Humpback whale feeding behavior and defecation observed on the Hawaiian breeding grounds Marine Mammal Science

The traditional paradigm of humpback whale (Megaptera novaeangliae) behavior involves migration annually between low latitude breeding grounds and high latitude feeding grounds, with limited or no feeding during migration (see Owen et al., 2017), and individuals fasting on the breeding grounds (e.g., Baker et al., 1986; Chittleborough, 1965; Clapham, 2000; Dawbin 1966; Katona & Beard, 1990; cf. Mikhalev, 1997). Humpback whales have been recognized as dietary generalists since the examination of stomach contents during commercial whaling operations (e.g., Clapham et al., 1997). While at high latitudes in the northern hemisphere, humpback whales, known commonly as lunge feeders, typically consume krill (Euphausia sp.) and small schooling fish such as capelin (Mallotus villosus), herring (Clupea sp.), sand-lance (Ammodytes sp.), and juvenile salmon (Oncorhynchus sp.) (Straley et al., 2018; Szabo, 2015; Witteveen et al., 2008, 2011; Reidy et al., 2022). In the southern hemisphere, researchers have historically maintained that humpback whales rely largely on Antarctic krill (Euphausia superba; Groß et al., 2020). However, recent data employing stable isotope techniques have revealed that like the northern hemisphere humpbacks, they too are generalists (Bury et al., 2024), exploiting small schooling fish such as jack mackerel (Trachurus declivis), pilchards (Sardinops neopilchardus), and redbait (Emmelichthy nitidus) along their migration route (Owen et al., 2017). Shifts in the dominant prey source in response to location, variations in ocean temperatures and ecosystem conditions reinforces this dietary flexibility (Fleming et al., 2016). Humpback whales and other baleen whales are considered capital breeders, and during migration and breeding, their metabolic needs are thought to be met by breakdown of adipose tissue, resulting in a loss of body mass while migrating thousands of kilometers and engaging in breeding behaviors (Christiansen et al., 2016).