Signals from the south; humpback whales carry messages of Antarctic sea‐ice ecosystem variability

• Published in: Global change biology 2018-04, Vol.24 (4), p.1500-1510
• Main Authors: Bengtson Nash, Susan M., Castrillon, Juliana, Eisenmann, Pascale, Fry, Brian, Shuker, Jon D., Cropp, Roger A., Dawson, Amanda, Bignert, Anders, Bohlin‐Nizzetto, Pernilla, Waugh, Courtney A., Polkinghorne, Bradley J., Dalle Luche, Greta, McLagan, David
• Format: Article
• Language: English
• Subjects: Adipose tissue; adiposity; Animal migration; Antarctic sea‐ice ecosystem; Aquatic mammals; Biochemical markers; biomonitoring; Climate; Climate change; Diet; Ecosystems; Environmental changes; humpback whales; Ice; Ice environments; Krill; Marine crustaceans; Marine environment; Marine mammals; Markers; Megaptera; persistent organic pollutants; Polar environments; Prey; sentinel; Southern Hemisphere; Southern Ocean; Stable isotopes; Trophic levels; Variation; Whales; Whales & whaling
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.14035

Southern hemisphere humpback whales (Megaptera novaeangliae) rely on summer prey abundance of Antarctic krill (Euphausia superba) to fuel one of the longest‐known mammalian migrations on the planet. It is hypothesized that this species, already adapted to endure metabolic extremes, will be one of the first Antarctic consumers to show measurable physiological change in response to fluctuating prey availability in a changing climate; and as such, a powerful sentinel candidate for the Antarctic sea‐ice ecosystem. Here, we targeted the sentinel parameters of humpback whale adiposity and diet, using novel, as well as established, chemical and biochemical markers, and assembled a time trend spanning 8 years. We show the synchronous, inter‐annual oscillation of two measures of humpback whale adiposity with Southern Ocean environmental variables and climate indices. Furthermore, bulk stable isotope signatures provide clear indication of dietary compensation strategies, or a lower trophic level isotopic change, following years indicated as leaner years for the whales. The observed synchronicity of humpback whale adiposity and dietary markers, with climate patterns in the Southern Ocean, lends strength to the role of humpback whales as powerful Antarctic sea‐ice ecosystem sentinels. The work carries significant potential to reform current ecosystem surveillance in the Antarctic region. Novel, non‐lethal, chemical and biochemical markers were developed and implemented for long‐term sentinel monitoring of southern hemisphere humpback whales. The “sentinel parameters” of adiposity and diet oscillated closely with climatic conditions in the populations’ corresponding Antarctic feeding ground over the 8‐year monitoring period. On the basis of these findings, implementation of southern hemisphere humpback whales for long‐term, circum‐Antarctic sea‐ice ecosystem surveillance is advocated.