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West Coast whale deaths from ship collisions far higher than previously estimated- new Point Blue-led publication

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August 21, 2017

Rockwood RC, Calambokidis J, Jahncke J (2017) High mortality of blue, humpback and fin whales from modeling of vessel collisions on the U.S. West Coast suggests population impacts and insufficient protection. PLoS ONE 12(8): e0183052. https://doi.org/10.1371/journal.pone.0183052 [abstract below]

Paul Rogers/Mercury News Coverage: New study: West Coast ships kill more than 80 endangered whales annually

From the Point Blue press release:

Blue, humpback, and fin whale mortality from ship strikes in U.S. West Coast waters is far higher than current estimates based on carcasses washed ashore, according to a new study published this week in PLOS ONE by Point Blue Conservation Science (Point Blue) and collaborators at Cascadia Research Collective.

Point Blue scientists estimate that each year 18 blue, 22 humpback, and 43 fin whales die off the west coast from ship strikes from June-November, the peak feeding time.  These estimates far surpass the average numbers of whales per year that are found washed ashore as a result of collisions.

Shipping lanes were found to be some of the areas of greatest risk since they contain concentrated ship traffic and, in some cases, high-use whale habitat. Thus, intensified efforts to refine shipping lane placement and institute shipping lane speed reductions are high priorities.  However, the scientists also reported that the majority of whale strikes happen outside of the ship traffic lanes off California….

Despite the more extensive area of risk outside shipping lanes, most mortality is in a relatively confined area off Central and Southern California.  Point Blue found that 74% of blue whales mortality, 82% of humpback whale mortality and 65% of fin whale mortality fall within only 10% of the U.S. West Coast waters.  To decrease vessel collisions with whales, the scientists recommend expanding mitigation efforts in those areas off Central and Southern California, including expanding actions to slow ships down and safeguard key feeding areas outside of current shipping lanes….

Extensive harvest of whales during the twentieth century has left many populations severely depleted. Ship strikes are a primary cause of death for whales today and threaten the recovery of populations. Current mitigation efforts focus on the traffic lanes off San Francisco and Long Beach but whales killed by ships continue to wash ashore despite these voluntary speed reductions.  Most whales sink upon death, leaving no way for scientists to directly count the number of victims from ship strikes.

To circumvent this problem, the study authors used a modeling approach modified from naval warfare encounter theory to estimate mortality for blue, humpback and fin whales in West Coast waters out to 200 nautical miles offshore.

Point Blue found that shipping lanes did not represent the largest concentration of whale collisions. Only 13% (blue whale), 18% (humpback whale) and 3% (fin whale) of deaths occur in the delineated shipping lanes, which means that conservation efforts in these areas only could not sufficiently reduce ship strike mortality.

“Our work confirms that the problem of ship strikes is a significant concern for West Coast whales. The increases in deaths that we have been seeing in recent years means that establishing a regional approach to minimizing whale mortality from ship strikes is a critical next step,” says Cotton Rockwood, Senior Marine Ecologist at Point Blue and lead author.

The next phase of Point Blue’s research will test how to minimize ship strikes and reduce whale mortality by modifying shipping lanes, developing ship speed reductions guidelines for areas further offshore, and suggesting ‘areas to be avoided’ around whale feeding hotspots.

Publication Abstract:

Mortality from collisions with vessels is one of the main human causes of death for large whales. Ship strikes are rarely witnessed and the distribution of strike risk and estimates of mortality remain uncertain at best. We estimated ship strike mortality for blue humpback and fin whales in U.S. West Coast waters using a novel application of a naval encounter model. Mortality estimates from the model were far higher than current minimum estimates derived from stranding records and are closer to extrapolations adjusted for detection probabilities of dead whales. Our most conservative model estimated mortality to be 7.8x, 2.0x and 2.7x the U.S. recommended limit for blue, humpback and fin whales, respectively, suggesting that death from vessel collisions may be a significant impediment to population growth and recovery. Comparing across the study area, the majority of strike mortality occurs in waters off California, from Bodega Bay south and tends to be concentrated in a band approximately 24 Nm (44.5 km) offshore and in designated shipping lanes leading to and from major ports. While some mortality risk exists across nearly all West Coast waters, 74%, 82% and 65% of blue, humpback and fin whale mortality, respectively, occurs in just 10% of the study area, suggesting conservation efforts can be very effective if focused in these waters. Risk is highest in the shipping lanes off San Francisco and Long Beach, but only a fraction of total estimated mortality occurs in these proportionally small areas, making any conservation efforts exclusively within these areas insufficient to address overall strike mortality. We recommend combining shipping lane modifications and re-locations, ship speed reductions and creation of ‘Areas to be Avoided’ by vessels in ecologically important locations to address this significant source of whale mortality.

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