Distribution and abundance of large whales in Norwegian and adjacent waters based on ship surveys 1995-2001

Nils Øien

doi:10.7557/3.2704

Abstract

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.

Highlights

Shipboard sightings surveys with minke whales (Balaenoptera acutorostrata) as the target species have been conducted in Norwegian and adjacent waters as part of management needs, and as contributions towards the synoptically conducted NASS (North Atlantic Sightings Surveys) surveys, during the summer seasons around July in each of the years 1987, 1989 and in 1995 (Schweder et al 1997)
This is a specific adaptation of sightings procedures to the estimation method that we have implemented for minke whales (Skaug et al 2004) but this implies that the data collection may not be optimal for other species sighted during these surveys
One specific concern is about large whale sightings, which usually are seen at much larger distances than minke whales and smaller cetacean species for which detection cues usually are parts of the body in our waters

Summary

Introduction

Shipboard sightings surveys with minke whales (Balaenoptera acutorostrata) as the target species have been conducted in Norwegian and adjacent waters as part of management needs, and as contributions towards the synoptically conducted NASS (North Atlantic Sightings Surveys) surveys, during the summer seasons around July in each of the years 1987, 1989 and in 1995 (Schweder et al 1997). In 1996-2001 a 6 year programme was conducted to survey the northeast Atlantic with smaller effort annually (Øien and Schweder MS 1996). Minke whales are the primary survey target, sightings of other whale species were recorded, and large whale abundance estimates were published for the earlier surveys in 1988 and 1989 (Øien 1990, Christensen et al 1992a). Large whales have in this paper been used as a common term for fin (B. physalus), sei (B. borealis), blue (B. musculus), humpback (Megaptera novaeangliae) and sperm whales (Physeter macrocephalus)

Methods

Results

Conclusion