Aerial digital photographic surveys of narwhals, Monodon monoceros, in Northwest Greenland

Narwhal (Monodon monoceros) abundance in Inglefield Bredning and adjacent fiords 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 km. 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 km 2 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 (9590 Cl: 1,472-3,122) in August 2001 and 1,478 (9517b Cl 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.