Unalaska, AK – The decline in Aleutian sea otter populations is affecting what bald eagles eat. A new study published in the journal Ecology this month compares the eagles' eating habits from before and after the sea otter decline. The US Geological Survey study's lead biologist, Dr. Bob Anthony, explained that the species are linked in two different ways. The first is directly eagles often eat sea otter pups when the adults dive into the water to gather food. The species are also linked through a long ecological chain.

"Sea otters eat urchins, which eat kelp and the kelp beds are habitat for kelp-inhabiting fishes which bald eagles prey upon," Anthony explained. "So when the otter populations declined, there were an abundance amount of sea urchins which foraged on the kelp and basically removed kelp beds from most of the Aleutian Islands. As a result most of the kelp-inhabiting fishes disappeared so they disappeared from the eagles' diet, as did sea otter pups."

The eagles had to start eating more sea birds to supplement their diets. Anthony hypothesizes that this shift might explain the increase in the eagle's reproductive productivity.

"One possible hypothesis is, birds have a higher caloric content per unit mass than do fish, so it's possible that the eagles might have been in better physical condition and therefore able to produce more young," he said.

The study compared data sets from the early 1990s and the early 2000s. Anthony, who has studied bald eagles for more than 30 years, said the data was originally gathered for completely different research projects and just happened to reveal this connection.

It is uncertain why sea otter populations are declining, but Anthony's research partner, ecologist Jim Estes, hypothesizes that the sea otters are being eaten by foraging killer whales. The sea otter population in the Aleutians has declined from about 75,000 to 8,700. They were listed as threatened in 2005.