Vessel Strikes

whale tail and large ship on the ocean
A blue whale surfaces in close proximity to a large container ship. John Calambokidis, Cascadia Research

Whale deaths from vessel collisions, or ship strikes, are a significant challenge to whale conservation worldwide. Fatal strikes on whales, including endangered species, is an ongoing issue (2007-2020 confirmed ship strike data summary). Documented ship strike deaths and serious injuries are derived from observed whale carcasses and are considered minimum values. Studies indicate this is likely a small percentage of actual mortality. A comparison of average annual vessel strikes observed over the period 2013 to 2017 versus estimated vessel strikes indicates that the rate of reporting for whale vessel strikes is approximately 10% for humpback whales and 2% for blue whales (2019 NMFS Stock Assessment Report). The impact of ship strikes on the West Coast blue whale population is a significant concern, given their reduced population estimate, their low reproduction rate, and vulnerability to ship strikes compared with other species. Other whales are also at risk, including endangered and threatened humpback and fin whales.

San Francisco Bay ports are major maritime commerce hubs for international trade on the West Coast, contributing significantly to the region's economic base and bringing food and goods to the Bay Area's nearly eight million people. Transversed by ships coming into and out of port, these waters are federally protected as Monterey Bay, Greater Farallones and Cordell Bank national marine sanctuaries. The sanctuaries are destination feeding areas for threatened and endangered humpback and blue whales from late spring through the fall. The whales migrate annually to Greater Farallones to feed on krill and shoals of schooling anchovies, sardines, and herring. The co-occurrence of ships and whales creates a high likelihood that ships moving in and out of San Francisco Bay in the traffic lanes will transit through aggregations of feeding whales. For example, in June 2020, a single aggregation of at least 47 blue whales was documented just 28 miles west of the Golden Gate, adjacent to busy shipping lanes.

Taking Action to Protect Whales

Cover of VESSEL STRIKES AND ACOUSTIC IMPACTS report
Sanctuary Advisory Councils' VESSEL STRIKES AND ACOUSTIC IMPACTS

In 2011, Cordell Bank and Greater Farallones national marine sanctuaries launched an initiative to reduce vessel strikes and acoustic impacts. A joint working group of these sanctuaries' advisory councils was formed to bring people together with expertise in marine mammal science, ocean acoustics, commercial shipping, and conservation. The working group considered ship strikes and ocean noise and made recommendations to the advisory councils on how sanctuaries could address these issues. The sanctuary advisory councils discussed and forwarded recommendations to the sanctuaries.