Ships Kill Endangered Blue Whales
Shipping Channel Deaths Emphasize Threats to World’s Largest Whales
Oct 17, 2007
The loss of three endangered blue whales (Balaenoptera musculus) in one month in the waters off of southern California prompted an unusual mortality event investigation. After ruling out ocean noise and harmful algal blooms, it was determined that ship strike was the sole cause of death for these blue whales. Large amounts of krill brought the whales into the area. Speed limits for boats and changes to the shipping lanes might prevent further deaths.
The Role of Krill in the Deaths
The blue whale , not only the largest whale but the largest animal in the world, feeds exclusively on krill, one of the smallest animals. This year the krill has been particularly abundant in southern California, which is also home to a quarter of the world’s blue whale population from June through November. And the krill has been staying close to the surface, bringing the blue whales into the path of the huge ships that travel through the area.
Other Potential Contributing Factors
Because there has never been a cluster of blue whale deaths like this, the National Marine Fisheries Service instituted an unusual mortality event investigation. In the past, Harmful Algal Blooms (HABs) in this area have resulted in large numbers of marine wildlife losses from domoic acid poisoning, so it was important to ensure that an HAB wasn’t occurring.
The investigators also looked for evidence of damage from recent naval sonar testing. In previous incidents where marine mammal mass strandings occurred within a short time of underwater mid-range sonar tests, the cetaceans that died were found to have hemorrhaging in the inner ear and some cranial spaces. This was not found in these animals, eliminating ocean noise as a contributing factor in the blue whale deaths.
All three blue whales were declared victims of ship strikes. The Santa Barbara Channel has a voluntary speed limit of 12 knots but very few ships travel this slowly, some going as fast as 30 knots. Researchers had counted more than 150 whales feeding in the area making the likelihood of collision fairly high. There has been some discussion of enforced speed limits or changes to the shipping lanes but no action has been taken.
Ship Speed Limits and Shipping Lane Alterations
Alterations have been made in shipping channels in the Atlantic off the US and Canadian coasts in an effort to protect the critically endangered right whale. In the Bay of Fundy the changes have separated important whale feeding grounds from shipping lanes, leaving the right whales, blue whales, and other marine wildlife largely undisturbed. Enforcement of reduced speed limits when right whales are present along various sections of their migratory route appear to be helping as well.
Whether similar changes will be instituted in the Pacific remains to be seen. Given that approximately 3000 blue whales come to the area to feed and that changes have worked in other areas for other whales, it seems a logical step. But with multiple agencies involved and pressure from the shipping industry to maintain the status quo, it may not happen. Several conservation organizations are keeping the issue in the fore in hopes of preventing further deaths. Having come back from near extinction by the whaling industry it would be a shame for the blue whale to be lost simply by a lack of action.
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