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Abstract

A large aggregation of whale sharks in the central part of the Arabian/Persian Gulf has recently been documented by the Qatar Whale Shark Research project. Observations made by offshore workers have indicated a continuous presence of whale sharks close to platforms in the Al Shaheen oil field during the summer months. It has been established that the sharks come here to feed on fish eggs of the Mackerel tuna, . The Al Shaheen location is characterized by numerous offshore platforms that could attract the spawning Mackerel tuna and thereby influence the numbers and distribution of whale sharks in the area. Understanding the movement and residency patterns of whale sharks is critical for their management, particularly in an offshore oil field. In the period from 2012–2015 a total of 104 whale sharks were fitted with acoustic V16 tags. The sharks were all tagged in the Al Shaheen oil field during the aggregation period from May to September and ranged in size from 4 to 10 meters TL. The movement pattern of sharks within the Al Shaheen field was monitored using an array of up to 15 VR2W receivers placed a minimum of 4 km apart. The receivers were placed on the seabed at different distances from selected offshore installations and recovered using remotely activated releases. Of the 104 tagged sharks, 102 were detected by the deployed receivers during the study period. The maximum detection distance was estimated to be between 500–1000 m from the receiver. More than 99% of the detections occurred between the months of April–September. Average annual residence time in the Al Shaheen area was 38.5 days (±27.5 SD) with some sharks showing a continued presence during the entire April–September period. The results indicate that the whale sharks are almost only present in the Al Shaheen area during the April–September period, confirming the visual observations made by workers on the offshore installations. Aggregations, sometimes numbering more than 100 individuals, have only been observed while the whale sharks were feeding on Mackerel tuna spawn. The long residence time indicates that the Al Shaheen area is a highly important feeding ground. The sharks showed a high affinity for the same platforms throughout the study period, while their presence was only rarely recorded at other platform locations. This could indicate that the Mackerel tuna are spawning in a confined location within the study area and that the whale shark distribution within Al Shaheen is strongly associated to the spawning site and the prevailing currents. The platforms themselves may concentrate whale shark presence in the spawning area, but their full importance for the behavior of whale sharks is still to be determined. Mitigating measures have been established in order to minimize potential impacts on whale sharks related to offshore activities.

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/content/papers/10.5339/qproc.2016.iwsc4.6
2016-05-15
2019-10-16
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