Vocalizations in Pinnipeds

The pinniped family are social animals and display a wide range of vocalizations in social situations both underwater and above. In their natural habitat, they will use vocalizations for territory protection, mating, aggression, colony coordination, and pup identification. This group has proven their intelligence by being the only nonhuman primate to master vocal learning in captivity. Sounds of the vocalizations vary between each species and age.

Pinniped species will​ ​perform a variety of vocalization sounds including​ ​short barks, growls, grunts, roars, honks, moans, and pup ​contact calls​. These sounds make up individualized contact calls which are important for mating, pup recognition, group cohesion and movement coordination (Discovery of., 2018).​ The most evident and well-researched evidence of recognition in the pinnipeds is between a dependent pup and mother.​ ​Females will leave their pups ashore while they go on foraging trips. In order for a mother to relocate her own pup after completing a foraging trip, identifiable vocalizations are made in order to reunite the pair (Aubin, 2015). Different sensorial techniques are used in identifying an individual however, acoustic is the most efficient amongst a colony and over long distances ​(Discovery of., 2018).

The development of vocalizations can occur through two processes. First, learning through auditory experiences, such as imitating older pinnipeds. Secondly, development of vocalizations occurs in pinniped structural phenotype or body size. Age can factor into vocalization behaviors. As pinnipeds age, they tend to show more frequent and effective vocalizations as observed in captive settings (Galimberti et. al, 2008, p. 137-138). A recent study examined the development of vocalization in harbor seal pups (​Phoca vitulina richardii​). In the study, vocalization frequencies of 15 captive harbor seal pups were recorded using a spectrogram at The Marine Mammal Center in Sausalito, California. The pups were brought in from the wild for rehabilitation at the age of 1 – 7 days. In captive care, they were in vocal and physical contact with other harbor seal pups. Results showed that each vocalization is unique and individualized for each pup which helps a mother find her pup in a natural environment. Pups produced calls starting as early as 2 days postpartum. Significant differences between male and female pup calls were found. Male pup calls had a higher frequency than calls of female pups. Both sexes while young had similar frequency values, but as they matured, female calls became higher in frequency while male calls became lower. Sex vocalization differences have also been found in harp seal pups (​Phoca groenlandica). ​Aggressive calls made by both sexes had a higher frequency than mother attraction calls. The youngest pup age heard to make aggressive vocalizations was 16 days postpartum. Further research is needed to observe how aggressive vocalizations develop in harbor pups (Khan et. al, 2006, p. 1685).

Underwater behaviors and vocalizations of pinnipeds in the wild are hard to observe and capture, however captivity gives us a unique opportunity to observe these behaviors and vocalizations. A recent study observed underwater social behavior of harbor seals in California (n=388). Three types of underwater social behavior were observed: visual and acoustic, playful, and signal gestures. Visual and acoustic behaviors included vocalization, splashing, and blowing bubbles. Playful behavior was seen as rolling, mounting, and biting. Observed as signal gestures were head-thrusting, flipper scratching and growling​ ​(Nicholson, 2000, p. 2​). ​Many species within the pinniped family share these underwater behaviors as they socialize with each other and communicate.

Specific species in the pinniped family produce louder vocalizations during breeding season. According to (Schusterman et. al, 2001, p. 1-2), captive male California sea lions, male harbor seals, and female elephant seals are highly vocal during the breeding season and quieter during other times of the year. However, the production of these sounds using vocal and gestural cues have been able to be controlled by a trainer. In the wild, studies have recorded underwater breeding vocalization frequencies in several pinniped species. One study by (Asselin et. al, 2015), on grey seals (​Halichoerus grypus) s​howed that call types had seasonal variation and rate of vocalization increased during breeding season. In another study on ringed seals ​(Pusa hispida), ​all types of vocalizations increased during breeding season as well. Different sounds were made by different sexes. For example, long snorts were only produced by adult males directed towards adult females. Yelps, barks, and knock sounds were performed as submissive signals. These specific vocalizations continued through the breeding season but were not as frequent during the non-breeding period (Schusterman et. al, 1970, p. 303-305).

It has been observed that the main purpose of pinniped vocalization is to receive attention and dictate the behavior of other pinnipeds ​(Schusterman, 2001, p. 1-2). Pinnipeds use vocalization to communicate with their pup, for breeding, aggression, and to relay other messages. Future research is needed to gain more knowledge on pinniped vocalization in the wild, but captivity has helped researchers brush the surface on understanding their complex communication system.

References
Asselin, S., Hammill, M. O., & Barrette, C. (1993). Underwater vocalizations of ice

breeding grey seals. ​Canadian Journal of Zoology,​ ​71​(11), 2211-2219.

Aubin, T., Jouventin, P., & Charrier, I. (2015). Mother vocal recognition in Antarctic fur seal Arctocephalus gazella pups: a two-step process. ​PloS one​, ​10​(9), e0134513.

Galimberti, F., Sanvito, S., & Miller, E. (2008). Development of aggressive vocalizations in male southern elephant seals (Mirounga leonina): maturation or learning?. ​Behaviour,​ ​145(​ 2), 137-170.

Khan, C. B., Markowitz, H., & McCowan, B. (2006). Vocal development in captive harbor seal pups, Phoca vitulina richardii: Age, sex, and individual differences. The Journal of the Acoustical Society of America​, ​120(​ 3), 1684-1694.

Nicholson, T. E. (2000). ​Social structure and underwater behavior of harbor seals in southern Monterey Bay, California​ (Doctoral dissertation, San Francisco State University).

Schusterman, R. J., Balliet, R. F., & John, S. S. (1970). Vocal displays under water by the gray seal, the harbor seal,. and the stellar sea lion. ​Psychonomic Science​, 18​(5), 303-305.

Schusterman, R. J., Southall, B. L., Kastak, D., & Reichmuth Kastak, C. (2001). Pinniped vocal communication: form and function. In ​Proceedings of the 17th International Congress on Acoustics, Rome, Italy​ (pp. 1-2).

The University of Rhode Island. (2018). Harbor Seal. ​Discovery of Sound in the Sea​/. Retrieved from https://dosits.org/galleries/audio-gallery/marine-mammals/pinnipeds/harbor-s eal/

Research review paper by summer intern Catherine Y. Catherine is a student at Texas A&M University studying Marine Biology.