After two dead fin whales were removed from the hull of the HMAS Sydney, an Australian destroyer conducting exercises off the coast of San Diego on May 8, U.S. Navy officials emphasized that the service takes protective measures to mitigate environmental risks, according to a statement to Military.com.
"Whenever the U.S. Navy trains and/or tests, it employs protective measures that have been developed in coordination with the NOAA Fisheries," a spokesman for U.S. Pacific Fleet told Military.com. "Those measures include using qualified lookouts; reducing power or halting active sonar transmissions when marine mammals get within a predetermined safety range; establishing safety zones around detonations; and maneuvering vessels to avoid marine mammals/endangered species."
The National Oceanic and Atmospheric Administration, an agency that shapes international ocean policy and addresses threats to natural resources, has taken several measures to prevent vessel strikes, including establishing speed restrictions and tracking vessel strikes through carcass examinations with the Marine Mammal Stranding Network.
Navy officials released a statement in the days immediately following the incident, saying, "The Navy takes marine mammal safety seriously and is disheartened this incident occurred."
In a letter last week, the Center for Biological Diversity announced its intent to sue the U.S. Navy and the National Marine Fisheries Service for what it called "violations" of the Endangered Species Act.
The incident is under joint review by U.S. and Australian agencies.
Five vessel strikes off the coast of California between 2018 and 2020 involved fin whales, according to federal data.
Though an analysis of data from the International Whaling Commission ship strike database indicates that approximately 239 marine mammals were hurt by vessel strikes in U.S. waters since 1820, research from NOAA suggests that marine mammal populations across the western coast, including California, are stable.
"Many marine mammal stocks in the West Coast Region are stable and/or increasing," research from NOAA's Marine Mammal Health and Stranding Response Program states.
Despite best efforts to mitigate environmental damage, vessel size and speed can contribute to inadvertent vessel strikes, according to NOAA.
"Marine animals can be difficult for a vessel operator to see because they are not always clearly visible from the surface," information on vessel strikes from NOAA states. "And even if the operator sees the animal clearly, there may be no time for either of them to avoid a collision.
The Navy attaches long-term satellite tags to fin whales to study their movement patterns and help reduce the risk of vessel strikes, according to information from the Hawaii-Southern California Training and Testing, or HSTT.
In addition to its own mitigation measures, the Navy utilizes the Early Warning System in various parts of the country to reduce ship strikes on whales, a study on vessel collisions reports.
Though mammal injury is possible when operating large ships, like the HMAS Sydney, research from HSTT indicates that the majority of incidents happen during training and testing activities and do not result in injury.
"Less than 0.03% of all estimated [incidents] would result in permanent threshold shifts or injury … or mortality," a 2017 HSTT environmental impact statement found.
It adds that temporary shifts in animal behavior -- including marine mammals acknowledging the sound, changing their vocalization and avoiding naval activity -- were the most common response, accounting for 99.97% of all interactions.
Available research indicates that "extremely high-risk" areas for marine mammals in North America "are attributable mainly to large commercial ships near major ports."
Analysis of 134 vessel strikes with a known vessel type in a NOAA technical memorandum found that Navy ships accounted for 17.1% of whale strikes; container/cargo ships/freighters, 14.9%; whale-watching vessels, 14.2%, cruise ships/liners, 12.7%, ferries, 11.9%; Coast Guard vessels, 6.7%; tankers, 6.0%; recreational vessels and steamships, 5.2%; fishing vessels, 3.0%; and other vessels, 0.75%.
However, the data may be somewhat skewed because Navy and Coast Guard vessels are required to report animal strikes, while other ships are not.
"Strikes of large whales by military vessels have been reported in U.S. and Canadian waters fairly often relative to other vessel types," the research found. "The data are skewed relative to other vessel types, however, because in the [U.S.], military vessels are required to report whale strikes as a condition of permitting certain naval exercises."