Abundance of Whales in West and East Greenland in Summer 2015

Rasmus S. Larsen,Nynne H. Nielsen,Mikkel H. S. Sinding,Rasmus D. Nielsen,Outi Tervo,Rikke Guldborg Hansen,Marianne H. Rasmussen,Mads Peter Heide-Jørgensen,Tenna K. Boye

doi:10.7557/3.4689

Rasmus S. Larsen, Nynne H. Nielsen + Show 7 more

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https://doi.org/10.7557/3.4689

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Abstract

An aerial line transect survey of whales in West and East Greenland was conducted in August-September 2015. The survey covered the area between the coast of West Greenland and offshore (up to 100 km) to the shelf break and in East Greenland from the coast up to 50 km offshore crossing the shelf break. A total of 423 sightings of 12 cetacean species were obtained and abundance estimates were developed for common minke whale, (Balaenoptera acutorostrata), fin whale (Balaenoptera physalus), humpback whale (Megaptera novaeangliae), harbour porpoise (Phocoena phocoena), long-finned pilot whale, (Globicephala melas) and white-beaked dolphin (Lagenorhynchus albirostri). The estimates were corrected for perception bias and availability bias where possible. Data on surface corrections for minke whales and harbour porpoises were collected from whales instrumented with satellite-linked time-depth-recorders. Options for estimation methods are presented and the preferred estimates are: minke whales: 5,095 (95% CI: 2,171-11,961) in West Greenland and 2,762 (95% CI: 1,160-6,574) in East Greenland, fin whales: 2,215 (95% CI: 1,017-4,823) in West Greenland and 6,440 (95% CI: 3,901-10,632) in East Greenland, humpback whales: 993 (95% CI: 434-2,272) in West Greenland and 4,223 (95% CI: 1,845-9,666) in East Greenland, harbour porpoises: 83,321 (95% CI: 43,377-160,047) in West Greenland and 1,642 (95% CI: 319-8,464) in East Greenland, pilot whales: 9,190 (95% CI: 3,635-23,234) in West Greenland and 258 (95% CI: 50-1,354) in East Greenland, white-beaked dolphins 15,261 (95% CI: 7,048-33,046) in West Greenland and 11,889 (95% CI: 4,710-30,008) in East Greenland. The abundance of cetaceans in coastal areas of East Greenland has not been estimated before, but the limited historical information indicates that the achieved abundance estimates were remarkably high. Comparing the estimates from 2015 in West Greenland with a similar survey conducted in 2007, there is a trend towards lower densities in 2015 for the baleen whale species and white-beaked dolphins. Harbour porpoises and pilot whales, however, did not show a similar decline. The decline in baleen whale and white-beaked dolphin abundance is likely due to emigration to the East Greenland shelf areas where recent climate driven changes in pelagic productivity may have accelerated favourable conditions for these species.

Highlights

Most cetacean species that occur in West Greenland are subject to various levels of subsistence hunting, which requires frequent abundance estimates for assessing the effects of the exploitation
This study presents results from an aerial line transect survey of small and large cetaceans in East and West Greenland conducted in August and September 2015
The average time spent at all 7 sampled depth bins for minke whales shows that the largest proportion of each hour was spent at depths >5 m and relatively small fractions of time were spent at the surface (Table 1)

Summary

Introduction

Most cetacean species that occur in West Greenland are subject to various levels of subsistence hunting, which requires frequent abundance estimates for assessing the effects of the exploitation. For a description of the survey platform setup see Heide-Jørgensen, Witting, Laidre, Hansen & Rasmussen et al (2010) As described by these authors, the first two surveys in 1984 and 1985 were conducted with the intention of obtaining uncorrected line transect estimates of the abundance of common minke whales, (Balaenoptera acutorostrata) (in the remainder of the article referred to as minke whales) and fin whales (Balaenoptera physalus), too few sightings were obtaifned to generate estimates. A cue-counting estimate of 10,792 (CV=0.59) minke whales corrected for whales missed by the observers (perception bias) was obtained based on a survey conducted in 2005 (Heide-Jørgensen et al, 2008) and a survey in 2007 resulted in a fully corrected estimate of 16,609 (CV=0.41) minke whales (Heide-Jørgensen, Witting, et al, 2010)

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