pacific have a different pattern of scar acquisition\u2014in those populations, older male killer whales have more fresh scars. This confirms, he says, that the different groups have very different social structures and behaviors.<\/p>\n

\u201cThe most interesting thing was that the rake marks were increasing with food,\u201d says Robeck. Although surprising, he says the pattern isn\u2019t entirely unheard of, as many primates are also less aggressive when food is scarce.<\/p>\n

For future studies, the method of analyzing photographs of tooth rakes could also be applied to other populations of killer whales and to tease out the factors that influence aggression. Robeck and Grimes agree that behavioral studies such as this one would be bolstered by drone or underwater footage. By following killer whale behavior beyond what can be observed from above-water photographs, scientists may soon reveal what aggressive behavior actually looks like beneath the waves.<\/p>\n","protected":false},"excerpt":{"rendered":"

When southern resident killer whales off the coast of British Columbia and Washington State surface for breath, they show off pointy dorsal fins and their iconic dual black-and-white coloration. But a closer inspection can reveal white scars scratched onto their <\/p>\n

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