Distribution and Abundance of Killer Whales in the Central North Atlantic, 1987-2015

Daniel G Pike,Gísli Víkingsson,Geneviève Desportes,Bjarni Mikkelsen,Thorvaldur Gunnlaugsson

doi:10.7557/3.5579

Abstract

The North Atlantic Sightings Surveys (NASS), covering a large but variable portion of the Central and Eastern North Atlantic, were conducted in 1987, 1989, 1995, 2001, 2007 and 2015. Sightings of killer whales (Orcinus orca), a non-target species, were relatively rare in the Central Atlantic (Icelandic and Faroese) portions of the survey area. In cases where sighting numbers were insufficient, we pooled sightings over several surveys to derive a distance detection function and used this to estimate abundance using standard Distance Sampling methodology. Uncorrected estimates were produced for all surveys, and estimates corrected for perception bias were produced for the 2001 and 2015 surveys. Killer whales were sighted in all areas but were most common in the eastern part of the survey area. Uncorrected abundance in the NASS core area ranged from a low of 4,736 (95% CI: 1,842–12,176) in 1995 to a maximum of 15,142 (95% CI: 6,003–38,190) in 2001. The low precision of the estimates makes the detection of temporal trends unlikely. In 2007 an extension survey revealed relatively high numbers of killer whales to the east of the survey area, in conformity with Norwegian survey estimates in this area. The NASS and other surveys conducted over the period indicate that killer whales number in the low tens of thousands in the Central and Eastern North Atlantic.

Highlights

The North Atlantic Sightings Surveys (NASS) are a series of large scale ship-based and aerial cetacean line transect surveys conducted 6 times over the last 30 years, in 1987, 1989, 1995, 2001, 2007 and 2015 (Pike, 2009; Pike et al, 2020a; Pike, Gunnlaugsson, Sigurjónsson & Víkingsson, 2020b; Pike, Gunnlaugsson, Mikkelsen, Halldórsson & Víkingsson, 2019a; Pike et al, 2019b)
The surveys, organized under the supervision of the Scientific Committees of the North Atlantic Marine Mammal Commission (NAMMCO) and the International Whaling Commission (IWC), have had the primary objective of obtaining information on the distribution and abundance of cetaceans to be used in the management of direct and indirect anthropogenic takes of these animals
While there is no minimum number of detections necessary to derive a detection function model, other than the number of detections must exceed the number of model parameters, we considered 30 sightings as a minimum for a robust model

Summary

Introduction

The North Atlantic Sightings Surveys (NASS) are a series of large scale ship-based and aerial cetacean line transect surveys conducted 6 times over the last 30 years, in 1987, 1989, 1995, 2001, 2007 and 2015 (Pike, 2009; Pike et al, 2020a; Pike, Gunnlaugsson, Sigurjónsson & Víkingsson, 2020b; Pike, Gunnlaugsson, Mikkelsen, Halldórsson & Víkingsson, 2019a; Pike et al, 2019b). Target species of the surveys have been the common minke whale (Balaenoptera acutorostrata) in the Norwegian survey area, the common minke whale, fin whale (Balaenoptera physalus) and long-finned pilot whale (Globicephala melas) in the Icelandic and Faroese areas, and the common minke whale, fin whale and humpback whale (Megaptera novaeangliae) in Greenlandic areas. Estimates for these and several other species have been accepted by the Scientific Committees of NAMMCO and the IWC and published (NAMMCO, 2020; IWC, 2020)

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Discussion

Conclusion