Most whales sink when they die, disappearing without leaving researchers a clue as to the cause of their death. But a study published last week by Point Blue found that the number of whales dying in West Coast waters due to ship strikes is far greater than scientists previously estimated.
Using a new naval encounter model and focusing on three species, the study identified the exact locations and probabilities of fatal ship strikes—which are the number one cause of death for blue and fin whales and the second for humpback whales in the coastal region.
“Shipping moves 90 percent of the world’s commerce, and it’s an industry that’s only growing,” Cotton Rockwood, a marine ecologist and the senior author of the study, said. “We are not suggesting that we need to stop all shipping or even eliminate the occurrence of ship strikes, but we certainly need to understand this problem better. If the strikes are as high as our model predicts and shipping continues to increase, there’s a chance it could lead to declines.”
Point Blue scientists found that each year, 18 blue, 22 humpback and 43 fin whales die off the West Coast from strikes during peak feeding time, from June to November. Those numbers are far greater than the average number of whales found washed ashore as the result of collisions.
They are also far above the maximum numbers that the National Marine Fisheries Service says can die of unnatural causes without impacting their optimal population sizes. The so-called potential biological removal numbers are 2.3 individuals for blue whales, 11 for humpbacks and 16 for fin whales.
Researchers also discovered that although shipping lanes are the areas of greatest risk for the three species, the majority of strikes happen outside of those lanes. “We did not have that data before, and it means that we can’t just focus on shipping lanes to mitigate whale deaths. This data shows that efforts have to be much more comprehensive,” Mr. Rockwood said.
Five or six years ago, the Cordell Bank and Greater Farallones National Marine Sanctuaries spearheaded efforts to alter shipping routes based on known whale habitat and to establish voluntary speed reductions in and out of San Francisco Bay.
Between May and November, through published and broadcast notices to mariners, NOAA asks vessels of a certain size—300 gross tons or larger—to slow down. By reducing speed to 10 knots from the usual 15 or 20 knots, whale mortality rates go down significantly—even when an individual is hit.
In 2016, 27 percent of the shipping companies the sanctuaries contacted were cooperating, up from 18 percent the year before. “And this year, we are experimenting with monetary incentives,” Maria Brown, superintendent of the Greater Farallones Marine Sanctuary, said. A ship can receive $250 for slowing down as it transits between Long Beach and San Francisco and $1,000 when approaching or leaving each port for a maximum total of $2,500, she said.
“Yet there’s still room for protective action to be taken on the part of managers and of industry,” said John Calambokidis, a research biologist with Cascadia Research Collective, which collaborated on the study. Dr. Calambokidis began documenting blue whale behaviors and populations in the Greater Farallones in 1986 and then expanded his efforts across the entire West Coast.
Thanks to Cascadia Research’s photo database, over 3,000 blue whales in California can be identified just by distinguishing markings. One of those photographs identified the blue whale that washed up on Agate beach in Bolinas three months ago, based on distinguishing markings on her fluke. The female was first identified off California in 1999 and was subsequently seen in 11 different years, mostly in the Santa Barbara channel.
“By tracking these whales over so much time, you start not just seeing the larger issue of ship strikes, but rather individuals that you have encountered on many different occasions. There’s a more personal connection,” Dr. Calambokidis said. He added that the Point Blue study was much more comprehensive than anything attempted previously in the West Coast.
The model developed for the study had three essential parts—encounter risk, strike risk and mortality estimation—and each part was predicated on the previous part. Though Point Blue’s past marine research has related primarily to the areas within the two local marine sanctuaries, this study included waters offshore from California, Oregon and Washington.
Researchers used a combination of databases from multiple sources. To calculate spatial patterns of ship speed, draft, count and track distance, they used automatic identification system data from the Bureau of Ocean Energy Management and NOAA. For whale data, they used habitat density models developed by NOAA that demonstrate the distribution and concentration of whale populations.
Within the most biologically signifigant marine areas that were studied, they found that ship strikes have the greatest impact on humpbacks from the Greater Farallones to Monterey Bay, while the greatest strike risk for blue whales is between Santa Monica Bay and Long Beach. Fin whales tend to be less concentrated and swim the waters that are further offshore. The report noted that fin whales may present challenges in balancing mitigation strategies with the other two species because shifting vessel traffic could elevate fin whale strike risk.
While more specific priority areas exist for each species, a portion of the studied area has a high mortality rate for all three: the vast majority of whale deaths fall within certain areas of Central and Southern California. Focusing on avoiding these areas in particular could be a good first step in reducing strikes for all the species.
Now, Point Blue plans to test how to minimize ship strikes and reduce whale mortality by modifying shipping lanes, developing shipping reduction guidelines for areas further offshore and suggesting areas to be avoided around feeding hotspots. It will also study the impact of the speed reductions within the next year.