bull sharks

Protecting migrating shark species isn’t always easy

Publication Specs

Title: Conservation challenges of sharks with continental scale migrations

Authors: Michelle R. Heupel, Colin A. Simpfendorfer, Mario Espinoza, Amy F. Smoothey, Andrew Tobin and Victor Peddemors

Journal: Frontiers in Marine Science

Year: 2015

It’s no surprise to anyone that sharks can move. What may be surprising is that some shark species can move thousands of kilometers, traveling across multiple jurisdictions. When sharks swim across state, national, and international boundaries they are exposing themselves to varying levels of threats and protections. In order for conservation measures to be effective for mobile species, knowledge of the scale of movement is required.

Bull sharks are no strangers to long-distance movements, being known to travel hundreds of kilometers. On the Australian East coast, researchers studied bull shark movements across two state jurisdictions: Queensland (QLD) and New South Wales (NSW) using acoustic telemetry. Tracking devices were surgically inserted into 114 bull sharks, which then transmitted their signals to fixed receivers. When a tagged shark swam past the receiver, data on that individual was stored and later retrieved.  

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On average, the bull sharks were found to travel 1194km with no evidence of individuals making movements based on the time of year. The sharks were detected on multiple receivers at various sites, which is evidence that these sharks are connecting temperate and tropical systems while also crossing state boundaries.

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Larger juveniles and adults were found to swim the furthest, with multiple hypotheses for this behavior:

  • The shift in diet from juvenile to adulthood
  • The need to reduce competition for food
  • To avoid eating their own kin
  • Less tolerance for nearshore freshwater
  • A combination of all of the above

Since bull sharks are frequently moving along the eastern coast of Australia, current marine protected area zoning may have limited benefits for this species. Managers face complex challenges when making conservation decisions that affect highly mobile shark species. This study highlights the need for jurisdictional cooperation between QLD and NSW that would lead to effective marine protected area zoning, which could include movement corridors for bull sharks. Nonetheless, managers face difficult decisions in terms of negotiation and coordination with different governments when trying to protect species that move across state, national, and international boundaries. Studies like this one will improve our knowledge of shark movements in order to facilitate the decision-making process that will lead to effective conservation measures.