Use of aerial surveys for assessing abundance of the whale shark (Rhincodon typus) and the giant manta (Mobula birostris) in the northern Caribbean Sea off Mexico

The whale shark (Rhincodon typus) and the giant manta (Mobula birostris) are migratory species that occasionally occur in the same foraging habitat. Both planktotrophic elasmo-branch species can be found seasonally in aggregations from 2 individuals to hundreds of animals in the northern Caribbean Sea off the Yucatan Peninsula of Mexico because of the abundance of food in this area. The aim of this study was to assess the distribution and abundance of the whale shark and giant manta by conducting aerial surveys from May through September during 2016-2018. A total of 953 whale sharks and 466 giant mantas were sighted during 17 aerial surveys. The largest groups of whale sharks and giant mantas were recorded in July 2017 and September 2016, respectively. Aerial survey data were used to estimate the mean density of each species in this aggregation area: 14 whale sharks/100 km(2) and 8 giant mantas/100 km(2). These values were used to estimate the spatiotemporal variability of the number of whale sharks and giant mantas feeding at the surface. The results of this study indicate that both species were not distributed homogeneously in the assessed area, a situation that often interferes with the implementation of suitable strategies for managing tourist activities.