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Research expedition to St Joseph’s Atoll

By Emily Moxham, 17th May 2015

I currently find myself on a research expedition to the St Joseph Atoll in Seychelles. This is my second trip to St Joseph in as many years. In 2014, our research team initiated a research project on the movement behaviour of stingrays in the atoll. The current month-long fieldtrip will see the research team tagging more stingrays, but we will also be starting a new project on bonefish and permit, which are abundant inhabitants of the atoll and important recreational fishery species around the world.

The overall aim of this research is to answer the where, when and why questions about fish movements, which is essential for effective conservation and management of our study species, as well as of the atoll environment they inhabit. Each fish is surgically equipped (tagged) with an acoustic transmitter that produces a unique signal every couple of minutes. The transmitted signal is then detected by acoustic receivers (listening stations) that are deployed in and around the atoll. Each receiver, with a known position, recognises the unique identification code of each tagged fish and stores the date and time when it swims past. Once all the data stored on the receivers is downloaded, we will be able to map the daily, monthly, seasonal and multi-year whereabouts of each tagged fish. Effectively this will allow us to answer the where and when questions about their behaviour. This is very important because atoll environments are strongly influenced by the tides, which expose vast sand flats at low tide and offer huge feeding opportunities during high tide. The data will reveal when the tagged fishes utilise the sand flats and atoll lagoon in relation to time of day and phase of tide. Fishes do not only exhibit daily and tidal movement patterns, but also lunar and seasonal patterns that, if detected, will shed light on their reproductive biology.

The long-term data will hopefully provide information on when and where the tagged fish breed. For example, studies conducted on bonefish elsewhere in the world have shown that they leave atoll environments on new or full moon to spawn. Finally, we will also learn from the multiple-year data whether the bonefish and stingrays exhibit long-term residency to St Joseph, which is important in light of the proposed marine reserve status of the atoll and neighbouring D’Arros Island.

In addition to movement behaviour, the research team will study the species’ dietary habits, which will collectively provide new information on the trophic ecology and dynamics of these dominant fish species that utilise the intertidal flats of the St Joseph Atoll.

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