Effects of Depth and Marine Reserve Fishing Restrictions on the Structure of a Rocky Reef Fish Assemblage in the North-Western Mediterranean Sea

SUMMARY (1) A visual scuba diving census, in which abundance and size class structure of conspicuous fish species were determined, was used to assess the effects of depth and marine reserve fishing restrictions on the structure of a Mediterranean rocky reef fish assemblage by comparing communities at sites from two depth ranges inside and outside a marine reserve. (2) The total assemblage had thirty-five conspicuous species and was dominated by Labridae (thirteen spp.) and Sparidae (nine spp.). (3) Mean species richness (number of species) and diversity (Shannon) did not differ significantly between sites. (4) Ordination of abundance data showed that occurrence and relative abundance of species was affected by depth (deep samples separated completely from shallow samples) and marine reserve status (samples from the marine reserve were significantly separated from those taken at the same depth outside the reserve). (5) Samples from the same depth were similar, because the majority of species showed a preference for either deep or shallow areas. The known biology of several species indicated that feeding requirements may be responsible for depth preferences. (6) Samples from reserve sites had signficantly higher densities of fish species sought after and/or vulnerable to local fishing methods, than those from non-reserve sites of similar depth. (7) Size frequency distributions of vulnerable species at reserve sites generally had a larger modal size class than distributions from non-reserve sites. (8) The data suggest that reduced fishing pressure in the reserve has provided effective protection for species vulnerable to fishing.