Endangered Hawaiian Petrel Bones Reveal Human Impact on World's Seas

At one point, the Hawaiian petrel was abundant. It roamed the seas as it fished for food. Now, the bird is endangered; yet its ancient remains are allowing scientists to learn a little bit more about how our seas have changed over the years.

The endangered Hawaiian petrel is a bird of the open Pacific. It spends most of its life among the waves, feeding on squid, fish and crustaceans. Yet between March and October, the petrel returns to the Hawaiian Islands of Maui, Lana'i and Kaua'i in order to breed. There, the creature nests in a burrow in a remote, montane location. This can include along large rock outcrops, under old lichen-covered lava or in soil beneath dense vegetation. The petrel lays just one white egg within this burrow, which helps explain why the number of individuals has declined in recent years.

Because this bird feeds mainly in the open ocean, it makes it a prime candidate for study. The petrel's diet is recorded in the chemistry of its bones, which means that remains can tell researchers quite a lot about the bird's foraging patterns in the past. It can also allow scientists to potentially see how human activities have affected the composition of fish in the ocean.

During the course of the study, the researchers studied the petrel bones' ratio of nitrogen-15 and nitrogen-14 isotopes. This, in turn, allowed them to tell what level in the food chain the birds were feasting--the larger the isotope ratio, the bigger the prey.

"Our bone record is alarming because it suggests that open-ocean food webs are changing on a large scale due to human influence," said Peggy Ostrom, co-author of the paper, in a news release. "Our study is among the first to address one of the great mysterious of biological oceanography--whether fishing has gone beyond an influence on targeted species to affect nontarget species and potentially, entire food webs in the open ocean."

In fact, the researchers made some disturbing findings. Between 4,000 and 100 years ago, petrels had high isotope ratios; this means that they ate bigger prey. Yet after the onset of industrial fishing, which began extending past the continental shelves around 1950, the isotope ratios declined. This indicated that the petrels were shifting their diet to smaller fish and other prey.

"In their search for food, they've done what scientists can only dream of," said lead author Anne Wiley in a news release. "For thousands of years, they've captured a variety of fish, squid and crustaceans from a large portion of the North Pacific Ocean, and a record of their diet is preserved in their bones."

The findings show the impact that fishing is currently having on the world's oceans and the fact that species throughout the food chain are being affected. It also reveals that steps should be taken in order to help preserve fisheries in order to prevent them from collapse.  Currently, more research needs to be conducted to see how this shift down the food chain is affecting the endangered Hawaiian petrels.

The findings are published in the journal Proceedings of the National Academy of Sciences.