Whale shark movements between atolls in the Maldives

Abstract

The Maldives is home to a large number of whale sharks, Rhincodon Typus. Much is known of the year round aggregation site in South Ari atoll, whose residents are protected by Marine Protected Area. Development of the citizen science network has enabled understandings of the distribution of the Maldives on a whole to be documented, and found that sharks are seen not only in Ari but across the island chains. However, movements in these areas are poorly understood. The aims of this therefore study were to identify sharks in other atolls, assess movement, and link this movement to environmental variables. The whale shark encounter data used in this database were collected by the Maldives Whale Shark Research Programme and citizen scientists spanning from 1992 to 2018. 13 environmental variables were modelled with sightings of moving sharks through subsets using Generalized Additive Models. 8 predictor variables were found to be significant, with 39.3% of variance explained by Oceanograhic variables atoll and distance to seamount while Temporal variables Time, month and year explained 21.1%. Indian Ocean Dipole Index, Sea Surface Temperature and chlorophyll-a combined accounted for only 2.85% of the variance. Whale sharks exhibited defined bi-annual movement between monsoons, and seasonal presence at all atolls other than South Ari. Seasonally alternating currents likely bring food resources distributed to different atolls that either become more or less suitable for whale sharks. Further research through satellite tagging is needed to confirm movements, and biomass samples carried out to quantify changes in prey species.