Fish responses to increasing distance from artificial reefs on the Southeastern Brazilian Coast

Abstract

Artificial reefs have been deployed worldwide in shallow marine environments to enhance attraction and capture of fish, but, despite their potential as a fishery management option, few studies addressed whether fish assemblages will change with distance from a reef. We experimentally assessed the relationship between fish abundance and richness to increased distance (0, 25, 100, and 300 m) to reef balls deployed on a flat and homogeneous bottom, 9-m deep, on the north coast of Rio de Janeiro, Southeastern Brazil. A total of thirty fish species was associated with the reefs and the variation in species composition with sampling period or technique did not account for changes in fish assemblages with reef distance. Fish abundance and richness were significantly greater at the nearest distances (0 m and 50 m) to the reefs than at 300 m, but while the first dependent variable decreased exponentially with reef distance the later diminished linearly. Fish responses to reef distance were clearly species-specific and the tomtate ( Haemulon aurolineatum — the dominant species that probably used the reefs for shelter purposes) strongly influenced the exponential decreasing pattern found for the total number of fishes and abundance of Haemulidae. The abundance of the close congener Haemulon steindachneri, and of Chaetodon striatus, Serranus flaviventris and serranid species as a group also decreased, but linearly, with reef distance, probably related to variation in home-range. Acanthurus chirurgus and Scorpaena isthmensis decreased linearly in number with reef distance, probably due to feeding rather than refuge purposes. The abundance of Isopisthus parvipinnis tended to increase with reef distance, suggesting that artificial reefs might be unprofitable for those species less dependent on clear water or structurally complex habitats to obtain refuge or food. Overall, our study indicates that artificial reefs are a promising management tool to enhance fish capture in the oligotrophic waters and structureless bottoms of the north coast of Rio de Janeiro, but with varied rates of success, depending on the target species and fishing distance from the reefs.