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20.02.2015 00:53 Age: 3 yrs

Long-range movement of bull sharks revealed

This discovery was facilitated by use of data from the network of acoustic receivers around the coast of Australia deployed as part of the IMOS Animal Tagging and Monitoring Facility.

Bull sharks Image credit: Colin Simpfendorfer, James Cook University

Connectivity plot indicating moves of individual bull sharks between acoustic receiver arrays. Line thickness represents density of movements. The number of sharks detected by location are indicated on the inset bar graph. Image credit: Heupel et al.

The long-range movements of species can be hard to capture. Technology is advancing to help solve these issues, but sometimes it is a matter of being in the right place at the right time.

A collaboration between the Australian Institute of Marine Science, James Cook University and NSW Department of Fisheries has revealed previously unknown linkages in coastal bull shark populations. This discovery was facilitated by use of data from the network of acoustic receivers around the coast of Australia deployed as part of the IMOS Animal Tagging and Monitoring Facility

In two separate research projects 39 bull sharks were fitted with acoustic transmitters in the reefs offshore from Townsville and 75 individuals were similarly tagged in Sydney Harbour and the Clarence River. Approximately half of the individuals tagged in NSW were recorded on receivers in Qld, including the region offshore from Townsville.

Individuals were detected on various acoustic receiver arrays along the Qld coast and at installations offshore in regions such as the Capricorn Bunker Group. Shared detection data from individuals that made large moves has provided a unique opportunity to examine long range movements of bull sharks along the east coast. This would not have been possible without collaboration and connections within the IMOS community. 

In contrast, sharks tagged in reef regions were less likely to move south. Only one individual released in Qld was detected on NSW arrays. Approximately 25% of reef tagged individuals, however, moved further north beyond the Townsville region suggested broader movements are also likely in this segment in the population, just not in a southerly direction.

Broad scale movement of large predators is directly relevant to both management and conservation efforts. Crossing of jurisdictional boundaries, both national and international, could have significant consequences for the status of populations. Further data is needed on key species to understand the dynamics of these movements and implications for management.

These findings indicates direct linkages between what may have been considered separate populations and suggests coral reef regions may play a key role in the ecology of bull sharks on the east coast of Australia. The results also clearly demonstrate the power of a coordinated continental scale acoustic network and the opportunities for discovery and exploration it can provide.

For more information about this research please see the recent publication in Frontiers in Marine Science:

Heupel M, Simpfendorfer C, Espinoza M, Smoothey A, Tobin A and Peddemors V (2015). Conservation challenges of sharks with continental scale migrations. Front. Mar. Sci. 2:12. doi: 10.3389/fmars.2015.00012

News item written by Michelle Heupel.