The risk of ship strikes to endangered whales off the coast of Southern California, including Malibu, is the focus of a new study released this month.
The study, "Assessing the Risk of Ships Striking Large Whales in Marine Spatial Planning," was published in the most recent issue of the scientific journal Conservation Biology.
The study area, which is primarily used for shipping, military training and fishing, stretches from Point Conception to Long Beach.
Whales known off Southern California's coast include the humpback, blue and fin whales. All three species are listed as endangered under the U.S. Endangered Species Act. Of the three, blue and fin whales were more commonly sighted off Malibu's coast.
"We know several endangered species of whales occur in the waters off Southern California," Jessica Redfern, a NOAA Fisheries marine mammal biologist and lead author of the paper, told Science Daily. "What we didn't know, and what this study helps provide, is an understanding of the areas with the highest numbers of whales."
Ship strikes of blue whales have been documented for 20 years off Southern California, but the issue gained more attention in 2007 when four blue whales were killed by ships.
Most recently, a fin whale washed ashore at Little Dume in Malibu. A necropsy by the California Wildlife Center determined the young whale died from a ship strike.
Researchers used whale sightings and oceanographic data collected by the National Marine Fisheries Service's Southwest Fisheries Science Center from 1991 to 2009.
Using models, researchers showed the potential conflict between shipping and military uses with the whales.
Humpback whales had the most predictable route in the northern area of the study area, near Santa Barbara and the Channel Islands. Blue and fin whales were found throughout the study area.
The shipping lanes studied included:
- The shipping route in the Santa Barbara Channel, which is the current shipping route;
- A Central route south of the northern Channel Islands;
- A Central Fan route, or just the eastern part of the Central route; and
- A Southern route, a course south of the Central route and constrained by the protected areas around Santa Barbara, Santa Catalina, and San Nicolas Islands.
The study found that the Santa Barbara Channel Route, which passes through the National Marine Sanctuary and other marine protected areas, posed the greatest risk to humpback whales for ship strikes.
The Southern Route, which stays far out to sea beyond the Channel Islands, was the safest for the humpback whales, but had the highest risk for fin whales. The least amount of risk for the humpback and fin whales may be in the central routes, according to the study.
However, the blue whales, which were found throughout the study area, were at equal risk in all the routes.
On average, 5.9 humpback whales, 10.6 blue whales and 7.1 fin whales were struck by ships each year. The total number was difficult to assess because ship strikes are not widely reported or detected, according to the study.
The average number of blue whales killed exceeds standards set by the Marine Mammal Protection Act to ensure sustainable populations, the study states.