Estimated Abundances of Cetacean Species in the Northeast Atlantic from Two Multiyear Surveys Conducted by Norwegian Vessels between 2002–2013

Nils Øien,Deanna Leonard

doi:10.7557/3.4695

Nils Øien, Deanna Leonard

Open Access

https://doi.org/10.7557/3.4695

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Abstract

Two shipboard line-transect surveys of the Northeast Atlantic were conducted between 2002–2007 and 2008–2013 to meet the ongoing requirements of the Revised Management Procedure (RMP) for common minke whales (Balaenoptera acutorostrata acutorostrata) developed by the International Whaling Commission’s Scientific Committee. Here we present estimated abundances for non-target species for which there were sufficient sightings, including fin whales (Balaenoptera physalus), humpback whales (Megaptera novaeangliae), sperm whales (Physeter macrocephalus), killer whales (Orcinus orca), harbour porpoises (Phocoena phocoena), and dolphins of genus Lagenorhynchus. The 2 surveys were conducted using a multiyear mosaic survey design with 2 independent observer platforms operating in passing mode, each with 2 observers. The abundances of Lagenorhynchus spp. from the 2002–2007 survey were estimated using single-platform standard distance sampling methods because of uncertainty in identifying duplicate sightings. All other estimates were derived using mark-recapture distance sampling techniques applied to a combined-platform dataset of observations, correcting for perception bias. Most notably, we find that the abundance of humpback whales, similar in both survey periods, has doubled since the 1990s with the most striking changes occurring in the Barents Sea. We also show that the pattern in distribution and abundance of fin whales and sperm whales is consistent with our earlier surveys, and that abundances of small odontocete species, which were not estimated in earlier surveys, show stable distributions with some variation in their estimates. Our estimates do not account for distributional shifts between years or correct for biases due to availability or responsive movement.

Highlights

Two multi-year surveys, targeting North Atlantic common minke whales (Balaenoptera acutorostrata acutorostrata), were conducted in the Northeast Atlantic between 2002–2007 and 2008–2013
Given that SVI accounted for only 2% of the total sightings in the previous survey period (Øien, 2009), the lack of effort in this area is not expected to have had a large effect on total abundance
The EW4 block was not covered in the 2002–2007 survey, nor in the earlier 1996– 2001 and 1995 surveys because it was not included as part of the Small Management Areas (SMA) under the minke whale Revised Management Procedure (RMP) until 2003 (Øien, 2009; IWC, 2004)

Summary

Introduction

Two multi-year surveys, targeting North Atlantic common minke whales (Balaenoptera acutorostrata acutorostrata), were conducted in the Northeast Atlantic between 2002–2007 and 2008–2013. A cyclical mosaic survey design was implemented in 1996 to cover the Northeast Atlantic with a patchwork of smaller-scale surveys over a multi-year timeframe (Øien & Schweder, 1996). These are the second and third complete surveys under the mosaic survey design. The survey methodology has remained essentially the same, with slight improvements to ensure best possible estimates of minke whale abundance as the target species (Schweder, Skaug, Dimakos, Langaas, & Øien, 1997; Skaug, Øien, Schweder, & Bøthun, 2004)

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