Abundance and Distribution of Fin and Humpback Whales at the South Orkney Islands 2011–2025

Summary

This 15-year study reveals the South Orkney Islands as a critical feeding area for fin whales during Antarctic summer, with populations showing significant recovery. Fin whale densities increased dramatically from 2011-2025, reaching peak abundances of over 18,000 individuals in some years. The research demonstrates that both fin and humpback whales concentrate along the northern shelf break where krill density is highest, creating potential competition with commercial krill fishing operations. Current whale populations consume 4-8 times more krill daily than the commercial fishery harvests, highlighting the need for ecosystem-based fishery management.

Key Findings

Fin whale summer abundance ranged from 648 to 18,083 individuals across survey years

Significant increasing trend in fin whale density (0.02 ind./km² per year, P=0.03) suggesting population recovery

Both species concentrate along northern shelf break where krill density is highest

Fin whales consume 4,043-7,605 tons of krill daily - 4-8 times the average commercial catch rate

Humpback whales showed high variability with some years showing zero detections

Strong spatial overlap between whale feeding areas and commercial krill fishing grounds

Abstract

Information on cetacean population status is vital for determining fisheries management strategies, especially where they overlap spatiotemporally and target the same organism. This study aims to quantify distribution and abundance of fin (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) near the South Orkney Islands, an area in the Southern Ocean with the highest catches of Antarctic krill (Euphausia superba). Ship-based observational data were collected during the austral summers from 2011 to 2025. Most fin whale sightings were over the northern shelf-break and deeper offshore regions, with an annual density between 0.01 and 0.29 individuals per km⁻² (corresponding to a summer abundance range of 648–18,083 individuals). Humpback whales were mainly sighted north of the islands but more on-shelf, with annual densities between 0 and 0.07 individuals per km⁻² (average 590 individuals, with a summer abundance range of 0–4486 individuals). Summer abundances varied substantially, with fin whales increasing significantly (0.02 individuals per km⁻² per year, P-value 0.03), while no monotonic increase was detected for humpback whales.

Published in

ICES Journal of Marine Science

2025

Authors

Bjørn A. Krafft, Sebastian Menze, Georg Skaret, Ludvig A. Krag, Martin Biuw, Ulf Lindstrøm, Phil Trathan, Leif Nøttestad, Heidi Ahonen, Nat Kelly, Andrew Lowther

Institutions

Institute of Marine Research, Norway National Institute of Aquatic Resources, Technical University of Denmark Norwegian Polar Institute British Antarctic SurveyAustralian Antarctic Division

Methods

AcousticBiological sampling DataField

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