Occupancy of acoustically tagged oceanic manta rays, Mobula birostris, in Bahia de Banderas, Mexico

Abstract

AbstractThe oceanic manta ray (Mobula birostris) is an endangered species commonly seen at oceanic islands and seamounts; however, seasonal aggregations have been described in highly productive, coastal areas. Oceanic manta rays are found in high numbers seasonally in Bahía de Banderas, Mexico, a unique nearshore aggregation site for the species. We used acoustic telemetry to examine the influence of environmental variables on the occurrence of 66 tagged oceanic manta rays over a seven-year period from 2015 to 2021. Seasonal trends in oceanic manta ray occurrence showed a peak in detections from January to March, and another peak from May to early October. Oceanic manta rays were present when the temperature ranged between 25 °C and 29 °C, the southward wind speeds ranged between 3 and 5 m s–1, the westward wind speed between 2.5 and 4.5 m s–1. Furthermore, oceanic manta rays’ presence was higher at high and low tides and when Chlorophyll-a values ranged between 2.5 and 7 mg m3-1. Results also suggest that El Niño Southern Oscillation (ENSO) had a strong effect on oceanic manta ray presence in the bay, which is consistent with previous studies. The detections of oceanic manta rays in the south of the bay, were greater in the morning hours, suggesting that during the night they may move to deeper waters, similar to other reported studies of manta and devil rays. Our model suggested a tag retention time of 300 days. This study serves as a baseline for future management plans for the species to minimize impacts on this population from human activities occurring in close proximity to oceanic manta ray aggregation sites.