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SC/69B/SH/04
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Resource ID
22147
Access
Open
Document Number
SC/69B/SH/04
Full Title
Most ?flight? baleen whale species are acoustically cryptic to killer whales, unlike ?fight? species
Author
Trevor A. Branch
Authors Summary
Baleen whales can be divided into ?fight? and ?flight? species based on their reactions to killer whale attacks. Fight species generally aggregate coastally in winter to breed, while flight species disperse offshore. Since fight species return reliably to the same areas to calve and mate, their male singing is likely geared to compete with other males; while flight species need to attract distant females. Evidence is presented that fight species typically sing at higher frequencies and loudly enough to be heard by distant killer whales, while most flight species sing at low frequencies or quietly, and cannot be easily heard by distant killer whales.
Publisher
IWC
Publication Year
2024
Abstract
Baleen whales can be divided into ?fight? and ?flight? species based on their reactions to killer whale attacks. Flight species are slow-moving, maneuverable, displaying group or single defense against attacks on their calves, and migrating and breeding in denser aggregations in shallow coastal waters. Flight species are sleek, fast-swimming, flee on contact with killer whales, and migrate and breed while dispersed in pelagic waters. One corollary to this hypothesis is that male singing in fight species should involve competition among groups with more colorful and interesting singing, while in flight species, males should sing loudly and more monotonously to attract distant mates. Since fight species rely somewhat on group defense and return reliably to the same areas to calve and mate, they do not need to hide acoustically from killer whales; but loud-singing flight species would be more susceptible to being located by killer whales. This suggests a possible role for acoustic crypsis, which has been reported for some species of toothed whales that only call at frequencies that are too high for killer whales to hear. Here I examine whether the calls of baleen whale flight species (unlike fight species) call at low frequencies that are difficult (<1500 Hz) or impossible (<100 Hz) for killer whales to hear. A review shows that five out of six fight species call at higher frequencies ( 4000 Hz) and with high source levels (>175 dB re 1 ?Pa at 1 m) and can be heard by killer whales from at least 100 km away, while sixth fight species (gray whales), frequently attacked by killer whales on migration, call at quieter source levels (157 dB) and can be heard only within 15 km. For flight species, the opposite pattern is clear: six out of eight flight (or likely flight) species call with some combination of low frequencies (<1000 Hz) or low source levels ( 175 dB), such that they are either acoustically invisible to killer whales or can only be heard by nearby (<10 km) killer whales.