Whale shark residency and small-scale movements around oil and gas platforms in Qatar

Abstract

AbstractArtificial structures in the ocean can influence the movements and residency of migratory fishes. Whale sharks seasonally aggregate near oil and gas platforms in Qatar to feed on fish spawn, creating one of the largest aggregations for the species. We used passive acoustic telemetry to examine their fine-scale movements, residency, and seasonality and investigate whether the platforms influence their habitat use in the area. Tags had a mean retention of 161 ±186 SD days and 32 of the 117 tags were recorded in multiple seasons in the acoustic array (21 stations). Most detections were recorded during the season that was established with other methods from May to September, confirming that this whale shark aggregation is seasonal. Whale sharks stayed up to 77 consecutive days in the array (mean = 16 ± 12.51 days) and had a mean residency index Rmaxof 0.31, highlighting the importance of this site to their ecology. While most detections were made at a receiver near a platform, other platforms had few detections and the distance from the centre of the aggregation was the main explanatory variable in a GLM, indicating that the platforms do not influence the whale shark’s habitat use. Instead, they moved with the current during the morning, when they feed on fish eggs at the surface which also float with the current, and swam against the current in the late afternoon and at night to be at the presumed fish spawning site again in the early morning. Our results highlight the importance of this small feeding area for whale sharks which face a high threat level in the region.