Distribution and abundance of in whales (Balaenoptera physalus) in the Northeast and Central Atlantic as inferred from the North Atlantic Sightings Surveys 1987-2001

North Atlantic Sightings Surveys (NASS) is a series of large scale international cetacean line transect
surveys, conducted in 1987, 1989, 1995 and 2001, that covered a large part of the central and eastern
North Atlantic. Target species were in (Balaenoptera physalus), common minke (B. acutorostrata),
pilot (Globicephala melas) and sei (B. borealis) whales. Here we present new estimates of abundance
for in whales from the 2 most recent surveys and analysis of trends throughout the survey
period. Fin whales were found in highest densities in the Irminger Sea between Iceland and Greenland.
Abundance of in whales in the survey area of the Icelandic and Faroese vessels (Central North
Atlantic) was estimated as 19,672 (95% C.I. 12,083-28,986) animals in 1995 and 24,887 (95% C.I.
18,186-30,214) in 2001. The estimates are negatively biased because of whales diving during the
passage of vessels, and whales being missed by observers, but these and other potential biases are
likely small for this species. The abundance of in whales increased signiicantly over the survey
period. For all areas combined the estimated annual growth rate was 4%. An estimated annual increase
of 10% in the area between Iceland and Greenland was responsible for most of this overall
increase in numbers of in whales in the area. Although high, the estimated rates of increase are not
out of bounds of biological plausibility and can thus be viewed as recovery of a depleted population.
However, the apparent pattern of population growth and the whaling history in the area indicate that
in whales made a signiicant recovery during the irst half of the 20th century and that the recent
observed high growth rates cannot be explained solely by recovery after overexploitation.