You might think, perhaps, that losing track of something as enormous as a whale shark would be difficult.
Surprisingly, however, that is what has been happening for many years: whale sharks (Rhincodon typus) known to inhabit waters off the coast of northern Western Australia in autumn and winter have gone missing during spring and summer, whereabouts unknown.
New research from the University of Queensland and the non-profit organisation Ecocean, using telemetry collected from 29 tagged sharks within 2,633 sq km Ningaloo Marine Park, appears to have solved the mystery. The whale sharks were there all the time – or much of it, anyway.
“Our tagged whale sharks were tracked returning to Ningaloo Reef throughout the year, and our modelling suggests that it provides suitable habitat for them year-round,” says Ecocean marine biologist Samantha Reynolds.
The study by Reynolds and her colleagues, published in the journal Diversity and Distributions, reveals that during spring and summer the sharks travel up to 1,500 km from their tagging locations in Ningaloo, before returning again.
The sharks did not stay away from the marine park for entire seasons, returning periodically. Away from the park, they were tracked swimming into the Timor Sea, as well as all the way to the coast of Java, and out into the Indian Ocean towards Christmas island.
The data was collected between 2010 to 2015. The findings have implications for the eco-tourism industry that operates in the marine park, as the chance to encounter a 21-tonne, 12-metre whale shark is major driver of visitor numbers to the park.
“The eco-tourism industry takes visitors swimming with whale sharks at Ningaloo Reef in autumn and winter, but until now the creatures’ whereabouts at other times of the year has remained a mystery,” Reynolds says. “Whale shark season at Ningaloo could last all year.”
The results also provide firm data on which to base decisions about the management of the species, which is listed as endangered.
Much of the area favoured by the sharks beyond the confines of Ningaloo confers no protective status, and some areas are impacted by industrial pollution and shipping traffic.
“Our study highlights the need for international co-operation for the protection of whale sharks,” Reynolds says.