Wild fish aggregations around fish farms in the Gulf of Aqaba, Red Sea: implications for fisheries management and conservation

A Özgül,D Angel

doi:10.3354/aei00076

Abstract

Fish farm structures attract a variety of fish species by providing solid structure, and 'free meals' in the form of uneaten feed and feces that fall from the cages. In this study, we com- pared the composition and abundances of wild fish populations around 2 fish farms in the Red Sea and at nearby reference locations. Fish assemblages were evaluated by SCUBA divers carrying out rapid visual censuses in August, September and October 2007. A total of 87 238 fishes, repre- senting 39 species and 25 families and a number of trophic levels, were observed. Overall, the abundance, biomass, and diversity of wild fish were much greater at the sea cages than at the open-water reference sites, at both fish farms. It is noteworthy that 35 out of the 39 species observed at the farms were juveniles and adults of coral-reef fish species. This finding is especially interesting, considering that the nearest coral reefs were >4 km away and reef fishes generally have small home ranges, typically <1 km. Among these, the Carangidae (5 species), Sparidae (3 species), and Pomacentridae (3 species) contributed the most to species richness. In light of strong fishing pressures in many areas, the large populations of wild fishes at the fish farms, the high availability of nourishment from artificial food pellets, and restrictions on fishing within farm lease areas, we suggest that coastal net-cage fish farms may serve as small marine protected areas.

Highlights

Since the development of modern sea-cage aquaculture in the early 1980s, the number of net-cage fish farms has increased rapidly throughout the coastal areas of the world (Theodorou 1999, Ferlin & La Croix 2000, Sanchez-Mata & Mora 2000, Beveridge 2004, Halwart et al 2007, Bostock et al 2010)
Natural and artificial fish aggregation devices (FADs) in the marine environment are widely recognized for their capacity to attract pelagic fishes
Aquaculture facilities in the marine environment that serve as FADs show characteristics of healthy artificial reefs, and as such may help improve ecosystem and aquaculture management strategies (Costa-Pierce & Bridger 2002, Alston et al 2006, Benetti et al 2006)

Summary

INTRODUCTION

Since the development of modern sea-cage aquaculture in the early 1980s, the number of net-cage fish farms has increased rapidly throughout the coastal areas of the world (Theodorou 1999, Ferlin & La Croix 2000, Sanchez-Mata & Mora 2000, Beveridge 2004, Halwart et al 2007, Bostock et al 2010). Natural and artificial fish aggregation devices (FADs) in the marine environment are widely recognized for their capacity to attract pelagic fishes Sea-cage fish farms attract wild fish by providing structure in the pelagic environment, and uneaten feed and feces that fall through the cages may enhance the attractive effect (Phillips et al 1985, Bjordal & Skar 1992, Dempster et al 2002). We evaluated species composition and total aggregated abundance and biomass of wild fish at 2 fish farms in the Red Sea and at reference locations in an effort to describe and understand the role of fish farms in structuring the wild fish assemblage in tropical environments

MATERIALS AND METHODS

RESULTS

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DISCUSSION