Gray whales continue to wash up dead and emaciated, but causes remain elusive. Now scientists are taking another look at the mystery.
Roughly 40,000 gray whales migrate through the waters off the West Coast from mid-November through mid-April each year. Although their numbers have steadily increased in recent decades, the number of whale carcasses washing up along the U.S. West Coast has been on the rise, as has the incidence of whale entanglement in fishing gear.
To investigate the causes of the whale deaths, researchers from the Oregon State University (OSU) and the National Oceanic and Atmospheric Administration (NOAA) have analyzed data collected between 2009 and 2012, combining the findings from multiple sources, including ship-based satellite observations from the NOAA Fisheries Office in Monterey, California and the Marine Mammal Commission’s Marine Mammal Program. The team found that a substantial portion of the whales’ deaths had nothing to do with entanglement in fishing gear. Although whale entanglement in fishing gear has increased, whale deaths generally fell short of the increase, instead continuing to decline.
What’s more, the number of reported whale entanglements declined steadily in the period from 2009 to 2012. This suggests that whalers are taking more measures to avoid entanglements, or that other changes in whale habitats are reducing the danger of entanglements.
“We found that as the number of whale deaths declined, so did the number of reported entanglements,” says Dr. Jeff Pettijohn, professor of oceanography and lead author of an article on the study, published today in the journal Scientific Reports. “And we showed that even when there were fewer reported entanglements, still greater-than-expected increases in the total number of dead whales were recorded.”
Since the early 1970s, the West Coast gray whale population has declined by about 40 percent. NOAA estimates that there were 20,