AERIAL DIGITAL PHOTOGRAPHIC SURVEYS OF NARWHALS, MONODON MONOCEROS, IN NORTHWEST GREENLAND

Narwhal ( Monodon monoceros ) abundance in Inglefield Bredning and adjacent fjords in Northwest Greenland was estimated using aerial digital photographic techniques in August 2001 and 2002. Two digital, large-format cameras continuously downloaded images to two laptop computers together with information on position, altitude, pitch, and roll of the aircraft. In 2001 a total of 11,628 images were obtained corresponding to a swept area of 840 km². The survey of the entire area was repeated four times and produced a count of 360 narwhals on the images or an average abundance in the surveyed area of 873 narwhals (CV = 0.35) at the surface. In 2002 the area was surveyed seven times and approximately 11,402 images were obtained. This corresponded to a swept area of 2,208 km² with 566 narwhals counted on the images, and an average estimated abundance of 562 narwhals (CV = 0.24) at the surface. Correcting these figures for availability bias (assuming narwhals are submerged deeper than 2 m for 62% of the time) results in abundance estimates of 2,297 (95% CI: 1,472–3,122) in August 2001 and 1,478 (95% CI 1,164–1,793) in August 2002. The uncorrected estimates, when compared to the results of visual line-transect surveys conducted in 1985 and 1986 (Born et al. 1994), show a 10% decline in recent years in the abundance of whales visible at the surface.