Blacktip Sharks: Breeding Females Find Year-Round Sanctuary In Australia Bay

A new study from James Cook University revealed an uncharacteristic behavior of female blacktip reef sharks living in Cockle Bay near Townsville, Australia. Curiously, researchers found moms and their young stay close to shore for longer periods of time, while males join them only during breeding season. While this was unexpected, researchers say their discovery highlights the importance of conservation along coastal areas. 

"Adult female sharks are supposed to come in seasonally to give birth, and then leave," Dr. Andrew Chin, lead author of the study, explained in a news release. "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." 

Over 100 sharks were tagged for their study, 28 of which were fitted with tracking tags to follow their movement patterns over a period of two years.

"Neonates and juveniles were short-term residents; adult females were long-term residents and preliminary data suggest that adult males were vagrants, arriving in the area only to breed," Dr. Chin added in the university's release. "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 rubble flats nearby."

This is the first study to show that young reef Pacific sharks grow up alongside breeding adult females and only transition to reefs offshore when they reach their teenage years. What remains somewhat of a mystery, however, is why the sharks appear to have a particular attachment to Cockle Bay. 

"Blacktip reef sharks from Cockle Bay didn't use them [seagrasses and mangroves]," Dr. Chin noted. "Some of them even stayed in the bay as a Category 5 cyclone approached while all the other sharks in the area left."

Cockle Bay lies within a conservation park where commercial net fishing is prohibited. It is believed that the sharks may remain close to this area because it provides good protection to resident breeding females.

"While blacktip reef sharks aren't prime target species like barra or trout, if recreational fishers start keeping too many sharks from there, it could have wider effects," Dr. Chin concluded. "Our study highlights the importance of protecting coastal habitats, and also managing these breeding grounds to ensure that adult females are looked after." 

Their study was recently published in the Marine Ecology Progress Series.

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