The researchers tagged 21 tiger sharks caught in longlines during the course of the experiment. The sharks were hooked by the jaw using circle hooks as oppose to J-hooks - a method which has been previously proven to improve survival rates post-release. After the sharks were released, their movements were monitored via satellite. Most of the sharks caught were released in good health and none of the individuals died within 30 days of release, indicating that this species could be robust enough to successfully survive catch and release from longline circle hooks when caught as bycatch. This could be particularly important in this region of Brazil owing to the fact that all the sharks caught in this study were juveniles and therefore had no opportunity to reproduce. The authors also noted that the fishing pressure on the local shark population in this region was particularly high as artisanal fishermen in neighbouring waters fishing with gillnets and reported a much higher mortality rate for tiger sharks than reported from this study using longline circle hooks.
Interestingly, the researchers also discovered that tiger sharks released after capture tended to move into deeper water and did not return to the same area where they were captured for a considerable time. This suggests that these catch and release methods could be employed to successfully relocate problem tiger sharks in the area - a strategy which would be preferable to culling.
Other studies have predicted that tiger sharks are a keystone species in many ecosystems, and the removal of this apex predator would cause a great deal of disturbance in the ecosystems they are associated with. Therefore effective management strategies to minimise the impact of the fishing industry on tiger sharks are essential.
Sharks, along with other marine animals, are often caught unintentionally by the fishing industry as bycatch and estimates suggest that the bulk of this is ascribed to longline fisheries. The fact that tiger sharks could survive catch and release - at least if circle hooks are used for the capture - could be used to facilitate the effective management of longline fisheries with regards to shark conservation.
André S. Afonso, Fábio H.V. Hazin, Post-release survival and behavior and exposure to fisheries in juvenile tiger sharks, Galeocerdo cuvier, from the South Atlantic, Journal of Experimental Marine Biology and Ecology, Volume 454, May 2014, Pages 55-62
Link to the paper
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