Critical threshold identified in the functional relationship between beaked whales and their prey

Abstract

Anthropogenic noise is increasingly recognized as a potentially significant stressor for marine animals. Beaked whales, deep-diving cephalopod predators, have been disproportionally present in atypical mass stranding events coincident with military sonar exercises, while frequently disturbed populations that do not strand may have reductions in fitness. We present in situ measures of prey availability, a key factor affecting fitness, for 2 distinct populations of Mesoplodon densirostris: one on a US Navy range in The Bahamas and one nearby in an area less exposed to sonar. The variables most strongly correlated with beaked whale habitat use were related to the distribution of deep-sea squid (mode spacing, peak depth, and 100 m scale variability). All squid metrics were more favorable for beaked whales at the less exposed site than those on the range. To develop a generalized functional relationship between prey resources and beaked whale habitat use, data from The Bahamas were combined with comparable data from another Navy range and the larger beaked whale, Ziphius cavirostris. A power-law relationship was observed between a normalized metric of prey quality and whale habitat use. A critical threshold in prey characteristics, below which beaked whales appear unlikely to be successful, but above which small changes in resource availability enable large gains for predators, was observed. This implies that modest changes in the behavior of individual whales associated with disturbance can have consequential population effects. Our results elucidate the ecological realities of these elusive and sensitive beaked whales, and the importance of environmental context in effective spatial planning for the deep sea.

Echolocation click parameters and biosonar behaviour of the dwarf sperm whale (Kogia sima)

“…Here, intense surface and diffuse deep scattering layers were identified at depths of ∼120 and ∼540 m, respectively, during the daytime, becoming more intense and migrating shallower at night (Sato and Benoit-Bird, 2017). Our sampling location has been identified as a high-quality foraging habitat for odontocetes, with high density in mesopelagic scattering layers at ∼150 and ∼700-800 m (Benoit-Bird et al, 2020). Thus, the depths of both our array and the majority of our Kogia localizations (Table 1) overlap with scattering layers at this location, supporting our hypothesis that they are foraging in acoustically cluttered prey layers.…”

Deep-sea predator niche segregation revealed by combined cetacean biologging and eDNA analysis of cephalopod prey

“…Combined data on deep-sea prey spectra available in cetacean target foraging zones also represent critical knowledge aiding in the understanding of marine top predator foraging performance and how this may change under disturbance settings. Absence of knowledge on prey communities has been identified as a limiting factor in the understanding of population-level effects of predator behavioral responses causing impeded foraging, particularly for beaked whales, which are highly sensitive to disturbance from anthropogenic noise ( 46 , 47 ).…”

An Acoustic Survey of Beaked Whales and Kogia spp. in the Mariana Archipelago Using Drifting Recorders

“…Abecassis et al (2015) found that a high density of midwater micronekton was an important covariate for Blainville's beaked whale distribution off the island of Hawai'i, likely because it represents the prey for beaked whale food sources. Benoit-Bird et al (2020) found that additional oceanographic features highly correlated with beaked whale habitat were associated to deep-sea squid habitat, highlighting the importance of these focused food sources. When Suntsov and Domokos (2013) sampled micronekton and macro zooplankton on three meridional transects between 10 • N and 17 • N in the Mariana Archipelago, they found relatively low concentrations within the oligotrophic NEC suggesting the prey availability for beaked whale and Kogia spp.…”