Fluke chances: abundance estimates for humpback whales in Bermudian waters

• Main Authors: Tom Grove, Andrew Stevenson
• Format: Lecture
• Language: unknown
• Published: Zenodo 2021
• Subjects: North Atlantic
• Online Access: https://doi.org/10.5281/zenodo.5575269

Bermuda is a key stopover for migrating North Atlantic humpback whales, with connections to all major feeding and breeding grounds in the population. Despite these connections, and the designation of Bermuda’s exclusive economic zone as a Marine Mammal Sanctuary, the importance of these waters as a stopover had not been confirmed through abundance estimates. Here, we present our collaborative efforts to reconstruct annual abundance across the decade 2011-2020. Photo-identification data were collected annually by Whales Bermuda, using a small research vessel in coastal and offshore waters around the island. To-date, 1750 whales have been recorded. From this data set, the University of Edinburgh reconstructed abundance using a capture-recapture framework (the Cormack-Jolly-Seber model). From a set of models, a candidate which accounted for variation in survey effort and transience (animals only visiting Bermuda once) was selected. Abundance varied from 690 (CI 538-911) in 2016 to 1505 (CI 1182-2045) in 2018, confirming Bermuda’s stopover importance, with large inter-annual fluctuations. This confirmation may support underpin area-based management tools to mitigate risks from increasing human activities such as marine wildlife tourism, shipping and commercial fishing, in the waters around Bermuda. Furthermore, due to Bermuda’s migratory connections throughout the North Atlantic, this time series may be used to monitor species response to ecosystem change across an entire ocean basin.