Reum and Essington: Season- and depth-dependent variability of a demersal fish assemblage in a fjord estuary 
191 
□October H March H July 
Figure 3 
Average species richness (N\ upper panel) for (A) October and July 
samples and (B) October, March, and July (all-months) by depth sampled. 
Average species diversity (H'\ lower panel) for October and July samples 
(C) and October, March and July ( D ) . Lower case letters above each 
depth category denote depths that do not differ on the basis of post 
hoc Tukey honestly significant difference tests. (A) and (C) correspond 
to October+July two-way ANOVA tests and (B) and (D) correspond to 
all-months two-way ANOVA tests. H' differed by month only for the 
October+July. Note: depths at 20 and 80 m were not sampled in March. 
Error bars indicate standard deviation. For October, March, and July, 
4, 4, and 5 sites were sampled at each depth, respectively. 
notatus ; Fig. 4). In shallow waters (20 
and 40 m) several flatfishes dominated 
including small and large English sole, 
rock sole ( Lepidopsetta bilineata), C-0 
sole ( Pleuronichthys coenosus ), Pacific 
sanddab ( Citharichthys sordidus ), and 
sand sole iPsettichthys melanostictus) 
among other species (Fig. 4). 
In the October+July analyses, tem- 
poral changes in assemblage structure 
were largely driven by species that were 
found primarily at depths of 80 m. The 
biomass of shiner perch, pile perch, 
walleye pollock, and Pacific tomcod was 
highest in October and the biomass of 
large spiny dogfish and slender sole was 
highest in July (Fig. 4). At depths of 20 
and 40 m, the biomass of small English 
sole and C-0 sole was highest in Octo- 
ber and the biomass of staghorn sculpin 
(Leptocottus armatus ) and sand sole was 
highest in July. The biomass of species 
that typified the 160-m depths changed 
little between October and July (e.g., 
spotted ratfish, dover sole, rex sole, and 
Pacific hake; Fig. 4). In the all-months 
analysis, species with higher biomass 
in March included C-0 sole, sand sole, 
great sculpin, and rock sole (Fig. 4). 
Size-based analysis 
Body sizes encountered in the survey 
spanned eleven size classes, ranging 
from 2 to 2048 g. Overall, biomass spec- 
tra were nonlinear in appearance and 
approximately parabolic for most depth 
and season combinations (Fig. 5). For 
that reason metrics describing linear biomass size spec- 
tra (intercept, slope) were not estimated. Deep waters 
were dominated by individuals larger than 32 g, whereas 
shallow waters contained relatively more individuals 
that were less than 128 g (Fig. 5). Temporal differences 
were most apparent at depths of 80 m where biomass 
was concentrated in body size classes greater than 128 g 
in July and at 40 m that contained peak biomass levels 
in the 16-g body size class in March. Overall, 28% and 
29% of the biomass spectra variance was associated 
with depth in both all-months (F^ 10] = 5.4, P<0.001) and 
October+July tests (F (3 10) = 2.3, PcO.001), respectively. 
Month explained a smaller but significant proportion 
of variance in the October+July test (11%; F, x 10 ,=2.1, 
PcO.001) and was not a significant predictor in the all 
seasons test (P| 133! =2.1, P=0.09). Variance explained 
jointly by season and depth was again zero. 
In the October+July analyses, the first CCA axis ac- 
counted for 20.9% of the total variation and separated 
the shallow (20 and 40 m) and deep assemblages (160 
m). The second axis accounted for 10.3% of the variance 
and distinguished 80 m from the other depths. The 
largest size class (2048 g) was associated with depths 
of 80 m, and the next three largest size classes (256, 
512, and 1024 g) were associated with depths of 160 m 
(Fig. 6). In contrast, the smallest size classes (4, 8, and 
16 g) were affiliated with depths of 20 and 40 m. The 
remaining intermediate body size classes were near the 
origin of the ordination plot and not closely associated 
with any of the depths. The analysis of all-months tests 
reiterated these patterns (Fig. 6). Tracking the arrival 
of dogfish, the size classes with the strongest temporal 
responses were also the largest size classes (1024 and 
2048 g) which exhibited higher abundances in July (Fig. 
6). In October, biomass in the smallest size classes (2, 
8, and 16 g) was relatively higher. 
Discussion 
Fjord systems such as Puget Sound typically possess 
steep bathymetries and deep basins that result in deep- 
water habitat relatively close to shore. As expected, 
the demersal fish assemblage in Puget Sound varied 
