848 



Fishery Bulletin 101(4) 



deployed commercially to aggregate fish species at various 

 life history stages. FAD size is clearly relevant to those in- 

 terested in studying potential improvements to FAD design. 

 Carefully controlled studies on the importance of surface 

 area versus volume and the orientation of FAD structures 

 are needed. The role of a fouling community, too, deserves 

 further investigations. Although a fouling community may 

 weigh down streamers (trailing pieces of buoyant material 

 intended to increase the subsurface of area of a FAD), such 

 a community may also improve recruitment and possibly 

 retention of recruits around a FAD. Finally, the importance 

 of the initial recruits to a floating object should be studied 

 further. Enriching a FAD may increase the speed at which 

 additional fishes are recruited. Improved artificial fish may 

 prove more effective than the items used in the present re- 

 search. FADs are an important tool in a number of artisanal 

 (small-scale fishery based on traditional methods), sport, 

 and commercial fisheries, especially in tropical waters 

 where FAD fisheries particularly target tunas (Scomb- 

 ridae), jacks (Carangidae), and Coryphaena spp. (Galea, 

 1961; Klima and Wickham, 1971; Beets, 1989; Hilborn 

 and Medley 1989; Friedlander et al., 1994; Higashi, 1994; 

 Hall et al., 1999b). Due largely to the potential for fisheries 

 enhancement, considerable research has been focused on 

 the importance of floating-object characteristics and the 

 numbers of fishes attracted to such objects; however, the 

 results have been difficult to interpret and are often con- 

 flicting (Rountree, 1989; Kingsford, 1993; Druce and Kings- 

 ford, 1995). Because log sets in tuna purse-seine fisheries 

 (where fishermen target fish associated with drifting logs or 

 FADs) are associated with high levels of bycatch (Hall, 1998; 

 Lennert-Cody and Hall, 2000), the behavior and ecology of 

 flotsam-associated species is in urgent need of study so that 

 a means of reducing bycatch may be devised. 



This study made use of FADs floating at the surface; 

 studies by other researchers have employed similar tools 

 or they have used FADs tethered in mid-water. No one has 

 examined the effects of FAD position in relation to the sur- 

 face, and the implicit assumption appears to be that there is 

 no biologically significant difference. This assumption has 

 not been tested, although comparisons between data from 

 floating structures, whether at the surface, mid-water, or 

 tethered close to the bottom, are common in the literature. 

 I have made comparisons between my data from surface 

 FADs and results from mid-water FADs (e.g. Wickham and 

 Russell, 1974; Rountree, 1990); such comparisons may be 

 misleading and should be interpreted with caution. 



The results from the present study indicate that turn- 

 over rates at nearshore anchored FADs are high and that 

 undisturbed FAD assemblages may show little difference 

 in these rates from disturbed FADs. Fishes recruiting to 

 these FADs discriminate among potential floating objects, 

 forming larger, more species-rich assemblages around tri- 

 ple-size FADs than around single FADs. FADs possessing 

 a fouling biota also attract larger (though no more diverse) 

 assemblages than do clean FADs. The latter effect was 

 complicated by temporal fluctuations that overlay these 

 treatment effects, resulting in day-to-day changes in the 

 total numbers of fishes in both treatments (Table 4, Fig. 7). 

 Further, the presence of prior recruits in the enrichment 



experiment had a strong effect on subsequent recruitment. 

 Thus, the association of juvenile fishes with floating objects 

 is not a haphazard process, and floating-object character- 

 istics play potentially important roles in fish recruitment 

 to these objects. These results suggest that associating 

 with flotsam may be adaptive, rather than an accidental 

 behavior and support Kingsford's hypothesis (Kingsford, 

 1993 ) that floating material is an important environmental 

 component in the relationship between environment and 

 some juvenile fishes. 



Acknowledgments 



For help in the field, I am grateful to I. Nelson and D. 

 Mansue. W. L. Montgomery, S. Shuster, and to two anony- 

 mous reviewers who provided helpful criticism. Funding 

 was provided by the American Museum of Natural His- 

 tory (Lerner-Gray Fund), American Society of Ichthyolo- 

 gists and Herpetologists (Raney Award), Animal Behavior 

 Society, International Women's Fishing Association (Max 

 Coan Memorial Scholarship), Seaspace/Houston Underwa- 

 ter Club, Smithsonian Tropical Research Institute (STRI), 

 and Sigma Xi. D. R. Robertson of STRI and D. Margulise, 

 R. Olson, and V. Scholey of the Inter-American Tropical 

 Tuna Commission provided invaluable advice and logisti- 

 cal support. 



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