The influence of El Niño Southern Oscillation on the population dynamics of oceanic manta rays in the Mexican Pacific

Oceanic manta rays Mobula birostris are declining globally due to fisheries. Past work has shown that movements and distributions of oceanic manta ray populations are sensitive to climatic fluctuations such as the El Niño Southern Oscillation. The Revillagigedo National Park (RNP), Mexico, is a well-known aggregation site for oceanic manta rays. However, published baseline data on population structure and dynamics, and the influence of oceanographic variables on the abundance of oceanic manta rays in the region are lacking. We used 2015–2019 photo-identification data to describe baseline demographic characteristics of this population and to evaluate the influence of environmental factors on population dynamics. A significant sex bias was found with a female:male ratio of 1.4:1. Mark-recapture (MR) was used to estimate monthly abundance and provided the first superpopulation size estimate of 1172 (± 90), representing all individuals using the RNP during the survey period. The MR analysis suggests a significant relationship between the multivariate ENSO index and monthly survival probabilities, and chlorophyll-a as a driver of recruitment in surveyed dive sites. These findings provide a baseline to support effective conservation and management plans for this endangered species in the Mexican Pacific.