The Whale Too Big for Its Own Good
For decades, scientists have tried to solve a deadly puzzle: Why can’t highly intelligent blue whales avoid the collisions with ships that are a leading cause of mortality for the endangered marine mammals?
The short answer, according to a first-of-its-kind study, is that they have never learned to steer clear of big objects like ships. The largest animal that’s ever lived, at more than 100 feet long and 320,000 pounds, the blue whale for 30 million years never had to move out of anything’s way.
“The main point for me is that these are animals supremely adapted to surviving in a challenging marine environment, and fast, large ships is something they have not had to deal with or are evolved to deal with,” said Megan McKenna, a coauthor of the study and a researcher with the National Park Service in Fort Collins, Colorado. “There is little opportunity for an animal to learn about this threat, since a ship strike will often be fatal.”
The scientists used suction cups to attach GPS trackers and dive-logging recorders to blue whales that frequent the ocean near Los Angeles, a feeding hot spot for the animals between May and October. Researchers followed the whales’ movements for 24-hour periods and cross-referenced the data with information about boat traffic, including the tonnage and speeds of ships passing through the area.
“Los Angeles is one of the busiest ports in the world, so we knew this would be an ideal place to study the interactions of whales and ships,” said McKenna, a member of the interdisciplinary team that conducted the research, which was published in the journal Endangered Species Research. In 2007, for instance, ship strikes killed four of California’s estimated population of 2,200 blue whales.
The scientists observed 20 ships passing nine whales, at distances ranging from 65 yards to more than 1.9 miles. In each of these instances, the whales exhibited behavior similar to what they do during the tagging process—not moving much. Whales have to dive at least 100 feet deep to avoid a ship’s propellers.
“We found no evidence for horizontal movement away from passing ships and a dive response that was slow and shallow, which leaves whales susceptible to ship strikes,” said McKenna.
Other scientists are developing technology to predict where blue whales will congregate so ships can be alerted to their presence to minimize the risk of collisions.
McKenna said blue whales may need to be prioritized as having a greater risk of ship strikes than other species. That may mean rerouting ships to avoid the seasons and places where blue whales travel the most.
The researchers’ future efforts will investigate how other species, such as humpback whales, react to ships.