Potential impact of offshore human activities on gray whales

0,09

MB

7

stron

6604

ID

National Oceanic and Atmospheric Administration

2002

rok

ABSTRACT

Gray whale (Eschrichtius robustus) reactions to offshore human activities have been relatively well

studied compared to those of other mysticetes. Studies of short-term behavioural responses to

underwater noise associated with aircraft, ships and seismic explorations indicate a 0.5 probability

that whales will respond to continuous broadband noise when sound levels exceed ca 120dB2 and to

intermittent noise when levels exceed ca 170dB, usually by changing their swimming course to

avoid the source. Gray whales were ‘startled’ at the sudden onset of noise during playback studies,

but demonstrated a flexibility in swimming and calling behaviour that may allow them to circumvent

increased noise levels. Whales may be ‘harassed’ by noise from large commercial vessels,

especially in shipping lanes or near busy ports.

Gray whales sometimes change course and alter their swimming speed and respiratory patterns

when followed by whalewatching boats. Conversely, some whales swim toward small skiffs

deployed from whalewatching boats in breeding lagoons, seemingly attracted by the noise of idling

outboard engines. Reported gray whale reactions to aircraft are varied and seem related to ongoing

whale behaviour and aircraft altitude. Whale response to research involving tagging and biopsy

sampling appears to be short term. Gray whales were seen swimming through surface oil from the

Exxon Valdez oil spill along the Alaskan coast and showed only partial avoidance to natural oil seeps

off the California coast. Laboratory tests suggest that gray whale baleen, and possibly skin, may

be resistant to damage by oil, but spilled oil or oil dispersant in a primary feeding area could

negatively affect gray whales by contaminating benthic prey. Gray whales are sometimes injured

or killed in collisions with vessels or entanglement in fishing gear. Concern about the cumulative

long-term impact of offshore human activities is particularly acute in the Southern California Bight,

where many activities are often concurrent.