3 March Array Servicing Exped

Download the full report here: Expedition Report Array Servicing 2018

Executive Summary

The British Indian Ocean Territory (BIOT) is among the largest no-take contiguous  marine protected areas in the world. In recent years the marine ecosystems of BIOT have faced growing challenges posed by increasing water temperatures and more extreme climatic events threatening to disrupt the complex balance of life harboured by the remote atoll systems that comprise the Chagos Archipelago. As a component of the Bertarelli Program in Marine Science (BPMS), researchers from Stanford University, the University of Western Australia and the Zoological Society of London have established one of the key monitoring platforms for assessing how some of the largest predatory fish in BIOT are responding to their changing environment and threats posed by illegal fishing activity. Using acoustic and satellite tracking technologies the team can observe the movements, distribution, residency and connectivity of mobile marine predators both close to the reef and during excursions into deeper pelagic waters. A spatially extensive network of acoustic receivers has been monitoring tagged fish, sharks and manta rays for approximately six years providing invaluable long-term data for addressing changes in these marine megafauna communities. In addition, new genetic techniques (eDNA) are now being employed alongside our technology to explore community composition over broad spatial scales and monitor the physical and biogeochemical processes shaping the ecosystems of BIOT. In order to maintain the continuity of data gathered via our archival acoustic monitoring array our receivers require regular servicing to ensure continuous functioning of the array. In March 2018 we undertook a research expedition aboard the RV Tethys Supporter for X days.

Similar to previous years, the expedition objectives included servicing the entire receiver array and deploying a new cohort of long-term acoustic and shorter-term satellite tags. With the assistance of the crew aboard R/V Tethys and under somewhat challenging time and weather constraints, the team deployed tags on 71 sharks from four different reef associated species. In total, 81 individual tags were deployed, with 10 individuals double tagged with both pop-up satellite tags in addition to the acoustic tags. The team was able to recover, download and redeploy 43 VR2W receivers and 1 underwater modem unit, yielding over 370,000 new detections to contribute to the time-series. In addition, two VR4 Global units were serviced with new moorings, ensuring continued live feeds of acoustic data. Following the success of the previous deployments and retrieval of acoustic release receivers (VR2AR) deployed beyond diveable depths – for example on the submerged seamounts of Sandes’ and Swart’s four AR units were deployed near the original locations from 2016. The team collected water samples for eDNA from 20 separate receiver and tagging locations. The samples were filtered on site and frozen for next generation sequencing at Stanford. In addition the team took still images, video, 360° and drone-based footage to contribute to the BPMS media library and for all up and coming outreach events. The expedition was covered on several social media platforms with three blogs written from the field ensure that the work of the BPMS in BIOT reaches a broad audience. The data gathered from this recent expedition will contribute to many research projects and papers as the BPMS moves forward into its next phase. Importantly, these continued data, combined with environmental monitoring and enforcement data, enable us to assess the impact the MPA and the changing climate is having on our marine predator guilds and continue to make BIOT a benchmark for ocean monitoring in the Indian Ocean.