C and N stable isotope ratios in fishes from marine protected areas and areas open to fishing

Here, we assess whether fishery exploitation affects the trophic structure
of carnivorous fishes. We censused fishes and analysed the stable isotope
ratios of C and N of species targeted by fishermen in areas open to
fishing and marine protected areas in the Mediterranean Sea and the
north-eastern Atlantic Ocean. Results demonstrated a major impact of
fishing on the biomass and the size structure of nektobenthic carnivorous
fishes. However, those changes did not modify the diversity of the trophic
resources used by the assemblage, the pattern of resource partitioning
between species or the degree of trophic redundancy. These results add to
recent evidence suggesting that marine protected areas implemented in
fished seascapes may fail to restore the original structure of the food
webs that once existed in pre-fished ecosystems, because regional
decimation and extinction of highly mobile predators prevents recovering
the original diversity of predators at local scales, even at no-take
areas. If so, more strict local fishing regulations are unlikely to
restore the original diversity of high trophic level carnivores and
restoration goals should be reframed in terms of an objective that is less
unrealistic than restoring the pre-fished condition while still recovering
aspects of the historical trophic structure.