The importance of the Chagos Archipelago for top predators in the Indian Ocean

Top predators are crucial as regulators of our oceans and indicators of healthy ecosystems. Yet, top predators such as tunas and sharks are under increasing pressure from fisheries, energy extraction and climate change. Moreover, we have a very limited understanding of their population ecology which in turn hinders our ability to manage them effectively.

 

Recently, MPAs have been increasing both in number and size but only a few empirical studies have investigated their effectiveness and use for protecting its mobile marine predators. To address this, we have been collaborating on a long-term interdisciplinary predator research programme around the Chagos Archipelago as part of the Bertarelli Foundation's Marine.Science programme since 2013. Through a combination of biologging, telemetry, chemical tracer analysis (stable isotopes and genomics), applied fisheries science, oceanography and environmental DNA surveys, we are assessing the effectiveness of the British Indian Ocean Territory’s (BIOT) Marine Protected Area (MPA) that surrounds the Chagos Archipelago in protecting it's top predators. To do so, we have had the following key research objectives:

 

1. Evaluate the health and status of local reef shark communities in the context of regional populations

2. Understand the drivers of predator behaviour and distributions around the Chagos Archipelago

3. Characterize predator-mediated ecosystem connectivity across the MPA through shark movements

4. Quantify the degree of connectivity between the archipelago's rich predator community and the wider Indian Ocean populations

5. Assess the impact of the MPA's establishment in 2010 on regional predator populations and surrounding fisheries 

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To date, we have tagged over 400 individuals with a combination of acoustic tags (Vemco/Innovasea) and pop-up satellite archival tags (Minipats; Wildlife Computers) and maintained an active acoustic array (peaking at nearly 100 receivers) between 2013 and 2021. As a result, we have amassed an extensive dataset on predator movement ecology and the associated biological and morphometric data from all individuals within the study.

 

Unfortunately, illegal, unreported and unregulated (IUU) fishing represents a major challenge to the MPA and its predator community. We have therefore also been working to assess the impact that IUU fishing is having on the ecology of the archipelago, how movement patterns of reef sharks are strongly linked to their vulnerability to illegal fishing activity, and the direct and indirect threats posed by regional fishing activity, such as drifting fish aggregating devices (dFADs). Collectively, our research is directly informing management and enforcement strategies within the MPA and helping to characterise the conservation and management role of large MPA for large marine animals.

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