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Fishery Bulletin 95 ( I ), 1997 
clay-silt. This finding suggests that the distribution 
of juveniles within the preferred uniform sediment 
habitat is related more closely to water flow than to 
sediment pai tide size. Similar enhanced abundances 
of fish associated with anthropogenic sources have 
been proposed elsewhere (Mearns, 1974; Monaco et 
al., 1992) and in Hawaii (Henderson, 1992; Grigg, 
1994). 
In video deployments at many study sites, snap- 
pers were observed routinely picking at items in the 
lower water column and mouthing the substrate. 
DeMartini et al. (1996) determined that juvenile 
snappers at the north Kaneohe canyon eat a mix- 
ture of gelatinous drift, demersal crustaceans (am- 
phipods, etc.), and benthos (micromollusks, annelids, 
etc.). The majority of prey were <1 cm, of low motil- 
ity, and bottom associated. 
Habitats receiving drainage from shallower envi- 
ronments might have their food supply enhanced in 
at least two ways. First, fish may encounter and feed 
more frequently on suspended organisms and other 
materials flushed from shallower reef and estuarine 
environments (Gerber and Marshall, 1974). Second, 
the flow from shallow sources may elevate the or- 
ganics in sediments, thereby enhancing production 
of the benthos that snappers eat. Changes in benthic 
fauna at comparable depths (50-200 m) have been 
documented in relation to the flux of organics in the 
water column— both in natural (Buchanan and 
Moore, 1986) and anthropogenic situations (Nichols, 
1985). Benthos may also become enriched during 
large episodic movements of nutrient-rich bay sedi- 
ment to localized areas in the snapper grounds. The 
significant interaction, identified by the logistic 
model, of clay-silt with proximity to drainage sources 
supports the notion of enhanced organic input to the 
benthic community provided by such drainage. 
Distribution of juveniles in the archipelago 
Conventional fishing on the insular slopes of the ar- 
chipelago (332 km) identified few sites with juvenile 
snappers; the mode and median of the catch of juve- 
niles from all the gear was zero. Except for aggrega- 
tion sites at Oahu and Molokai, catches of juveniles 
occurred only in token numbers. In a 1967-68 dem- 
ersal trawl survey (n=6 2), Struhsaker sampled ~90 
km of relevant depths in the main Hawaiian Islands 
and similarly found the occurrence of juveniles to be 
infrequent and patchy. His catches of juvenile snap- 
pers had a mode of zero and median of one (Struh- 
saker, 1973). 
The 5 sites other than east Oahu that were sur- 
veyed by video (Table 6) each had substrate and 
depths consistent with those at east Oahu; 2 had 
sources of drainage; but only 1, south Molokai, sup- 
ported a snapper aggregation. South Molokai’s 
Kahanui swamp, located within the island’s exten- 
sive fringing reef complex, has a drainage channel 
similar in width and depth (15 m) to north Kaneohe 
Bay (U.S. Army Corps of Engineers, 1984). Its asso- 
ciated snapper aggregation is well situated to exploit 
the tidal drainage of the reef platform and swamp 
dispersed by westbound currents of the area 7 (Fig. 
6). The Hanalei estuary, on the island of Kauai, prob- 
ably fails to influence snapper depths because it dis- 
charges at a zone of high-energy mixing (~1 m depth) 
too far inshore from juvenile snapper grounds. 8 The 
site at Kahului, Maui, would have to have a very 
large coastal drainage feature to aggregate snappers; 
the distance between the snapper grounds and such 
a source would be twice that of the other sites sur- 
veyed. Presumably, any source of increased sus- 
pended materials (embayments, reef platforms, or 
atoll lagoons) could enhance snapper aggregations if 
depth, distance, and circulation characteristics fo- 
cused water and increased the frequency of sus- 
pended materials close to juvenile grounds (Cyrus 
and Blaber, 1983; Birkeland, 1984). 
Struhsaker, during his 1967-68 trawl survey, iden- 
tified one location (north coast of Oahu) with catches 
as high as 180 individuals in one haul. The substrate 
at the site was composed of uniform sediment and 
received discharge from two north Oahu rivers. How- 
ever, according to the surveys from the present work, 
the snapper depths at this site seem almost too far 
offshore (mean=4.5 km) to support an aggregation. 
Numerous attempts in 1990 (Table 5) to relocate this 
north Oahu aggregation with the same gear that was 
used in 1967-68 did not yield any snappers. Many 
changes that could have modified the suitability of 
this habitat for juveniles (e.g. heavy exploitation of 
the snapper stock [WPRFMC 2 ]; collapse of the coast’s 
large-scale irrigation-based agriculture and its drain- 
age; effects of increasing relief on juvenile grounds 
from the accumulation of incidental ocean dumping) 
have occurred in the 22 years between the surveys. 
Implications for the fish stock 
Regardless of what factors create premium habitat, 
the implications for the snapper stock of the archi- 
7 Wyrtki, K., V. Graefe, and W. M. Patzert. 1969. Current ob- 
servations in the Hawaiian Archipelago. Hawaii Institute of 
Geophysics HIG-69-15, 27 p. Hawaii Inst. Geophysics, 2525 
Correa Rd., Honolulu, HI 96822. 
8 U.S. Geological Survey. 1993. Water resources data Hawaii 
and other Pacific areas, water year 1993. Water-data Report 
HI-93-l:78-79. U.S. Geological Survey, 677 Ala Moana Suite, 
Honolulu, HI 96813. 
