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Ancient seabird bones reveal human effects on ocean food chain

Researchers from Michigan State University say that the bones of endangered Hawaiian petrels reveal changes in the open-ocean food chain. According to the U.S. Fish & Wildlife Service’s Pacific Islands Fish and Wildlife Office, the Hawaiian petrel has a dark gray head, and tail, and a white forehead and belly. This bird has a wing span of three feet and measures 16 inches in length.

The researchers examined the bones of Hawaiian petrels – birds that spend a lot of time combing the open waters of the Pacific for their next meal. They discovered that a significant change in the birds’ eating habits, feasting on prey that are lower rather than higher in the food chain, seems to have taken place at the same time as the growth of industrialized fishing.

Researchers are very concerned about the fate of the Hawaiian petrels and any other species that may face similar shifts in diet. Co-author Peggy Ostrom, a zoologist at Michigan State University, said that the bone record is concerning because it shows that open-ocean food chains are being significantly altered because of human influence.

The study is the first to examine whether fishing impacts more than just the targeted species, such as the nontarget- species or entire food webs in the open ocean. The researchers are able to tell what the petrels are eating by studying the chemical makeup of their bones.

The researchers examined the bones’ ratio of nitrogen-15 and nitrogen-14 isotopes. Up until 100 years ago, petrels had high isotope ratios, suggesting that they consumed larger prey. However, following the start of industrial fishing, the isotope ratios decreased, suggesting a species-wide change to a diet of smaller prey.

The Pacific Islands Fish and Wildlife Office notes that adults eat squid, fish and crustaceans and given food to their young via regurgitation.

The bones of this bird help scientists learn more about fishing’s impact on open-ocean animal populations, according to lead author Anne Wiley, a Smithsonian postdoctoral researcher.

While the bones of most marine animals are buried on the ocean floor, co-author Helen James of the Smithsonian Institution and her colleagues have been able to collect more than 17,000 ancient Hawaiian petrel bones from the Hawaiian Islands. If the petrels die in burrows and caves on the Hawaiian Islands, their bones are preserved for many years.

The researchers contend that additional studies need to be conducted to determine exactly how the change in diet is impacting Hawaiian petrels.

Once abundant, the Hawaiian petrel is now considered an endangered species.

The study’s findings are described in detail in the journal Proceedings of the National Academy of Sciences.