Blue whales, the world's largest animals, frequent waters off California that overlap with some of the United States' busiest shipping lanes, according to a new study that suggests ship strikes are contributing to the whales' stagnating population numbers.
Blue whales spend their summers in the shallow waters of marine sanctuaries surrounding the Farallon Islands and Channel Islands, offshore of San Francisco and Los Angeles, respectively. Scientists tagged blue whales and monitored their movements via satellite between 1993 and 2008, delineating core areas of use. Commercial shipping lanes intersect with these whale hot spots, sometimes resulting in fatal ship strikes.
Ships struck and killed three blue whales in southern California alone in 2007, says study co-author Ladd Irvine, a marine mammal ecologist with Oregon State University in Newport. Two others were found dead in the same area, but the cause of death was inconclusive. This may not seem significant, but in a population of 2,500, five dead blue whales were enough for the National Oceanic and Atmospheric Administration (NOAA) to declare the deaths "unusual mortality events."
Irvine and colleagues hope the new satellite tracking data-funded in part by a National Geographic grant-can help modify existing shipping lanes to minimize run-ins between ships and whales. The study authors note that one of the southern California lanes, which runs between three of the Channel Islands and Santa Barbara, could be moved southward to avoid the whales' highest-use areas.
That would be difficult, says Michelle Berman-Kowalewski, a marine mammal biologist with the Channel Islands Cetacean Research Unit in Santa Barbara, California, who was not involved in the study. The U.S. Navy has testing sites in the area of the proposed new lane, so rerouting ship traffic would be a challenge.
Irvine acknowledges the difficulties, but says that NOAA is trying to bring shipping companies, the U.S. Navy, and other stakeholders together to work out the best routing of shipping lanes for everyone involved.
Source: National Geographic
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