Marine mammal research in the Dutch Caribbean, 2010-2024

In the last decades the importance of the Caribbean for marine mammals has been increasingly recognised leading to a range of international conservation efforts. The Netherlands has been a partner in international projects to improve our understanding of marine mammals, primarily cetaceans, in the Dutch Caribbean waters and beyond. In 2015 the Netherlands established the Yarari Shark and Marine Mammal Sanctuary, comprising waters of Bonaire and the Leeward islands Saba and Sint Eustatius (since 2018). The aim of this Marine Protected Area (MPA) is to: “ensure the protection of marine mammals and sharks and their habitats from negative impacts of human activities, whether direct or indirect, actual or potential"'. Effective conservation and management depend on reliable baseline data on cetacean occurrence as well as the risks they face. Unfortunately, as wide-ranging species that spend a considerable time of their lives under water, cetaceans can be challenging to study. We summarize different methodological approaches that have been used in Dutch Caribbean waters, such as photo identification, designated surveys and the collection of opportunistic sightings and stranding data. We also present the most recent results from the Passive Acoustic Monitoring (PAM) that is conducted within the current management framework. PAM was deployed consistently from 2016 to 2024, yielding a large wealth of data. This method has been shown to allow long-term monitoring of the occurrence of cetaceans (and other taxa). This report provides a summary and update of the data collected on the Saba Bank, in the northern branch of the Yarari Sanctuary, as well as of the development and testing of new analytical approaches. The PAM results showed amongst others that humpback whales are consistently present in the Saba Bank area from January to May. Humpback whale vocalizations were recorded during the reproduction period, which is a sensitive time in the species' life cycle. Management of the Yarari Sanctuary should take this into account. Considering the available resources regarding both funding and logistics, we propose to continue to prioritize the PAM research efforts in the Dutch Caribbean. Focussing on this method allows us to develop cost-effective automated data analyses, to extend the sampling stations and to continue to work together towards an international Caribbean acoustic database.