In-air acoustic repertoire and associated behaviour of wild juvenile crabeater seals during rehabilitation

ABSTRACT

In-air sounds of pinnipeds are important for interactions with conspecifics and threat displays. However, little is known about the in-air acoustic repertoire and associated behaviour of crabeater seals Lobodon carcinophaga. We investigated the in-air acoustic repertoire and associated behaviour of two male and one female wild juvenile crabeater seals that beached separately, and were rehabilitated in Durban and Gqeberha, South Africa. In-air sounds were visually identified and categorised into five classes validated via random forest model classification: brief, intermediate, and long moan calls, croaks, and hisses. Hisses were common (n = 25,105 sounds from 136 hrs of acoustic recordings) and detected during heightened arousal states and interactions with animal care staff and a conspecific. Furthermore, hisses were also recorded in low arousal states during exhalation. Moan calls (n = 241) were only detected from two of the three seals. During rehabilitation, the female seal ceased producing moan calls and later produced a series of croaks (n = 204). Acoustic characteristics of in-air moan calls differed from published underwater moan calls according to duration, minimum, and maximum frequencies, and pulse repetition rate. Our study shows that the in-air acoustic repertoire and associated behaviour of these Antarctic seals are dynamic, vary inter-individually and are context dependent.

KEYWORDS:

• Acoustic behaviour
• Lobodon carcinophaga
• Antarctic pinnipeds
• acoustic repertoire
• in-air sounds
• South Africa

Acknowledgements

We acknowledge Werner Conradie for the use of the recorder and handheld microphone to collect acoustic data in Gqeberha. uShaka Sea World (a division of the South African Association for Marine Biological Research) and Bayworld are thanked for allowing the recording of acoustic data. We are grateful to animal care staff at Bayworld and uShaka Sea World for their expertise and hard work in rehabilitating the seals. Many thanks to Dr Dawit Yemane for his kind assistance with the statistical data analyses. Numerous citizen scientists are sincerely appreciated for volunteering their valuable time to assist with seal observations and sound recording under challenging weather conditions in Gqeberha. Final thanks go to the two anonymous reviewers for their constructive comments on earlier version of this manuscript.

Data availability

Most data are available in the main text, and provision of raw data will be considered on a reasonable request.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical statement

Ragnar was captured and rehabilitated under Permit No. S03156 issued to the South African Association for Marine Biological Research by the Department of Forestry, Fisheries and the Environment (DFFE) in terms of the National Environmental Management Biodiversity Act 2004 (Act 10 of 2004). Sebastian and Pearl were captured and housed under Permit No. S03169 in terms of the National Environmental Management Biodiversity Act 2004 (Act 10 of 2004) and Permit No. RES2021–29 issued to the Port Elizabeth Museum at Bayworld by the DFFE in terms of the Marine Living Resources Act 1998 (Act 18 of 1998). Both facilities are accredited members of Pan African Association of Zoos and Aquaria. All individuals observed in this study were captured, transported to the rehabilitation facilities, rehabilitated, and later released alive at sea, with due regard to animal welfare by experienced staff.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/09524622.2022.2108145.