Rachel is using animal-attached tagging technologies to investigate the behaviour and energetics of reef manta rays at D’Arros and St Joseph. Her project aims to develop a deeper understanding of habitat use at this important aggregation site. What are the mantas doing whilst they are here and what does this tell us about their ecological role in coral reef systems?
Growing up on the coast of Western Australia in Perth, I always had a love for and fascination with the natural environment, particularly the ocean. My parents were both environmentalists and because of this I was fortunate to grow up exploring remote places around the world. Some of my fondest memories revolve around these experiences. At the age of 12 I begged my parents to let me learn how to scuba dive, and it was being immersed in the marine environment that helped me solidify the sense of wonder and curiosity that has driven me to learn more about this...
To quantify the behaviour and activity regimes of free-swimming reef manta rays within a marine protected area at D’Arros Island, Seychelles, using novel biologging devices. We aim to understand the spatio-temporal patterns in time–energy budgets of the manta rays; gain insights into their functional ecology at coral reefs; and quantify the overlap of key behaviours within the marine protected area.
The reef manta ray is a threatened species, yet we have no detailed understanding of how much time and energy it spends on key life-history processes. The factors that determine behaviours and their costs are crucial to predict and mitigate how human disturbance, climate change and habitat alteration impact these rays. Isolated as it is, D’Arros Island offers a unique opportunity to gather important information about the energetics of reef manta rays within a relatively undisturbed area, thus providing an important global baseline. We also know little about what drives high rates of residency and site fidelity in manta rays. By identifying the physical and biological processes that influence the species’ movements and behaviour, as well as estimating the energetic costs underlying specific behaviour, this study will improve our ability to recognise critical habitats for reef manta rays and provide a broader understanding of what determines their movements and ecological role in coral reef systems in Seychelles and on a global scale.
The reef manta ray is a large mobulid ray with a tropical and subtropical distribution throughout much of the Indian and Pacific oceans. It is typically resident in productive near-shore environments, such as coral and rocky reefs of island groups, atolls and continental coastlines. Although individuals are capable of long-distance movements of up to 1,150 kilometres (715 miles), they seldom travel so far. There is low connectivity between widely separated sites and a high degree of residency, which makes the reef manta ray vulnerable to local depletion, which may lead to regional extinction.
Given the potential for reef manta rays to influence nutrient flow, their disappearance from aggregation sites may negatively affect local reefs. Whereas many reef-associated species forage over short distances within coral reefs, reef manta rays travel longer distances to feed on zooplankton communities offshore. This foraging behaviour, coupled with the rays’ residency at aggregation sites, may facilitate the transport and recycling of nutrients between isolated reefs and offshore environments, benefiting coral growth and productivity within these reef systems. Our current understanding of the feeding ecology of reef manta rays, however, has relied on indirect and/or passive measures of foraging behaviour. Fine-scale multi-sensor tag technology will enhance our knowledge.
The aggregation of reef manta rays at D’Arros Island provides an opportunity to document the behavioural and energetic baselines for the species, which are necessary to subsequently quantify anthropogenic threats. D’Arros is a significant aggregation site for reef manta rays and since 2013 has been the focus of a programme monitoring their movement patterns and foraging behaviour within the archipelago. Until now, it has not been possible to quantify the rays’ behavioural regimes at this site, but the development of biologging tags that can be mounted on wild animals without the need for capture has now made this possible. For the first time, we have the opportunity to better understand the drivers of behaviour and habitat use patterns of reef manta rays in the Seychelles, and the functional role that these rays may play in coral reef environments.
D’Arros and St Joseph represent an important aggregation site for the threatened reef manta ray. Body size is a key life history parameter that informs important aspects of species biology. Various techniques and methodologies are available for measuring animals in the wild. Two methods that have been applied to measure reef manta rays include stereo-video measurement and drone measurement. This study presents a critical comparison of the efficacy and applicability of these two established techniques for measuring reef manta rays and aims to establish which technique is most suitable for different research objectives.
Jeremy wants to understand when blue whales and other whales and dolphins visit Seychelles, and how many visit when they do. He investigates which factors, such as ocean currents and noise pollution, affect their presence and behaviour in these waters. To do this, he spends hours observing whales and dolphins from a boat, documenting their behaviour, where they move and what they do. He also uses their calls to determine when they arrive, whether they’re feeding or mating, and where they come from. This information can help identify new behaviours and important areas that need protection.
Nico is using acoustic telemetry and BRUVs around Seychelles to explore how reef sharks are using their reef homes. What are they eating? What prey is available? His project aims to explore what factors influence ideal habitats for sharks and will combine information from both pristine and degraded reefs to create a model to test this suitability. The point? To build on work by the Marine Futures Lab across the Indian Ocean and the Indo-Pacific and to help identify priority shark conservation areas.