Species-area relationships as indicators of human impacts on demersal fish communities

Aim: The relationship between number of species and area is a well-known macro-ecological property that can be used as an indicator of human impact on natural communities. This relationship can be described by species-area relationships. We explored the application of species-area relationships to data sets of bottom trawl surveys to determine their ability to capture fishinginduced changes in demersal fish communities. Location: Australia. Methods: We performed numerical simulations to investigate whether species-area relationship was sensitive to changes in community properties, such as richness, species abundances and spatial distribution. Then, we analysed a data set of bottom trawl surveys carried out in south-east Australia spanning 20 years. These data provided information on demersal fish communities at different stages of fishing exploitation. We built species-area relationships along spatial and temporal gradients of community exploitation and used the rate of species accumulation to characterize community structure. Linear mixed effects (LME) models were used to quantify the effect of fishing exploitation on species accumulation rates, while controlling for environmental and sampling factors. Results: Numerical simulations showed that species-area relationships can capture changes in community properties. Observed species accumulation rate decreased with increasing exploitation and was sensitive to environmental variation along a latitudinal and depth gradient and to changes in sampling. Main conclusions: Species-area relationships applied to trawl survey data can capture fishing-induced changes in the structure of demersal fish communities. We propose that species-area relationships can be used to inform on the status of demersal fish communities and aid community monitoring. If applied to data sets of bottom trawl surveys available world-wide, species-area relationships could be used to rank demersal fish communities for their level of exploitation.