Barber et al.: Demersal fish assemblages of the northeastern Chukchi Sea 
207 
was different for each species assemblage. Their spe- 
cies assemblages and sediment types, however, did 
not coincide exactly; two sediment types were found 
in the same depth range of species assemblages. They 
suggested that faunal similarities were maintained 
in regions of sediment transition and that factors 
other than sediment type governed distribution of 
assemblages. Similarly, Pearcy (1978) found a clear 
separation in the effects of depth but not in the ef- 
fects of sediment for two assemblages, one shallow 
and one deep. There was, however, an interaction 
between depth and sediment type where the shal- 
low assemblages showed a high similarity between 
stations of different sediment types. 
In respect to the hydrography of this area, the ACC 
sweeps through the area in a general northwest flow. 
However, change in wind conditions may cause peri- 
odic and persistent reversals in the southerly flow of 
the ACC (Johnson, 1989; Weingartner 4 ). Flow rever- 
sals tend to be more common during winter ice cover. 
A review of long-term ice records suggests that in 
summer, an oceanographic front (as represented by 
the southern ice edge) may exist to the south and 
east of Point Franklin. However, there is much 
interannual variation in the location of this front, in 
related flow patterns, and in potential transport of 
adult and larval fishes into the area from the south. 
Variations in hydrographic conditions, coupled 
with differences in catches and changes in year-class 
strength, strongly suggest that there are interannual 
changes in abundance and distribution of fishes 
within the study area. How, or if, the dynamics of 
oceanographic parameters are translated into dis- 
tributions and relative abundances of fishes and fish 
assemblages is unknown. Differences in catches at 
stations sampled in 1990 and 1991 may have been 
due to interannual changes in fish distribution and 
abundance, or even to sampling error. However, dif- 
ferences in the age-class structure of fishes captured 
during the two years are striking. In 1990 approxi- 
mately 42% of G. tricuspis (Smith et al., 1996b) were 
older than 4 years, but in 1991 only 9% were older than 
4 years. Similarly, ages of H. robustus in 1990 ranged 
from 1 to 11, and age class 5 was most abundant (Smith 
et al., 1996a), whereas ages reported by Pruter and 
Alverson ( 1962) for this species were 6 to 13, and ages 
7 through 9 accounted for 90% of the fish samples. 
Interannual change in the distribution and rela- 
tive abundance of fish species may not lead to differ- 
ent associations or result in a change in the loca- 
tions of these fish within the study area. Overholtz 
4 Weingartner, T. J. 1994. Institute of Marine Sciences, Univ. 
Alaska Fairbanks, Fairbanks, AK 99775-7220. Personal 
commun. 
and Tyler (1985) concluded that, even though some 
assemblages changed dramatically in species rich- 
ness and relative abundance, the spatial integrity of 
each complex remained constant over time. Similarly, 
there were seasonal changes in species associations 
on the Scotian Shelf, but these were relatively con- 
stant over 9 years within seasons (Mahon and Smith, 
1989). Colvocoresses and Musick (1984) examined 9 
years of trawl data from the Middle Atlantic Bight, 
and the distributional patterns that were found were 
largely structured by temperature on the innershelf 
and midshelf and by depth on the outer shelf and 
shelf break. They also found that there was sedimen- 
tary and topographical uniformity for both the 
innershelf and midshelf and that there were no 
strong relationships between species group and sedi- 
ment. Like Mahon and Smith (1989), Colvocoresses 
and Musick (1984) found good geographic definition 
in both autumn and spring groups and overlap be- 
tween groups. The groups that made up the commu- 
nities had much in common but differed between 
seasons. Colvocoresses and Musick ( 1984) also found 
relationships between groups and depth, and shifts 
in the groups with changes in temperature. For ex- 
ample, the geographic extent of assemblages varied 
between years depending on the southward extent 
of the cooler 8°C water. The fish apparently behave 
as a group in response to environmental variation. 
The fish assemblages in our study were depicted 
as having clear assemblage boundaries related to 
sediment type and oceanographic features. Results 
from a principal coordinate analysis, however, indi- 
cate that these boundaries are related to other fea- 
tures as well. Therefore, the assemblages shown in 
the ordination plots should more appropriately be 
thought of as transitional species abundances and 
proportional compositions. This conclusion is simi- 
lar to that reached by McKelvie ( 1985), namely that 
assemblages of mesopelagic fishes were best inter- 
preted as gradations between faunas associated with 
different water masses. Consequently, our study area 
may be viewed as a transition zone between fish com- 
munities of the southern Chukchi Sea and those of 
the Arctic Ocean. In this view, the presence of differ- 
ent species assemblages in the northeastern Chukchi 
Sea represents a mixture of 2 fish communities whose 
abundance and biomass vary, shifting somewhat off- 
shore-onshore or northerly-southerly, according to 
variations in the oceanographic structure of the area. 
Acknowledgments 
We would like to thank T. Sample, C. Armistead, and 
T. Dark, National Marine Fisheries Service, as well 
