RALSTON ET AL.: BOTTOM FISH RESOURCE AT JOHNSTON ATOLL 



census seldom records all individuals present at the 

 time of the census. Similarly, Colton and Alevizon 

 (1981) showed that a quarter of the community they 

 studied was characterized by significant diurnal 

 changes in abundance. They concluded that unless 

 sampling time is carefully controlled and standard- 

 ized, results from visual abundance surveys may be 

 seriously biased. Standardization was achieved in this 

 study because all 10 dives started between 0840 and 

 0950 in the morning and each lasted 4 h. Further- 

 more, Brock (1982) showed that large, conspicuous, 

 diurnally active species are accurately censused with 

 visual assessment techniques, although the most 

 abundant are often underestimated. With the excep- 

 tion of Cookeolus boops, which, although nocturnal, 

 shelters in the open along the slope face, all of the 

 species included in the quadrat sampling fit these 

 criteria. Biases which frequently accompany visual 

 assessments have thus been considered and mini- 

 mized here 



Another factor which may have affected the results 

 of Makalii surveys is attraction and repulsion of cer- 

 tain species to and from the submersible Previous 

 investigators have typically ignored this problem (Uz- 

 mann et al. 1977; High 1980; Powles and Barans 

 1980; Carlson and Straty 1981), while at the same 

 time acknowledging that some species are attracted 

 (ag, black sea bass, southern porgy Pacific halibut, 

 sculpin, and yelloweye rockfish) or repelled (eg, 

 squid, herring, mackerel, butterfish, and wolf eel) to 

 submersibles and divers. Nevertheless, as pointed out 

 by Uzmann et al. (1977), one can at least observe the 

 reactions of species to the submersible's presence, 

 giving the viewer the opportunity to evaluate poten- 

 tial sources of error. We have attempted to address 

 this problem by pooling counts for all species. While 

 admittedly this procedure may not remove all bias, 

 it is our feeling that in the absence of more quan- 

 titative information, little else can be done to im- 

 prove the data. Studies are now being implemented 

 to specifically evaluate the degree of attraction or 

 repulsion of different species to the Makalii. 



Provided an awareness of these concerns, the 

 results presented here support the contention that 

 the catch of bottom fish/line-h is a suitable CPUE 

 statistic This conclusion is based on the data pre- 

 sented in Figure 7, where CPUE generally increases 

 with fish density and the regression intercept passes 

 close to the origin. Although the relationship is 

 statistically insignificant, this is likely due to small 

 sample size (n = 6). Moreover, differences in bottom 

 fish abundance between upcurrent and downcurrent 

 locations were shown to result largely from the con- 

 tagious dispersion of Pristipomoides filamentosus 



along the eastern side of the atoll, where its primary 

 food resource first becomes available for consump- 

 tion. 



The estimation of catchability for deep-sea hook- 

 and-line gear is a useful application of the dual sam- 

 pling program presented hera The results suggest 

 relatively great sensitivity of bottom fish stocks to 

 exploitation pressure, a finding consistent with pre- 

 vious and ongoing studies (Ralston 1984). If we use 

 q = 0.0215 ha/line-h as an estimate of catchability, 

 we conclude that 1 line-h of Townsend Cromwell fish- 

 ing effort removes about 2.2% of the bottom fish 

 inhabiting 1 ha of habitat. A similar finding was 

 reported by Polovina 9 , who estimated q from the 

 same vessel for a Mariana stock of bottom fish. Re- 

 movals such as this are not insubstantial and under- 

 score the importance of developing methods of stock 

 assessment which can be used early in the develop- 

 ment of a fishery and in the absence of conventional 

 data sources. A combination of surface platform 

 surveys with submersible ground-truthing is certain- 

 ly a promising assessment technique to pursue (Uz- 

 mann et al. 1977). 



ACKNOWLEDGMENTS 



We would like to thank the U.S. Army Corps of 

 Engineers Pacific Ocean Division, the U.S. Army 

 Toxic and Hazardous Materials Agency, and the Na- 

 tional Undersea Research Program at the Univer- 

 sity of Hawaii for making this study possible Special 

 thanks go to the staff of the Hawaii Undersea Re- 

 search Laboratory Program and the Makalii opera- 

 tions crew for help in coordinating the dive program 

 and in meeting our needs for logistical support. 



LITERATURE CITED 



Amerson, A. B., Jr., and P. C. Shelton. 



1976. The natural history of Johnston Atoll, central Pacific 

 Ocean. Atoll Res. Bull. 192:1-479. 

 Bannerot, S. P., and C. B. Austin. 



1983. Using frequency distributions of catch per unit effort 

 to measure fish-stock abundance Trans. Am. Fish. Soc. 

 112:608-617. 

 Barans, C. A., and D. V. Holliday. 



1983. A practical technique for assessing some snapper/group- 

 er stocks. Bull. Mar. Sci. 33:176-181. 

 Barkley, R. A. 



1972. Johnston Atoll's wake J. Mar. Res. 30:201-216. 

 Bray, R. N. 



1981. Influence of water currents and zooplankton densities 



9 Polovina, J. J. A variable catchability version of the Leslie 

 model with application to an intensive fishing experiment on a 

 multispecies stock. Manuscr. submitted to U.S. Natl. Mar. Fish. 

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