Acoustic crypsis in southern right whale mother–calf pairs: infrequent, low-output calls to avoid predation?

Abstract

ABSTRACT Southern right whales (Eubalaena australis) invest substantial amounts of energy in their calves, while facing the risk of having them predated upon by eavesdropping killer whales (Orcinus orca). We tested the hypothesis that southern right whale mother–calf pairs employ acoustic crypsis to reduce acoustic detectability by such predators. Specifically, we deployed multi-sensor DTAGs on nine lactating whales for a total of 62.9\u2005h in a Western Australian breeding ground, and used a SoundTrap to estimate the concomitant acoustic background noise. Vocalisations were recorded at low rates of <10\u2005calls\u2005h−1 (1 call per dive) and at low received levels between 123±8 and 134±10\u2005dB re. 1\u2005µPa RMS depending on call type. We conclude that such acoustic crypsis in southern right whales and other baleen whales decreases the risk of alerting potential predators and hence jeopardizing a substantial energetic investment by the mother. Highlighted Article: Low-output infrequent calls in baleen whale mother–calf pairs may mediate contact between mother and calf, while decreasing the risk of detection by potential predators.