Isotopic Evidence of a Wide Spectrum of Feeding Strategies in Southern Hemisphere Humpback Whale Baleen Records

Abstract

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 inter-annual 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.

Radiocarbon as a Novel Tracer of Extra-Antarctic Feeding in Southern Hemisphere Humpback Whales

“…2). This confirms the previous classification of these whales as Classical Feeders 31 .

Figure 2Bivariate representation of baleen Δ 14 C and δ 13 C in classical feeders. Coloured zones represent isotopic values for the Antarctic feeding grounds (gold, dashed line), and Australian feeding grounds (green, dotted line).

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“…While several plausible causation factors remained following traditional SI analysis 31 , complementary Δ 14 C analysis definitively showed the high δ 13 C values previously measured in some SHHWs baleen plates were indicative of feeding in two different regions.…”

Linking pollutant exposure of humpback whales breeding in the Indian Ocean to their feeding habits and feeding areas off Antarctica

“…(Eisenmann et al, 2016). Evidence of feeding in temperate waters and during partial migration was suggested in some individual whales from East Australian breeding population, pointing to some plasticity in prey selection (Eisenmann et al, 2016 (Zhao et al, 2004), the Weddell seal Leptonychotes weddellii (Burns et al, 1998;Zhao et al, 2004), Type C killer whale Orcinus orca (Krahn et al, 2008), and the leopard seal Hydrurga leptonyx (HallAspland et al, 2005;Zhao et al, 2004) (Fig. 5).…”

Mercury and stable isotope cycles in baleen plates are consistent with year-round feeding in two bowhead whale (Balaena mysticetus) populations

“…Previous studies have shown that stable isotope ratios along baleen plates provide insight into seasonal movements between feeding grounds (Schell et al 1989a, b;Hobson and Schell 1998;Caraveo-Patiño et al 2007;Bentaleb et al 2011;Ryan et al 2013;Eisenmann et al 2016). For instance, the seasonal shift in stable isotope values evident in Southern right whale (Eubalaena australis) baleen indicates an annual migration over the south Atlantic convergence (Best and Schell 1996).…”