Patterns in the Acoustic Presence and Vocal Behaviour of Bowhead Whales Balaena mysticetus in Eastern Fram Strait

• Main Authors: Katharina, Hiemer, Karolin, Thomisch
• Format: Thesis
• Language: unknown
• Published: 2019
• Subjects: Arctic; Greenland; Svalbard; Balaena mysticetus; bowhead whale; Fram Strait; Sea ice; Spitsbergen
• Online Access: https://epic.awi.de/id/eprint/50961/; https://epic.awi.de/id/eprint/50961/1/20190930_Hiemer_MSc.pdf; https://hdl.handle.net/10013/epic.e9a0778d-1feb-45b4-b383-b0a3a60c3beb; https://hdl.handle.net/

Fram Strait, located between Greenland and Svalbard, provides a critical habitat to seasonally migrant and endemic cetaceans, including bowhead whales Balaena mysticetus of the Spitsbergen population. This population has been depleted close to the point of extinction by commercial whaling and still is considered as endangered. Due to its low abundance and the remoteness of its habitat, baseline knowledge on spatio-temporal distribution patterns and behavioural aspects are scarce, yet crucial for the conservation of this population. Long-term passive acoustic recordings were collected at different locations in eastern Fram Strait (78-79°N, 0-7°E), contributing to the Ocean Observing System FRAM (Frontiers in Arctic Marine Monitoring). Data recorded during two sampling periods between 2012 and 2017 were analysed for the occurrence of bowhead whales using the Low-Frequency Detection and Classification System (LFDCS). Seasonal changes in their acoustic repertoire were investigated using recordings from a single year and location. Bowhead whales were acoustically present from autumn throughout winter (October/November-February) and occasionally in spring (March-June), suggesting that Fram Strait is used as an overwintering area. Given that peak levels of acoustic presence coincided with the presumed mating period of bowhead whales, Fram Strait may also serve as a mating area. No bowhead whales were recorded in summer (July-September), indicating that they either were vocally inactive or had migrated to summering areas. Eight distinct song types of bowhead whales were identified comprising simple songs and call sequences. Even though more than one song type was recorded at a given time, there was an overall trend that songs occurred in temporal succession. It remains speculative why songs appeared and subsequently disappeared with the progressing season, but the temporal succession possibly is related to the song types being used in different behavioural contexts. One song type formed an exception as it was recorded throughout almost the entire season and may hence serve a communicative function common to all individuals, or at a least a large part of the population. In contrast to previous studies on bowhead whales in western Fram Strait, the recorded bowhead whale detections were less frequent and, in addition, less complex. Bowhead whales appear to preferentially occupy the western part of Fram Strait where sea ice concentrations are generally higher. Due to the observed regional differences in the acoustic behaviour between eastern and western Fram Strait, eastern Fram Strait may represent the easterly distribution range boundary of the bowhead whale overwintering area. The findings of this study further highlight the importance of Fram Strait as a habitat for the endangered Spitsbergen bowhead whale population. In the light of rapid changes in the Arctic region, an improved understanding of distribution patterns and the acoustic behaviour is of particular relevance for developing effective conservation and management strategies, but also for assessing potential effects on the bowhead whale population resulting from climate-induced environmental changes.