Seasonal distribution of sperm whales in the High Arctic revealed by multi-year passive acoustic monitoring

Abstract

The sperm whale (Physeter macrocephalus) is a cosmopolitan species with a broad distribution that ranges from the tropics to the poles. Males are known to migrate between nutrient-rich high latitude waters and low latitude breeding grounds. In the North Atlantic, large males are found up to the southern limits of the ice edge. However, their seasonal distribution patterns remain poorly known in the High Arctic, where year-round monitoring is challenging. To investigate the presence of this highly vocal species in the High Arctic, this study used passive acoustic data collected from nine different locations around Svalbard Archipelago from 2012 to 2021. An automated sperm whale click detector was designed and implemented using PAMGuard and R to identify time periods containing sperm whale vocalizations. Automatic detection results were then manually confirmed; different click types were also scored, and the number of vocalizing individuals was estimated. The results show sperm whale presence at almost all recording sites and indicate sperm whale “hotspots” along the ice-free portion of eastern Fram Strait (along the shelf break) and close to the coast of western Spitsbergen from May to January, with some variation between years and moorings. Although the acoustic presence decreased further north, even the northern-most location (81°N) had sperm whales present from August to as late as January during no or low ice periods of the year. Sperm whale click detections were less frequent in fjord locations and off the east coast of Svalbard. This study is a first multi-year acoustic assessment of sperm whale distribution in the High Arctic. It provides valuable baseline information on the distribution of sperm whales, a migratory species that is frequently present in the High Arctic. Such knowledge is interesting in the context of understanding and predicting future patterns of cetacean distribution in the rapidly changing Arctic marine environment.

Popular Abstract

Eavesdropping on the secret life of sperm whales in the High Arctic

The sperm whale (Physeter macrocephalus) is a cosmopolitan species found in all oceans, from the tropics to the poles. Females and calves are known to inhabit warmer, low-latitude breeding grounds in distinct social groups, while mature male individuals undergo long migrations to the nutrient-rich high latitude waters. While sperm whales have been observed regularly in the High Arctic, around the Svalbard Archipelago, very little is known about the actual timing or geographic extent of their visits. Monitoring this species in the High Arctic waters is challenging not only because sperm whales inhabit deep offshore waters and perform long dives but also because of limited year-round access for data collection in the area due to sea ice and polar night.

Sperm whales are very vocal and use different click sounds for echolocation (navigation, foraging) and communication. This makes sperm whales an excellent candidate for acoustic monitoring: By listening and identifying sperm whale sounds in underwater acoustic recordings, we can assess their vocal presence (or absence) in the area. This study used data recorded with hydrophones attached to oceanographic data collection platforms anchored at eight locations around the Svalbard Archipelago, across a 10-year time span. The data were analyzed, to identify sperm whale sounds and, consequently, determine sperm whale presence. The High Arctic soundscape is not silent, but known to be complex, comprising a variety of biological, geophysical, and anthropogenic sound sources. To find sperm whale sounds in the recordings, an automated detector was used, and finally the automatic detections were confirmed manually. Additionally, presence of different click types and occurrence of simultaneous vocalizations from more than one individual was assessed.

The results showed sperm whale presence at most recording sites. Two “hotspots” were identified off western Svalbard, where sperm whales were present at deep, shelf-edge areas almost year-round. Even at the northern-most recording site (81N), sperm whales were present consistently during ice-free or low ice cover periods. Three different click types were heard at almost all sites with sperm whale presence: Usual clicks and buzz clicks, linked to navigation and foraging, were expected, as these animals are there to forage and feed. However, the consistent occurrence of “slow clicks”, a click type associated with socializing and communication, was rather surprising. This supports the idea of loose aggregations of males and potential socializing in the High Arctic rather than solitary behavior.

The High Arctic is one of the most rapidly changing environments, and extensive and increasing loss of sea ice cover has already been documented. The already reported northward shift in sperm whale distribution is likely to continue. The results of this study provide a baseline for future acoustic monitoring in the High Arctic, which will be crucial for predicting change and advising management authorities given the rapidly changing environment.

Master’s Degree Project in Biology, 60 credits
Department of Biology, Lund University
Supervisors: Heidi Ahonen, Kit Kovacs, Christian Lydersen (Norwegian Polar Institute)
Karolin Thomisch (Alfred Wegener Institute)

• author: Pöyhönen, Viivi
• supervisor: Heidi Ahonen; Kit Kovacs
• organization: Degree Projects in Biology
• course: BION03 20221
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9113480
• date added to LUP: 2023-04-14 13:44:37
• date last changed: 2023-04-14 13:44:37