Isotopic Evidence of a Wide Spectrum of Feeding Strategies in Southern Hemisphere Humpback Whale Baleen Records
May
Isotopic Evidence of a Wide Spectrum of Feeding Strategies in Southern Hemisphere Humpback Whale Baleen Records
Pascale Eisenmann 0 1
Brian Fry 1
Carly Holyoake 1
Douglas Coughran 1
Steve Nicol 1
Susan Bengtson Nash 0 1
0 Environmental Futures Research Institute, Griffith University , Brisbane QLD 4111 , Australia , 2 Australian Rivers Institute, Griffith University , Brisbane QLD 4111 , Australia , 3 Murdoch University , Perth WA 6150 , Australia , 4 Department of Parks and Wildlife , Kensington WA 6151 , Australia , 5 Institute for Marine and Antarctic Studies, University of Tasmania , Hobart TAS 7000 , Australia
1 Editor: Elliott Lee Hazen, UC Santa Cruz Department of Ecology and Evolutionary Biology , UNITED STATES
Our current understanding of Southern hemisphere humpback whale (Megaptera novaeangliae) ecology assumes high-fidelity feeding on Antarctic krill in Antarctic waters during summer, followed by fasting during their annual migration to and from equatorial breeding grounds. An increase in the number of reported departures from this feeding/fasting model suggests that the current model may be oversimplified or, alternatively, undergoing contemporary change. Information about the feeding and fasting cycles of the two Australian breeding populations of humpback whales were obtained through stable isotope analysis of baleen plates from stranded adult individuals. Comparison of isotope profiles showed that individuals from the West Australian breeding population strongly adhered to the classical feeding model. By contrast, East Australian population individuals demonstrated greater heterogeneity in their feeding. On a spectrum from exclusive Antarctic feeding to exclusive feeding in temperate waters, three different strategies were assigned and discussed: classical feeders, supplemental feeders, and temperate zone feeders. Diversity in the interannual feeding strategies of humpback whales demonstrates the feeding plasticity of the species, but could also be indicative of changing dynamics within the Antarctic sea-ice ecosystem. This study presents the first investigation of trophodynamics in Southern hemisphere humpback whales derived from baleen plates, and further provides the first estimates of baleen plate elongation rates in the species.
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Data Availability Statement: All relevant data are
within the paper and its Supporting Information files.
Funding: This work was funded by a Pacific Life
Ocean Foundation Grant (https://www.oceanfdn.org/
partnerships/foundation/pacific-life-foundation)
awarded to SBN and Pascale Eisenmann
acknowledges two Griffith University (https://www.
griffith.edu.au) post-graduate (GUPRS) and
international (GUIPRS) scholarships. The funders
had no role in study design, data collection and
Introduction
Southern hemisphere humpback whales (SHHW) exhibit one of the longest mammalian
migration on Earth, travelling close to 10 000 kilometres between their equatorial breeding
grounds and Antarctic feeding grounds [
1–3
]. The classical feeding ecology model for these
analysis, decision to publish, or preparation of the
manuscript.
populations assumes high-fidelity summer feeding on Antarctic krill (Euphausia superba)
followed by fasting throughout the entire migration, with feeding only resumed in Antarctic
waters the following summer [
4–7
]. Because they are capital breeders, the humpback whales
breed, calve and nurse during the migratory fast. As such, the SHHWs rely on the presence of
high krill biomass to feed, and to replenish their blubber stores for a successful migration and
reproduction.
There are 7 distinct breeding stocks (A-G) of SHHW recognised by the International
Whaling Commission (IWC) [
8
]. The populations migrating along the western and eastern
Australian coasts are classified as the D and E1 breeding stocks, respectively (Fig 1) [
8
]. While
uncertainty still surrounds the extent and inter-annual consistency of the Antarctic feeding
grounds associated with both of these populations, mark-recapture data evidence led the IWC
to allocate feeding areas IV and V (Fig 1) to the D and E1 breeding stocks respectively. Tagging
evidence corroborates the significance of area V, which include the Balleny Islands, as a
summer feeding ground for the E1 population [
9, 10
].
The narrow feeding niche of SHHWs places them at an elevated risk of exposure to the
detrimental effects of climate-induced environmental change. In a warming climate, the Antarctic
cryosphere is expected to undergo dramatic change [
11, 12
]. Sea-ice represents a critical
nursing ground for Antarctic krill larvae, hence a decline in sea-ice cover and duration has been
predicted to have a devastating impact on Antarctic krill biomass [
13–15
]. One study has
predicted that unmitigated CO2 emissions will result in a complete collapse of Antarctic krill
stocks by the year 2300 [16]. Negative impacts to this keystone species carry repercussions for
Fig 1. Migration, feeding gro (...truncated)