Diverse foraging strategies by a marine top predator: Sperm whales exploit pelagic and demersal habitats in the Kaikōura submarine canyon

Abstract

The submarine canyon off Kaikōura (New Zealand) is an extremely productive deep-sea habitat, and an important foraging ground for male sperm whales (Physeter macrocephalus). We used highresolution archival tags to study the diving behaviour of sperm whales, and used the echoes from their echolocation sounds to estimate their distance from the seafloor. Diving depths and distance above the seafloor were obtained for 28 dives from six individuals. Whales foraged at depths between 284 and 1433 m, targeting mesopelagic and demersal prey layers. The majority of foraging buzzes occurred within one of three vertical strata: within 50 m of the seafloor, mid-water at depths of 700-900 m, and mid-water at depths of 400-600 m. Sperm whales sampled during this study performed more demersal foraging than that reported in any previous studies -including at Kaikōura in further inshore waters. This suggests that the extreme benthic productivity of the Kaikōura Canyon is reflected in the trophic preferences of these massive top predators. We found some evidence for circadian patterns in the foraging behaviour of sperm whales, which might be related to vertical movements of their prey following the deep scattering layer. We explored the ecological implications of the whales' foraging preferences on their habitat use, highlighting the need for further research on how submarine canyons facilitate top predator hotspots.

Modelling the spatial distribution of cetaceans in New Zealand waters

“…Offshore species and migratory species, e.g., minke, sei, sperm, killer, humpback and pilot whales, were more generalist and tended to show preference for depth related environmental variables over temperature related variables. Sperm and pilot whale preferences for deeper offshore waters around New Zealand are indicative of the location of their preferred prey, deep‐water squids and mesopelagic fishes often associated with canyons and trenches (Beatson, O'Shea, & Ogle, ; Gaskin & Cawthorn, ; Giorli & Goetz, ; Guerra et al, ). Minke and sei whales' habitat use patterns are poorly known in New Zealand (Baker et al, ), but it is likely they are migrating through New Zealand waters between southern feeding grounds and warmer water breeding grounds.…”

Movement and Biosonar Behavior During Prey Encounters Indicate That Male Sperm Whales Switch Foraging Strategy With Depth

“…Sperm whales could also take advantage of aggregations of terminally spawning cephalopods, and prefer slower, more gelatinous, neutrally buoyant cephalopod species that are easier to capture, despite lower caloric value (Clarke et al, 1993;Clarke, 1996). Interestingly, for sperm whales tagged in a highly productive submarine canyon in New Zealand, the opposite might be the case: benthic buzzes were on average longer (10-30 s) and produced at longer inter-buzz intervals compared to pelagic buzzes, suggesting availability of more calorific and/or agile prey at greater depths (900-1,200 m) (Guerra et al, 2017).…”

“…Sperm whales target mesopelagic and bathypelagic prey and can spend >70% of their time foraging (Watwood et al, 2006;Guerra et al, 2017). While cephalopods form the main component of the sperm whale diet, fish can be important regionally, such as in the high-latitude foraging grounds in in New Zealand (Gaskin and Cawthorn, 1967) and North Atlantic (Martin and Clarke, 1986).…”

Depression chains in seafloor of contrasting morphology, Atacama Trench margin: a comment on Marshet al.(2018)

“…The maximum dive depth recorded in cetaceans thus far has been 2992 m by a Cuvier's beaked whale [11]. These whales are probably physiologically capable of diving much deeper, as deep as 5000 m [12,13], and certainly spend extended periods close to the seafloor during foraging dives [14,15].…”