Association Between Blue Whale (<I>Balaenoptera musculus</I>) Mortality and Ship Strikes Along the California Coast

Abstract

Blue whales (Balaenoptera musculus) are distributed worldwide, and although severely depleted by commercial whaling, their abundance off the California coast now appears to be increasing. Little is known about natural causes of mortality of blue whales, but human-related mortality continues despite legal protection. Ship strikes are a significant mortality factor for other species of baleen whale, and changes in shipping traffic have been advocated to minimize further deaths. Between 1988 and 2007, 21 blue whale deaths were reported along the California coast, typically one or two cases annually. Three pulses in strandings were observed, with three carcasses observed in fall 1988, three in 2002, and four in fall 2007. Two of the four animals in 2007 were first observed dead in the Santa Barbara Channel and had wounds typical of a ship strike. Blue whale strandings were spatially associated with locations of shipping lanes, especially those associated with the Ports of Los Angeles and Long Beach, and were most common in the fall months.

Criteria and case definitions for serious injury and death of pinnipeds and cetaceans caused by anthropogenic trauma

“…40). Age biases appear to exist with respect to likelihood of ship strike, with juveniles showing a greater tendency to be struck (Wiley et al 1995, Hamilton et al 1998, Knowlton & Kraus 2001, Laist et al 2001, Panigada et al 2006, Lammers et al 2007, Douglas et al 2008, Berman-Kowalewski et al 2010, Carrillo & Ritter 2010, Neilson et al 2012. Biases related to recovery rates of perinates/juveniles are not known.…”

“…Expansion of the body cavity by the uterus containing the fetus, fetal membranes, and fluids was thought to have resulted in increased abdominal pressure and stretching of the abdomen resulting in structural tension greater than the tensile strength of the scarred propeller wounds. Catalog: NEAq Eg #2143 'Lucky'; photo: UNCW ever vessels and animals are in close spatial and temporal proximity, as is seen in areas of high vessel traffic, particularly along the continental shelf (Fonnesbeck et al 2008, Berman-Kowalewski et al 2010. Propeller wounds have been observed in an array of small and large cetaceans, ranging from coastal delphinids to mysticetes (Wells & Scott 1997, Van Waerebeek et al 2007, Wells et al 2008, as well as sea otters and a number of pinnipeds (Goldstein et al 1999, Kreuder et al 2003.…”

“…Propeller injuries have been observed during all months of the year; however, specific temporal and spatial exceptions may occur in some species, particularly when feeding or breeding ranges intersect with shipping routes or boating channels (e.g. blue whales and NARW) (Fonnesbeck et al 2008, Berman-Kowalewski et al 2010. In some cases (M. J. Moore unpubl.…”

Seasonal distribution and abundance of cetaceans off Southern California estimated from CalCOFI cruise data from 2004 to 2008

“…Although these waters are important to marine fauna, they are also increasingly important to humans who use them for commercial shipping and fishing; oil and gas exploration, development, and production; naval exercises; and recreation. The combined use of these highly productive waters by cetaceans and humans can lead to ships striking large whales (Jensen and Silber, 2003;Berman-Kowalewski et al, 2010), entanglements of cetaceans in fishing gear (Julian and Beeson, 1998;Laist et al, 2001;Carretta et al, 2011b), and disruption of normal behaviors by underwater sound (McDonald et al, 2006;Weilgart, 2007). To assess long-term impacts of fisheries, industry, and ecosystem variability on marine mammals, it is necessary to estimate abundance, understand stock structure, and determine seasonal habitat use by the species that inhabit these waters.…”

Do ship strikes threaten the recovery of endangered eastern North Pacific blue whales?

“…Although the magnitude of ship strikes is uncertain, it is likely above the legal "Potential Biological Removal" (PBR) level of 3.1 whales per year (Carretta et al 2012, Redfern et al 2013. This has led to speculation that ship strikes may be limiting the growth of the ENP population and calls for further research into potential approaches for mitigation (Berman-Kowalewski et al 2010, Redfern et al 2013.…”