In a surprise result, James Cook University scientists have found female blacktip reef sharks and their young stay close to shore over long time periods, with adult males only appearing during the breeding season. The researchers also discovered the sharks had a mysterious attraction to a specific bay near Townsville. 

 

Lead author, JCU's Dr Andrew Chin, said the data from an area adjacent to the city wasn't what they expected and points to an even more important role for coastal¹ areas than previously² thought. 

 

"Adult female sharks are supposed to come in seasonally³ to give birth, and then leave. But these adult females seem to remain in these areas all year round, and give birth there. The young grow up in muddy coastal bays using seagrass beds and mangroves before migrating." 

 

The team tagged over 100 sharks and fitted 28 sharks with tracking tags to follow their movement patterns for more than two years. 

 

"Neonates and juveniles⁴ were short-term residents; adult females were long-term residents and preliminary data suggest that adult males were vagrants⁵, arriving in the area only to breed," said Dr Chin. 

 

He said the study was the first in the Pacific to show that young reef sharks grow up alongside breeding adult females, using coastal habitats like seagrasses and mangroves. When they reach teenage years, they move to reefs offshore⁶. But their particular attachment⁷ to Cockle Bay on the south side of Magnetic Island remained a puzzle. 

 

"It doesn't appear to be linked to the availability of specific habitat types. There are extensive areas of mangroves and mudflats and fringing reef habitat, sand, mud and rubble⁸ flats nearby. But the blacktip reef sharks from Cockle Bay didn't use them. Some of them even stayed in the bay as a Category 5 cyclone⁹ approached while all the other sharks in the area left."

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