Research Objectives:
The antarctic blue whale population is so low that it is virtually impossible to obtain statistically significant encounter rates for population estimation during visual surveys. Unlike the large call repertoires of most bird species, blue whales within a given geographic area appear to have only one fundamental call type that is retained over many decades. The acoustic character of these calls is likely to become an important parameter in the revision of estimates of blue whale stocks and subspecies. Passive acoustic surveys document this variablility while visual surveys obtain such subspecies and stock information only when a biopsy can be obtained—which is rarely the case. The low frequency calls of blue (B. musculus) and fin (B.physalus) whales can be readily recorded out to a 20 kilometer radius providing more contacts in one-year than would be possible from even an extensive visual survey. Passive detection of whale calls provides a non-invasive and cost-effective means to sample mysticete populations year around in the Antarctic.
Technological advances in seafloor acoustic recorders have resulted in highly reliable, relatively low-cost, off-the-shelf, practical instruments while advances in our understanding of mysticete whale calling behavior have made acoustic estimation of population densities possible. These and other researchers continue to study mysticete whale call behavior in more accessible areas such as California coastal waters but some of the most important questions in mysticete whale population estimates lie in the Antarctic where the populations were most affected by harvesting.
This project will determine minimum population estimates, distribution and seasonality for mysticete whales, especially blue whales within the West Antarctic Peninsula region. Whales will be censused and monitored by detecting their calls on eight passive acoustic recorders deployed on the seafloor for a period of 15 to 18 months.
The deployment of a large aperture autonomous hydrophone array in the Antarctic will promote incorporation of passive acoustics as a tool for mysticete whale detection and census. Added to the suite of tools available for marine mammal detection, this method promises to provide new insight to the role of these top predators in the short food chains common to polar ecosystems. Moreover, the recovery or potential loss of the antarctic blue whale population that once numbered greater than 200,000 animals is not only a question of species extinction, but is relevant to all Southern Ocean ecosystem studies.
