Effects of anti-trawling artificial reefs on ecological indicators of inner shelf fish and invertebrate communities in the Cantabrian Sea (southern Bay of Biscay)

The analyses presented in this paper provide evidence that several community metrics and indicators of the inner shelf community in the Cantabrian Sea show response to placement of anti-trawling reefs. Total biomass, species richness, and to a lesser extent, maximum length and percentage of large fish, were sensitive to exclusion of trawling. Density, diversity and average trophic level did not show this sensitivity. The main species profiting from trawl exclusion were seabreams (Sparidae), catsharks and skates (Elasmobranchii), red mullets (Mullidae), gurnards (Triglidae) and John Dory (Zeus faber). Conversely, the main fishery target species (hake, anglerfish and megrim) showed a progressive decrease in abundance during the study period, a pattern which was also shown by their total stock biomass in the totality of the shelf area. Sea urchins, cephalopods and gastropods also increased in relative abundance with trawl exclusion. Reef age was identified as a key factor in reef development. After reef deployments, two periods were identified: (1) a recovery period, in which total biomass increased, mainly as a consequence of the increase in generalist species (e.g. catsharks); and (2) a consolidation period, during which biomass increased again, mainly as a consequence of an increase in specialized stenoic species (e.g. sparids), while biomass of generalist species remained constant or declined.