Risk assessment of vessel traffic on endangered blue and humpback whales in the Gulf of the Farallones and Cordell Bank National Marine Sanctuaries: Summary of research results

Publications >> Risk assessment of vessel traffic on endangered blue and humpback whales in the Gulf of the Farallones and Cordell Bank National Marine Sanctuaries: Summary of research results

Citation

Keiper, C., J. Calambokidis, G. Ford, J. Casey, C. Miller, and T. Kieckhefer. 2012. Risk assessment of vessel traffic on endangered blue and humpback whales in the Gulf of the Farallones and Cordell Bank National Marine Sanctuaries: Summary of research results. Report to Pacific Life Foundation.

Executive summary

The identification of cetacean habitat use associated with major feeding areas for endangered blue (Balaenoptera musculus) and humpback whales (Megaptera novaeangliae) within areas of high ship densities has become of greater conservation importance in the San Francisco Bay area due to the three endangered whales that died from ship strike injuries during July, September and October 2010. The objective of this study was to examine ship use in shipping lanes approaching San Francisco Bay in relation to temporal and spatial high use areas of blue and humpback whales to identify primary areas of overlap and assess potential risks. The study area extended from 35.5‐38.5 °N Latitude and from 121‐124°W Longitude and included Cordell Bank and Gulf of the Farallones National Marine Sanctuaries.

This study conducted by Oikonos Ecosystem Knowledge, Cascadia Research Collective, R.G. Ford Consulting Company, the Naval Post Graduate School Ocean Acoustics Laboratory, and Save The Whales was made possible through funding from Pacific Life Foundation.

To measure relative risk of impacts of vessel traffic and evaluate collision potentials to blue and humpback whales during seasonal foraging high use areas we did the following: 1) identified blue and humpback whale habitat use patterns; 2) identified vessel traffic patterns during Aug‐Oct 2009‐2010; and 3) identified overlap of humpback and blue whale distributions during seasonal high use feeding and transiting locations and vessel traffic densities near and in San Francisco shipping lanes. Aug‐Oct was selected because historically, both blue and humpback whales tend to be more abundant during these months in the study area when their preferred prey (krill and small schooling fish) are most abundant.

Results of humpback and blue whale habitat use patterns indicated greatest densities occurred near the continental shelf edge, along the inner side of the shelf edge and along the shelf slope, at Cordell Bank, and west, north and south of the Farallon Islands, and also on the continental shelf in the Gulf of the Farallones and Cordell Bank National Marine Sanctuaries. The observations made during whale watching cruises and other studies exhibited a similar pattern. Results of San Francisco approach vessel traffic patterns during Aug‐Oct 2009‐2010 indicated the greatest numbers of vessels were cargo ships (52%) and tankers (24%); 14% were ‘Other’ (passenger, pilot vessel, search and rescue, port tender, military ops, underwater ops, law enforcement, sailing, pleasure, fishing, unidentified); and 10% were towing or tugs. Overlap of whale density and vessel density results indicated the principal areas of relative risk were the western approach shipping lanes that intersect the shelf edge within the Gulf of the Farallones and in the Cordell Bank area where the (extended) north‐west lanes pass through the shelf north of the Gulf of the Farallones.

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