Non-lethal efforts to deter shark predation of Hawaiian monk seal pups

Published on 14. September 2012

Non-lethal efforts to deter shark predation of Hawaiian monk seal pups

Kathleen S. Gobush and Shawn C. Farry


More than a decade of shark predation on nursing and newly weaned pups of the endangered Hawaiian monk seal (Monachus schauinslandi) has significantly contributed to a steep decline of the French Frigate Shoals (FFS) subpopulation.
In an effort to develop non-lethal methods of mitigating predation, the feasibility of deploying potential shark deterrents at FFS was examined, and then tests were done to see if any of the successfully deployed devices or a continuous human presence deters shark predation of monk seal pups.
During the feasibility trial, an underwater acoustic playback and a moored boat performed without issue. A float array proved hazardous to non-target wildlife and electronic diver devices functioned poorly; both were omitted from further experimentation.
The number of shark sightings and predation incidents at two pupping islets was compared across two experimental treatments: (1) acoustic playback and a moored boat, and (2) continuous human presence, versus a control. Sharks were sighted with a remote camera system; predation incidents were evident from bite wounds or the disappearance of pups.
Observed shark activity was rare (12 sightings on video and six predation incidents) but similar to recent years. The number of shark sightings and predation incidents did not differ significantly between the two treatments and the control.
The relative scarcity of shark activity in the shallows around the pupping islets made detecting a treatment effect challenging. Sharks’ wariness to humans is probably variable, unpredictable, possibly individualistic and unreliable at FFS. The acoustic playback as a deterrent could benefit from further testing and development. Other non-lethal or lethal approaches for mitigating predation should be investigated to protect monk seal pups at FFS.

Aquatic Conserv: Mar. Freshw. Ecosyst.. doi: 10.1002/aqc.2272



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