Whale sharks have homing instincts

01 September 2017
Posted by Chris Smith.

While it might be the biggest fish in the sea, the whale shark, which can grow to more than 10 metres and weigh 20 tonnes, is surprisingly one of the least well understood. And reclassified recently as "endangered", the race is now on to understand more about these extraordinary animals if they to stand any chance of being conserved successfully.

This aim came a step closer this week with a new study from Ningaloo, Western Australia, which has helped to shed light on where whale sharks go, and may also be good news for tourism in the region.

Writing in the journal Diversity and Distributions, Sam Reynolds and her colleagues have obtained the first evidence that Ningaloo whale sharks have a homing instinct and, following forays over considerable distances, tend to repeatedly re-congregate in the area.

The team used satellite tags, which remained attached to the dorsal fins of the sharks for up to 9 months and periodically beamed back location coordinates whenever the 25 animals they were following surfaced. The average follow up lasted 90 days and provided the researchers with 100 or so data points to work with.

The animals, which were also photographed when the tags were first applied at Ningaloo Reef to aid later identification if they returned there, traveled an average of 2300 kilometres, and in one case over 6000 kilometres, during the follow up period. Most headed away from Ningaloo going north with one reaching Indonesia, but others went south, one as far as Perth.

That much was expected, because researchers had speculated that these animals show migratory tendencies and may even be circling the globe. However, what was less expected is that, rather like homing pigeons, the animals subsequently returned to Ningaloo within the year.

They also spent very little time during their excursions in any of the other marine protected areas along the Western Australia coastline. And as the researchers point out in the paper, when marine protected areas are planned migratory species are not taken into consideration and that perhaps telemetry data like that gathered in their study could be used in future to better inform conservation planning.

Northwestern western Australia is also undergoing significant oil and gas exploration works, meaning that shipping density is high in this area. And since whale sharks tend to spend large amounts of time close to the surface, they are particularly vulnerable to boat and propeller strikes.

There is some good news for the tourism industry, however, because, traditionally, only the first part of the year has been regarded as "whale shark season". The new data suggest that the whale sharks are present throughout the year but they move slightly further south later in the year. "It looks like Ningaloo Reef is an important area for whale sharks all year round. Whale shark season could last all year!" says study co-author Brad Norman.

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