While most pinnipeds haul out on land to rest, give birth, and care for their young, Arctic dwelling seals rely instead on floating sea ice. Residing in harsh and remote territories, these seals have proven difficult to study in the wild, leaving many aspects of their behavior, physiology, and population status unknown. As the ice they depend on disappears at accelerating rates, a new urgency has fallen upon researchers to study these seals before their habitats and lifestyles are fundamentally altered. The PHOCAS program (Physiology and Health of Cooperating Arctic Seals) – a research partnership between the Alaska SeaLife Center (ASLC) and the University of California Santa Cruz – has spent the better part of the last decade in pursuit of this goal. With a special collection of ice-dependent seals under their care (most rescued from the wild following injury, stranding or abandonment), the team conducts research not otherwise feasible in the wild. Through their continued efforts, the PHOCAS team hopes to utilize their findings to understand how changes in the coming century might influence sub-Arctic and Arctic seals, and how we might be able to mitigate the negative impacts.
The team’s most recent publication summarizes a decade-long effort to record and document spotted seal vocal behavior. Like most marine mammals, spotted seals communicate using a series of vocalizations which travel efficiently under water. Using sensitive acoustic instruments, scientists can collect vocalizations and other sounds from marine habitats and compare them against existing databases, revealing the presence of species without need for direct visual observation. This has made acoustic recording an efficient tool for modern marine mammal research. Unfortunately, insufficient data on spotted seal vocalizations has necessitated their exclusion from acoustic monitoring studies in the past – a major barrier to studying these species in the wild, and a barrier that the PHOCAS team had set out to remove.
Opportunity arrived in 2010 when two male spotted seal rescue patients – later named Amak and Tunu – came to the SeaLife Center as newborn pups. After a rehabilitation period of several months, the young seals were determined to be non-releasable and transferred to Long Marine Laboratory at the University of California Santa Cruz for participation in cooperative behavioral research. As the seals progressed from young pups through adulthood, their sound production was studied by the PHOCAS team. Several patterns in their vocalizations were noted. Above-water calls, though present from the beginning, tended to increase as the seals matured. More notably, underwater calls were largely absent until around four years of age—their emergence coinciding with the onset of sexual maturity. Vocal behavior also followed a clear seasonal pattern, peaking in April (during the reported breeding season in wild spotted seals) and declining dramatically in the following month (coinciding with the end of the breeding season and the onset of the annual molt). Taken together, these patterns suggested an important role for underwater vocalizations in spotted seal breeding behaviors.
At five years old, Amak and Tunu returned to the ASLC as young adults for the study’s second chapter. While the PHOCAS team continued to monitor overall patterns in vocal behavior, recording equipment was also set up in the large seal exhibit at ASLC to allow for year-round audio monitoring. Using acoustic software to sort through and separate the recordings into distinct call types, eight different calls were identified – four of which had not been documented in any previous study. Each call was given a name corresponding to its sound: growl, knock, burp, pulse, grunt, rumble, drums, and moan.
As observed when the seals were younger, Amak and Tunu’s underwater vocalizations continued to peak in April and drop off in mid-May – appearing to sync up with breeding patterns observed in free-ranging spotted seals. To investigate this relationship further, the ASLC team tracked the seals’ reproductive states. They opportunistically collected urine samples and, in some cases, found sperm on slides viewed by microscope. The presence of sperm in their urine verified the seals’ heightened reproductive status in springtime, with additional indicators (urogenital swelling, aggressive behavior, and a strong musky odor) all showing a similar seasonal rise and fall.
Upon the study’s conclusion, the PHOCAS team had successfully documented a predictable repertoire of call types, the emergence of vocal behavior during maturation, and consistent patterns in the production of underwater calls by male spotted seals. These valuable data will improve acoustic tracking of spotted seals in the wild, and allow for more targeted data collection to maximize the chance of capturing vocalizations in the wild. Though there is much still to be learned, these findings are an important step towards a more nuanced understanding of Alaskan ice seals, offering tools for future research and bringing scientists closer to effective conservation strategies. In the face of ongoing climate trends and inevitable changes to ice seal habitats, these strategies are only set to grow in importance.
Want to learn more about this study? Check out the full publication here
Written by: Peter Sculli