Abstract
The distribution and abundance of blue whales (Balaenoptera musculus) was assessed from ship surveys conducted in the Central and Northeast Atlantic in 1987, 1989, 1995 and 2001. Blue whales were most commonly sighted off western Iceland, and to a lesser extent northeast of Iceland. They were very rare or absent in the Northeast Atlantic. Sightings were combined over all surveys to estimate the detection function using standard line transect methodology, with the addition of a covariate to account for differences between surveys. Total abundance was highest in 1995 (979, 95% CI 137-2,542) and lowest in 1987 (222, 95% CI 115-440). Uncertainty in species identity had little effect on estimates of abundance. There was a significant positive trend in abundance northeast of Iceland and in the total survey area.
Highlights
Co-ordinated international North Atlantic Cetacean Sighting Surveys (NASS) were initiated in 1987 (Sigurjónsson et al 1989) and have been conducted 4 times (NASS-87, NASS-89, NASS-95 and NASS-2001)
Blue whales are relatively rare in the area surveyed by the NASS, and each individual survey produces too few sightings for reliable estimation of a detection function and abundance
It would be preferable to estimate the detection functions at the survey level, as the functional form of the detection function might vary between surveys, as has been observed with fin whales (Víkingsson et al 2009)
Summary
Co-ordinated international North Atlantic Cetacean Sighting Surveys (NASS) were initiated in 1987 (Sigurjónsson et al 1989) and have been conducted 4 times (NASS-87, NASS-89, NASS-95 and NASS-2001). In these surveys large areas of the northern North Atlantic have been covered simultaneously by up to 15 vessels and 2 aircraft with participation of up to five countries (reviewed in Víkingsson et al 2009). Blue whales (Balaenoptera musculus) have not been considered a primary target species of the NASS surveys, the coverage of the surveys is likely to have included a large part of the summer distribution area of the species in the northeast North Atlantic.
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