numerous pelagic and demersal fish species. Origi- 

 nally thought to be of little nutritional value, these 

 tunicates have been found to contain filtered con- 

 centrations of phytoplankton and microzooplankton, 

 thereby elevating the preys' food value. Regional 

 and highly localized oceanographic processes will 

 affect the distribution of such potential planktonic 

 prey, and exploitation of these resources may influ- 

 ence the local distribution of predator species (Brock 

 and Chamberlain 1968; Bray 1981). Deepwater 

 snappers are most abundant on slopes of upcurrent 

 exposure and near underwater headlands at John- 

 ston Atoll (Ralston et al. 1986). These abundance 

 patterns were attributed to planktonic concentra- 

 tions created by mesoscale oceanographic processes 

 as noted with other fishes on bank or slope habi- 

 tats (Isaacs and Schwartzlose 1965; Pereyra et al. 

 1969). 



Polovina (1986) suggested that fishing may selec- 

 tively deplete one species, such as P. zonatus, 

 preferentially over another (P. auricilla) and there- 

 by alter the species composition in a given locality. 

 With the small degree of dietary overlap between 

 the two species in this study, such selective removal 

 of P. zonatus will decrease predation pressure on 

 the demersal prey resources of this species and, as 

 evidenced in Larson (1980), may ultimately allow 

 greater niche breadth for coexisting predator 

 species. 



In conclusion, this study has provided qualitative 

 insight into dietary habits of two sympatric, deep- 

 water species and has permitted some inferences 

 regarding their ecology. Much more study is needed 

 to comprehend fully the role of these predators in 

 the ecosystem. Logistical constraints, including the 

 problem of regurgitation, will continue to make 

 quantitative assessments of diet a difficult task un- 

 til new capture methodologies are developed. How- 

 ever, the rewards in improved understanding of 

 deepwater ecology and increased ability to manage 

 these valuable stocks suggest that the efforts will 

 be justified. 



Acknowledgments 



We thank G. W. Boehlert, R. E. Bowman, C. B. 

 Grimes, J. D. Parrish, J. J. Polovina, S. Ralston, and 

 the two anonymous reviewers for their helpful com- 

 ments on various drafts of the manuscript. This 

 paper is a result of the Resource Assessment Inves- 

 tigation of the Mariana Archipelago at the South- 

 west Fisheries Center Honolulu Laboratory, Nation- 

 al Marine Fisheries Service, NOAA. 



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