FISHERY BULLETIN: VOL. 84, NO. 1 



8-1 



6- 



a, 5 _ 



4 - 



3 

 al 



2 - 



1 - 



~ I 1 1 1 I 



50 100 150 200 250 

 Abundance I f ish / ha I 



300 



Figure 7— The relationship between Townsend Cromwell CPUE 

 and Makalii abundance estimates. Line fitted by functional regres- 

 sion. See text for further discussion. 



(3.18 fish/line-h) to the average density of bottom fish 

 viewed from the submersible (118 bottom fish/ha). 

 The resulting estimate of q is 0.0269 ha/line-h. 



DISCUSSION 



The most enlightening aspect of this study was our 

 ability to perform an in situ assessment of factors 

 controlling the distribution and abundance of the 

 deep slope biota at Johnston Atoll. Organisms 

 showed not only distinct zonational patterns with 

 depth but clumped dispersion along horizontal 

 gradients as well. 



The fish fauna of Johnston Atoll is often con- 

 sidered a depauperate outlier of the Hawaiian fauna 

 (Gosline 1955; Randall et al. in press). In a later 

 paper, Gosline (1965) examined vertical zonation in 

 Hawaiian fishes, arguing that depth zonation pat- 

 terns are often sharply demarcated in intertidal and 

 shallow-water habitats, but these become increasing- 

 ly attenuated with depth. The results of our study 

 and Randall et al. (in press) support his conclusion 

 (see also Forster 1984). Some deep slope species have 

 extremely broad depth ranges (exceeding 200 m), yet 

 few representatives of the shallow-water communi- 

 ty extend appreciably beyond the 130 m escarpment 

 encircling the atoll. Other investigators have noted 

 that many Hawaiian species, which are commonly 

 thought of as strictly associated with coral reefs, 

 penetrate to depths well in excess of those favoring 

 the growth of scleractinian corals (Brock and Cham- 



berlain 1968; Strasburg et al. 1968; Clarke 1972). Yet 

 the distributions of these fishes are limited largely 

 to areas near the shelf break or shallower, while a 

 true deep slope ichthyofauna, comprised largely of 

 anthiids and lutjanids, exists along outer reef drop- 

 offs at both Johnston Atoll and in the Hawaiian 

 Islands. 



Distributional patterns of fishes were nonrandom 

 along horizontal gradients as well, as was readily ap- 

 parent in the atoll-wide distribution of Pristipo- 

 moides filamentosus . Based simply on catch totals, 

 60% more P. filamentosus were expected to occur 

 on the upcurrent exposure of the atoll than down- 

 current, although 760% more were observed there, 

 illustrating the clumped dispersion pattern which 

 characterized this species during fishing surveys. 

 Contagion was also evident in quadrat samples. 

 Future studies would be well advised to incorporate 

 statistical models consistent with these findings, in- 

 cluding use of the negative binomial distribution to 

 describe spatial patterns. 



On a more local scale, it was clear from submer- 

 sible observations that P. filamentosus and Etelis cor- 

 uscans were concentrated near underwater head- 

 lands. Brock and Chamberlain (1968) made similar 

 observations on deepwater populations of Chaetodon 

 miliaris, attributing the very localized distribution 

 of this species to increased accessibility of its food 

 (plankton) in the vertical turbulence plumes formed 

 by the impact of currents on underwater prom- 

 ontories. Because of its known planktivorous food 

 habits, this hypothesis could explain abundance pat- 

 terns of P. filamentosus. Moreover, fishermen empha- 

 size the importance of currents in locating feeding 

 aggregations of both P. filamentosus and E. cor- 

 uscans. These two species taken together comprise 

 the most important species landed in the Hawaiian 

 deep-sea hook-and-line fishery, both in terms of yield 

 and economic value. The relative abundance of these 

 species in the deepwater bottom fish community may 

 be due to their utilization of an allochthonous plank- 

 ton resource transported to neritic waters from the 

 open sea. 



Bottom Fish Abundance 



Certain methodological problems hindered this 

 study and should be reviewed before comparing the 

 abundance estimates from the two surveys. Any 

 technique, including those used here, has its own spe- 

 cific combination of advantages and disadvantages. 



There is ample reason to suspect bias in assess- 

 ments based on underwater visual surveys. Sale and 

 Douglas (1981) have shown that a single visual fish 



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