Ningaloo whale sharks head in three directions

Whale shark and diverAn eight metre whale shark with a satellite tag attached at the base of its dorsal fin. The Australian Institute of Marine Science is examining the regional long-term movement patterns of whale sharks at Ningaloo Reef by tracking sharks with a variety of tags. (Photo: Rob Harcourt)

Each year from March to May, whale sharks aggregate on the continental shelf of the central Western Australian coast. At Ningaloo Reef, they swim close to the reef front, within a few kilometres of the shore and in water of less than 50 metres deep.

A tourist industry based on snorkelling with the sharks in this area has developed in the past 10 years. The Australian Institute of Marine Science is examining the regional long-term movement patterns of whale sharks at Ningaloo Reef by tracking sharks with a variety of tags.

Between 2005 and 2008, 19 data-collecting Argos satellite tags were deployed on whale sharks at Ningaloo. The tags transmit location, depth and temperature data to satellites when the tag aerial and switch break the surface. Estimates of location can be as precise as less than 150 m. The tags are embedded in a buoyant, hydrodynamic housing linked to a nylon coated stainless steel tether anchored to the side of a delron collar. The collar is fitted around the base of the first dorsal fin of the whale shark using a stainless steel underwater applicator.

Several of the tag deployments were of sufficient duration for the sharks to begin migrations away from Ningaloo to other areas of their range. These tracks revealed three general migration patterns where sharks moved:

1. north-west into the open Indian Ocean, some close to Christmas Island;
2. north towards Sumatra and Java and occasionally into Indonesian waters; or
3. north-east along the WA coast around the 200 m depth contour towards the Timor Sea.

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