Shark overfishing may initiate trophic cascades on reefs via predatory and competitive release. To explore the influence of sharks on fish assemblages, I take advantage of a "natural" experiment created in northwestem Australia by centuries of targeted shark fishing at the Scott Reefs, contrasted with a relatively pristine but otherwise similar reef system called the Rowley Shoals. Methods include stereo-Baited Remote Underwater Video Stations, stereo-Diver Operated Video Stations and stable isotope, otolith, gut content and morphometric analyses. Declines in shark abundance were associated with changes in fish assemblages as follows: (a) increased abundance and biomass of prey size classes, (b) altered trophic position and niche width (c) altered growth rate, (d) shifts in diet from lower-quality, less risky food items towards riskier, more profitable items and (e) improved condition. The findings suggest that sharks regulate reefs via predation and competition and that conservation of these declining predators is therefore paramount.
|Qualification||Doctor of Philosophy|
|Award date||1 Aug 2016|
|Publication status||Unpublished - 2016|