Intra-season variations in distribution and abundance of humpback whales in the West Antarctic Peninsula using cruise vessels as opportunistic platforms

Summary

This study used tourist cruise ships as research platforms to track humpback whale numbers and locations in the Western Antarctic Peninsula during the 2019/2020 summer season. The findings show whale numbers increased rapidly through December, then leveled off by mid-January, with the whales moving from the northern Gerlache Strait to concentrate in the central Gerlache and southern Bransfield Straits. Researchers estimated peak whale numbers at 19,107 individuals (an increase from about 7,000 in 2000), with projected krill consumption between 1.4-3.7 million tons. The study found little overlap in time and space between whales and commercial krill fishing during November-January, though interactions could occur later in the feeding season.

This figure shows the timing of humpback whale presence versus krill fishing activity in the Western Antarctic Peninsula. The data reveals clear temporal separation between whale and fishery activities. Humpback whales are most abundant December through March, with peak consumption in January-February. Krill fishing occurs primarily April through July. The minimal overlap during the study period (November-January) confirms limited direct competition for krill resources in early summer, though potential interactions could occur later when both activities may coincide.

Key Findings

Humpback whale populations have recovered dramatically since 2000 (from ~7,000 to 19,107 individuals)

Whales consume an estimated 1.4-3.7 million tons of krill during their feeding season

Whale numbers increase rapidly through December, then stabilize by mid-January

Whales shift their distribution from northern Gerlache Strait to central Gerlache and southern Bransfield Straits during the season

Minimal overlap between whale feeding areas and commercial krill fishing during early summer (November-January) Illustration

Abstract

Fine-scale knowledge of spatiotemporal dynamics in cetacean distribution and abundance throughout the Western Antarctic Peninsula (WAP) is sparse yet essential for effective ecosystem-based management (EBM). Cruise vessels were used as platforms of opportunity to collect data on the distribution and abundance of humpback whales (Megaptera novaeangliae) during the austral summer of 2019/2020 in a region that is also important for the Antarctic krill (Euphausia superba) fishery, to assess potential spatiotemporal interactions for future use in EBM. Data were analyzed using traditional design-based line transect methodology and spatial density surface hurdle models fitted using a set of physical environmental covariates to estimate the abundance and distribution of whales in the area, and to describe their temporal dynamics. Our results indicate a rapid increase in humpback whale abundance in the Bransfield and Gerlache Straits through December, reaching a stable abundance by mid-January. The distribution of humpback whales appeared to change from a patchier distribution in the northern Gerlache Strait to a significantly concentrated presence in the central Gerlache and southern Bransfield Straits, followed by a subsequent dispersion throughout the area. Abundance estimates agreed well with previous literature, increasing from approximately 7000 individuals in 2000 to a peak of 19,107 in 2020. Based on these estimates, we project a total krill consumption of between 1.4 and 3.7 million tons based on traditional and contemporary literature on per capita krill consumption of whales, respectively. When taken in the context of krill fishery catch data in the study area, we conclude that there is minimal spatiotemporal overlap between humpback whales and fishery activity during our study period of November–January. However, there is potential for significant interaction between the two later in the feeding season, but cetacean survey efforts need to be extended into late season in order to fully characterize this potential overlap.

Published in

Ecology and Evolution

2022

Authors

John Elling Deehr Johannessen, Martin Biuw, Ulf Lindstrøm, Victoria Marja Sofia Ollus, Lucía Martina Martín López, Kalliopi C. Gkikopoulou, Wessel Chris Oosthuizen, Andrew Lowther

Institutions

Department of Arctic Biology, The Arctic University of TromsøNorwegian Polar InstituteInstitute of Marine ResearchSchool of Environmental SciencesSea Mammal Research UnitUniversity of Cape Town

Methods

Biological sampling DataField

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