New study from Argentina: Gulls are feasting on living whales

The UC Davis School of Veterinary Medicine and Karen C. Drayer Wildlife Health Center do cutting-edge work all around the world. A recent example from Argentina reveals that Kelp gulls are wounding living Southern right whales at an ever-increasing frequency.

UC Davis Wildlife Veterinarian Dr. Marcela Uhart co-authored the study that tracked wounds on the backs of living and dead southern right whales at their calving grounds in Argentina. The gulls eat skin and blubber from the whales' backs when they surface to breathe. For the gulls this is a high-energy source of food, easily accessible in the winter months.

Since gull attacks were first observed in the 1970s, lesions have increased every decade until they were visible in almost every animal by the 2000s. Over time, the actual number of lesions on individual animals shifted from mothers to calves.

"Mothers, who return to the birthing grounds every three years or so, have learned to protect themselves by resting with their heads and tails up and the rest of their body submerged," said Dr. Uhart. "Calves have not learned this and are at greater risk for attack."

In recent years calf mortality has been unexpectedly high at Peninsula Valdés, which is the only place in the world where this kind of gull harassment of right whales has occurred. But it is not yet clear if or to what extent these attacks are contributing to calf deaths. The study does suggest, however, that the attacks are costing the calves precious energy, as well as causing pain and discomfort.

For calves, avoidance behaviors include swimming faster and surfacing to breathe without exposing their backs. Both of these behaviors mean they are investing more energy in avoidance and less in playing, resting, and nursing. Wound healing also diverts essential resources needed for normal growing and development.

Not mentioned in the paper is the inappropriate handling of fishing and urban waste by regional municipalities and fisheries, which are thought to be responsible for artificially increasing the gull population over the past 45 years.

Want to dive deeper into this issue? View the publication at PLOS ONE (open access).



Banner photo: kelp gull pecking skin and blubber from southern right whale. Photo courtesy of Mariano Sironi, Instituto de Conservación de Ballenas.