Kelp Gulls: Are They Responsible for the Increase in Southern Right Whale Deaths?

Using their sharp beaks, hungry and aggressive Kelp Gulls routinely gouge southern right whales in the back and feed off their skin and blubber – but are they responsible for the increasing number of calve deaths over the last decade? That was the question researchers from the University of Utah and the Programa de Monitoreo Sanitario Ballena Franca Austral in Argentina set out to answer in examining the deaths of over 600 southern calves. The whales were found dead near the Península Valdés calving ground in Argentina between 2003 and 2014, according to the university's news release.

Kelp Gulls breed along coasts throughout much of the southern hemisphere, including Argentina, Australia, New Zealand, Africa, Madagascar, Ecuador and Brazil, where right whale calves begin their lives. That's the main reason why the number of southern right whales wounded by Kelp Gulls near Argentina has increased from two percent to 99 percent over the course of four decades.

For their study, researchers used aerial survey photographs, which revealed that Kelp Gulls prefer to target mother-calf pairs. The resulting wounds to the whales often lead to dehydration, impaired thermoregulation, and energy loss. Moreover, stressed mother whales spend less time nursing their young, playing with them and resting.

"It is tempting to look at the correlation in time and think the gull-inflicted wounds must be a contributing factor to calf deaths, but despite a lot of work we still don't have convincing evidence for any plausible mechanism," Dr. Carina Marón, one of the study researchers from the University of Utah, said in the release. "One possibility is that increased stress is making young calves more vulnerable to a variety of other factors. We like that idea, but it won't be easy to prove."

In total, researchers noted gull-inflicted lesions on 2680 living mother-calf pairs between 1974 and 2011.

The study's findings were recently published in the journal PLOS ONE.

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