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Recovery Strategy for Blue, Fin, and Sei Whales in Pacific Canadian Waters [Proposed]

5. Threats (cont'd)

5.2 Current threats

Ship strikes, chronic noise from shipping, and acute noise from low frequency active sonar and seismic exploration are potentially the greatest current threats to balaenopterid whales. Commercial shipping, oil and gas extraction, and seismic surveys, have the potential to reduce potential habitat for these species by making areas uninhabitable due to increased background noise levels, at least for short periods of time. Entanglement in fishing gear and marine debris may also pose threats to individuals. As populations increase, fin whales in particular may become more at risk to interactions with human activities because of their more coastal distribution. Pollution is an increasing concern in the oceans, though there is currently little evidence to suggest a significant impact on balaenopterids. However, synergistic effects of seemingly unrelated stressors have recently been identified in other mammal species and cannot be ruled out for cetaceans (Sih et al. 2004 cited in Payne 2004).

While threats are difficult to prioritize given the lack of information, ship strikes should currently be considered the most important threat to individual balaenopterids in Pacific Canadian waters, particularly fin whales because of their more coastal distribution. The possibility that habitat degradation (or loss of use), through increased background noise levels, may limit the recovery of these species near shipping lanes and other areas of high noise production should also be considered a leading threat.

5.2.1.  Ship strikes

Blue and fin whales often occupy shelf-break locations that frequently coincide with shipping lanes, which concentrate large vessel traffic. In a review of 292 records of ship strikes, Jensen and Silber (2004) reported that fin whales were the most commonly struck species, while blue and sei whales were two of the least likely to be struck. However, strikes of offshore species are more likely to go undetected. The mortality rate associated with ship strikes is 70-80% (Jensen and Silber 2004). In the St. Lawrence, 16% of observed blue whales have marks associated with large propellers or hulls (Sears and Calambokidis 2002). Between 1980 and 1993, at least four blue whales were struck and killed off California. An additional four injuries and two mortalities of large whales were attributed to ship strikes during 1997-2001 in North Pacific waters (Carretta et al. 2003). At least six fin whales were reported struck and killed in or near Pacific Canadian waters between 1999 and 2004 (COSEWIC 2004), and a single dead sei whale came into the Strait of Juan de Fuca on the bow of a ship in 2003. It appears that large vessels travelling more than 14 knots (26 km/h), particularly high-speed container ships, present the greatest risk of ship strike mortality to whales (Laist et al. 2001). Container and cruise ship traffic through British Columbia ports has increased by 200% since the 1980s (Canada 2005), and growth can be expected to continue.

More data on the distribution of blue, fin, and sei whales and the identification of how their critical habitat overlaps with shipping lanes will help determine the degree to which ship strikes threaten balaenopterid whales.