Distribution and abundance of large whales in Norwegian and adjacent waters based on ship surveys 1995-2001
2009
Øien, Nils
The abundances of large whale species are presented for the northeast Atlantic from near-complete survey coverage in 1995 and from multiple partial-area surveys during 1996-2001. These Norwegian shipboard surveys were generally conducted with 2 independent observer platforms, except for single-platform surveys during part of 1995. Tracking procedures implemented for minke whales – Balaenoptera acutorostrata (the target species) meant that the surveys had to be conducted in passing mode, and there were therefore only limited opportunities for closing on sightings to determine species identity and school size. Abundance estimates for large whale species (fin – Balaenoptera physalus, humpback – Megaptera novaeangliae and sperm whales – Physeter macrocephalus) were obtained by combining sightings from both platforms, and applying standard distance sampling techniques to the smeared and truncated perpendicular distances for each species. Abundance estimates for the 2 survey groupings (1995 and 1996-2001) summarised over comparable areas were: fin whales, 5,034 (cv 0.209) and 6,409 (cv 0.18); humpback whales, 1,059 (cv 0.248) and 1,450 (cv 0.29); and sperm whales, 4,319 (cv 0.199) and 6,207 (cv 0.22). The estimated cv’s are likely underestimates and specifically the combined partial-area survey cv’s do not include additional variance due to possible distributional shifts between years. Inclusion of a new survey stratum north of Iceland (block NVS) in the later set of surveys revealed a high additional abundance there of fin whales 3,960 (cv 0.538) and humpback whales 3,246 (cv 0.512). The high humpback whale estimate for this stratum confirms the Icelandic survey findings of a large humpback whale population summering in that area.
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