Trophic niche width collapse in coral reef-associated predators: An unforeseen consequence of fishing

The impacts of fishing on the trophic relationships of species in complex communities have proven difficult to assess using traditional methods such as stomach contents analysis and underwater visual census techniques. We used a stable isotope approach to elucidate the effects of fishing on the niche widths of multiple coral reef fish species along a gradient of fishing pressure in the Bahamas.  ¹³C-¹⁵N bi-plots reveal that the trophic niche widths of large- and medium-sized piscivores collapsed by 48% and 31%, respectively, from low to high fishing pressure. Large piscivores inhabiting lightly fished reefs also fed at a significantly higher trophic level than their conspecifics on heavily fished reefs. The complete lack of overlap observed in the isotope-based trophic niche widths of this guild suggests that the trophic role of large predatory fishes may be altered as a consequence of heavy fishing pressure. Our results reinforce the need for ecosystem-based management strategies which address the wider consequences of extractive fisheries.