186 
Season- and depth-dependent variability 
of a demersal fish assemblage 
in a large fjord estuary 
(Puget Sound, Washington) 
Jonathan C. P. Reum (contact author) 
Timothy E. Essington 
Email address for contact author: reumj@u.washington.edu 
School of Aquatic and Fishery Sciences 
Box 355020 
University of Washington 
Seattle, Washington 98195 
Abstract — Fjord estuaries are com- 
mon along the northeast Pacific coast- 
line, but little information is available 
on fish assemblage structure and its 
spatiotemporal variability. Here, we 
examined changes in diversity met- 
rics, species biomasses, and biomass 
spectra (the distribution of biomass 
across body size classes) over three 
seasons (fall, winter, summer) and at 
multiple depths (20 to 160 m) in Puget 
Sound, Washington, a deep and highly 
urbanized fjord estuary on the U.S. 
west coast. Our results indicate that 
this fish assemblage is dominated by 
cartilaginous species (spotted ratfish 
I Hydrolagus colliei] and spiny dog- 
fish [Squalus acanthias ]) and there- 
fore differs fundamentally from fish 
assemblages found in shallower estu- 
aries in the northeast Pacific. Diver- 
sity was greatest in shallow waters 
(<40 m), where the assemblage was 
composed primarily of flatfishes and 
sculpins, and lowest in deep waters 
(>80 m) that are more common in 
Puget Sound and that are dominated 
by spotted ratfish and seasonally 
(fall and summer) by spiny dogfish. 
Strong depth-dependent variation in 
the demersal fish assemblage may be 
a general feature of deep fjord estuar- 
ies and indicates pronounced spatial 
variability in the food web. Future 
comparisons with less impacted fjords 
may offer insight into whether carti- 
laginous species naturally dominate 
these systems or only do so under 
conditions related to human-caused 
ecosystem degradation. Information 
on species distributions is critical 
for marine spatial planning and for 
modeling energy flows in coastal food 
webs. The data presented here will aid 
these endeavors and highlight areas 
for future research in this important 
yet understudied system. 
Manuscript submitted 6 July 2010. 
Manuscript accepted 3 February 2011. 
Fish. Bull. 109:186-197 (2011). 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Estuaries are highly productive habi- 
tats that support a diversity of spe- 
cies, but have suffered because of 
growing human demands (Kennish, 
2002; Lotze et al., 2006). Recognition 
of declining fish, marine mammal, 
and seabird populations and the need 
to consider the multiplicity of caus- 
ative agents for these declines and 
their ecological consequences have 
prompted an interest in adopting eco- 
system-based approaches for manage- 
ment, whereby knowledge of ecological 
interactions, such as trophodynamic 
control and competition is used to 
inform policy decisions (Pikitch et al., 
2004). Our ability to implement more 
holistic management approaches, how- 
ever, can be limited by a lack of basic 
information on the distribution and 
abundance of species that a system 
comprises and how these vary over 
time and space. This information is 
particularly lacking for fjord estuar- 
ies that are common features along 
the northeast Pacific coastline. Fjord 
estuaries differ from other estuar- 
ies by possessing a deep inner basin 
that is separated from continental 
shelf waters by a shallow sill near 
the mouth of the estuary. Although 
some of these ecosystems are remote 
and show little sign of degradation, 
commercial and recreational fishing, 
aquaculture, shoreline development, 
pollution, and logging are degrading 
a growing number of them. 
Puget Sound, WA, is the south- 
ernmost fjord estuary in the north- 
east Pacific and supports major ur- 
ban centers with a combined human 
population of 4 million (PSAT 1 ). Over 
the past 150 years Puget Sound has 
been commercially fished and sub- 
ject to increasing rates of habitat 
loss, eutrophication, pollution, and, 
more recently, acidification. Presently, 
commercial fishing for groundfish is 
not permitted, but some species (e.g., 
Sebastes spp., lingcod [Ophiodon elon- 
gates ]) are targeted by recreational 
fishermen. Although an ecosystem- 
based approach is clearly relevant 
for Puget Sound, there is a paucity 
of published information on how the 
demersal fishes of Puget Sound use 
different habitats, and thus a need 
for studies on assemblage structure. 
Identifying major patterns of as- 
semblage variability along different 
habitat gradients has practical impli- 
cations not only for modeling energy 
flows, but for devising monitoring 
schemes that can adequately quantify 
interannual changes in population 
abundance (Greenstreet et al., 1997; 
Thompson and Mapstone, 2002). Al- 
though project and agency reports 
provide some descriptive analyses on 
Puget Sound fish communities, peer- 
reviewed literature on demersal fish 
distributions from other deep fjords 
in the northeastern Pacific are rare. 
1 PSAT (Puget Sound Action Team). 2007. 
State of the Sound. 2007. Publication 
no. PSAT 07-01, 96 p. Office of the Gov- 
ernor, Olympia, State of Washington. 
[Available at: http://www.psp.wa.gov/ 
documents.php, accessed February 2011.) 
