Bertarelli-Annual-Report-2024-FULL - Flipbook - Page 39
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Marine Science 2024
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Spatial and Temporal
Variations in Reef Manta
Ray (Mobula alfredi)
Meso-Scale Habitat Use
and the Implications for
Conservation
Harris, J.L., Hosegood, P., Embling, C.B., Williamson,
B.J., Stevens, G.M. (2024). Aquatic Conservation
https://doi.org/10.1002/aqc.4089
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Reef manta ray (Mobula alfredi) populations are small and
often isolated, producing very low numbers of offspring.
While the Chagos Archipelago is a large no-take marine
protected area, illegal, unreported and unregulated fishing
poses a substantial threat to the reef manta rays that
live there. A study of 42 reef manta rays was conducted
at a known hotspot - Egmont Atoll - between 2019 and
2022 using passive acoustic telemetry and modelled
environmental data. These rays displayed the highest
levels of residency ever reported (77%), with prolonged
absences (>two months) limited to seven individuals.
Egmont Atoll was used by mantas year-round, with activity
peaks during the southeast monsoon (April – November),
particularly at sites on the southwest, while sites on
the northwest were predominately frequented in the
northwest monsoon (December–March). Mantas were
found to be reliant on Egmont Atoll for food, particularly
when the Indian Ocean Dipole was in a positive phase with
a greater mixed layer depth, associated with less available
plankton in the Indian Ocean. These findings highlight the
importance of ensuring the protection of Egmont Atoll.
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