‘Angry’ Seagulls Likely the Cause of Baby-Whale Deaths in Argentina

December 14, 2015 | Joanne Kennell

Sea gull eats blubber from a whales' back
Photo credit: Screen capture from video by geobeats

What is their problem?

If you already don’t like seagulls… well this story isn’t going to change your mind.  I for one know how aggressive they can be.  In the eighth grade while walking home from school eating a sandwich, I was chased and dived-bombed by a flock.  I ran while my friend behind me fell to the ground with laughter.

However, it turns out they are more than just pests that try to steal your french fries at the beach — they pose a serious threat to many animals, including the southern right whale (Eubalaena australis).  According to a new study published in the scientific journal PLOS ONE, 626 baby right whales have died near the Valdés Peninsula off the coast of Argentina between 2003 and 2014, and seagulls likely played a role.

SEE ALSO: Do whales attempt suicide?

What is odd is that the relationship between the kelp gulls (Larus dominicanus) and the right whales started very innocent.  The gulls would just snack on dead skin that floated to the surface during breaching, however several decades ago, the gulls began to peck at resting whales backs as they swam near the surface.  Not only that, they also began to peck at the backs of baby right whales.

In the 1980s, when mother whales were the gulls’ primary targets, the average calf would have two small wounds on its back.  However by the 2000s, the average number of lesions had grown to 20.

"The attacks are very painful and cause large, deep lesions, particularly on the backs of young 2-6 week-old calves," said researchers Vicky Rowntree and Mariano Sironi.  Rowntree is co-director of the Southern Right Whale Health Monitoring Program, director of Ocean Alliance’s 43-year study of the southern right whales of Península Valdés and a research professor at the University of Utah.  Sironi is the scientific director of the Instituto de Conservación de Ballenas in Argentina and advisor to the program.

So why have the attacks on baby whales increased so dramatically?

In the 1990s, right whale mothers began to defend themselves from the birds by keeping their backs underwater when they swam near the surface.  However, baby whales are not able to do this.  "The zero- to three-month-old calves don't know how to keep their backs underwater," said Rowntree to LiveScience. "Their backs are too small to arch, and now, the gulls' primary targets are the newborn calves."

Although it is not entirely clear if the increase in gull attacks did in fact lead to the increase of baby whale mortality, there are a few hypotheses as to how constant harassment from gulls, coupled with the wounds the bird inflict could contribute.

For one, constantly being attacked leaves little time or energy for nursing or playing, both of which are important to baby whales’ health development.  Second, the stress and wounds inflicted by the gulls may inhibit a calf’s ability to fend off threats of dehydration, parasitic infection and hunger.  Researchers learned that the mother and calf right whales spend up to 20 percent of daylight hours avoiding these attacks, which does not allow the mom to produce enough milk to feed her baby.

“The southern right whale population is still only a small fraction of its original size, and now we have reason to worry about its recovery,” Rowntree says. “Our long-term data indicate that the Peninsula Valdes whales were increasing steadily at close to 7 percent per year until recently. Elevated calf mortality is reducing that growth rate substantially. If this continues, we just don't know what will happen.”

Whales are not the only animals that seagulls attack.  Seagulls peck the eyeballs out of young Cape fur seals, and then consume the baby seals’ skin and blubber.

This video explains more about the gulls' impact on the poor whales.



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