May 14, 2013
Changing Eating Habits Of The Hawaiian Petrel And Other Sea Birds Concern Scientists
redOrbit Staff & Wire Reports - Your Universe Online
Changes in the eating habits of endangered Hawaiian petrels have scientists concerned about the impact that the growth of industrialized fishing will have not only on the seabirds but upon other species of animals as well.
Researchers from Michigan State University (MSU) and the Smithsonian Institution (SI) looked at both ancient and modern remains of the birds, which spent much of their lives foraging for food in the Pacific Ocean. They discovered the petrels have started eating prey that are lower on the food chain rather than higher.
“Our bone record is alarming because it suggests that open-ocean food webs are changing on a large scale due to human influence,” co-author Peggy Ostrom, a zoologist at the East Lansing, Michigan-based university, said in a statement. “Our study is among the first to address one of the great mysteries 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.”
The diet of the birds can be determined by studying their bone chemistry, the researchers said. By analyzing the ratio of nitrogen-15 and nitrogen-14 isotopes, experts can determine which level of the food chain the birds are preying on for their food. The larger the isotope ratio, the bigger the creatures the petrels have been targeting.
“Between 4,000 and 100 years ago, petrels had high isotope ratios, indicating they ate bigger prey,” MSU officials explained. “After the onset of industrial fishing, which began extending past the continental shelves around 1950, the isotope ratios declined, indicating a species-wide shift to a diet of smaller fish and other prey.”
The majority of research into the impact of fishing focuses on the coastal areas, while the open waters cover almost half of the planet´s surface, the researchers explained. However, due to a lack of historical record, fishing´s impact on most open-ocean animal populations remains entirely unknown at this point in time.
“Hawaiian petrels spend the majority of their lives foraging over vast expanses of open ocean,” said lead author Anne Wiley, a postdoctoral researcher at SI. “In their search for food, they´ve done what scientists can only dream of. 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.”
“Further studies are needed to explore how the shift down the food chain is affecting Hawaiian petrels. For a coastal seabird, however, a similar shift in diet has been associated with decreases in population — bad news for a federally protected bird,” researchers from Michigan State added.
The research was funded in part by the National Science Foundation (NSF).
Image Below: Excavated bones of Hawaiian petrels — birds that spend the majority of their lives foraging the Pacific — show substantial change in the birds' eating habits. Credit: Brittany Hance, Imaging Lab, Smithsonian Institution.