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Rountree, R.A. 1987.
Ecology of the association of fishes with fish aggregation devices (FADs): Importance of structural complexity, with a discussion of the association of fishes with drift materials. MS Thesis, College of Charleston, South Carolina. U.M.I. #MAI-1333393. 176 p
The hypothesis that the standing crop of fishes associated with a FAD is a function of the degree of protection provided by the structure was tested by comparing recruitment to three types of mid-water FADS. Since the structural complexity of the FAD was considered to be directly related to the shelter available to the associated fishes, three FAD types with increasing orders of structural complexity were used as treatments. Each treatment was replicated six times and the eighteen FADs were deployed at 30 m intervals along a rope grid in 14 m of water off Charleston, South Carolina. A total of 20 families and 36 species of fishes were observed at 121 stations censused in eight surveys from May through November 1985. The fauna associated with the FADs was very similar to published reports of fauna associated with Sargassum spp. and jellyfish, suggesting similar origins and causes. Decapterus punctatus was the most frequently occurring (70) and abundant species (X = 576 individuals/station). Other common species included Caranx crysos, Diplectrum formosum, Caranx bartholomaei, Centropristis striata and Monacanthus hispidus. The number of species (X = 3.8), total number of individuals (X = 592) and number of Decapterus punctatus per station were significantly different among FAD type treatments (P = 0.0087, 0.0163, 0.0467, respectively). Fewer species of demersal fishes were attracted to concrete anchors after the loss of the FAD than to anchors with the FAD intact, suggesting a correlation of some demersal species with the occurrence of pelagic fishes at the FADS. Observations of fish behavior and quantitative analysis of spatial distributions of fishes around the structures revealed that Decapterus punctatus occupied a position progressively farther up current of the FAD with increasing number of individuals per school. Decapterus punctatus made direct use of shelter only when present in small numbers or when disturbed by diver activity. I propose a model suggesting a visual mechanism that provides an advantage to schooling fish in avoiding predator attacks, and that Decapterus punctatus takes up a position around a FAD which enhances the school's ability to detect and avoid approaching predators.
Additionally, associations with drifting objects may allow a prey fish, which has habituated to an object, to escape predation by capitalizing on a reflexive avoidance of the object by a pursuing predator. Implications of the results and conclusions drawn from this study demonstrate the feasibility and value of using designed and replicated artificial reef structures in experimental designs for the in situ study of marine habitat ecology. The importance of the interpretation of data obtained from such studies in light of behavioral observations is emphasized.
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