Hart et al.: Abundance, distribution, and activity patterns of demersal fishes on Hecate Bank, Oregon 
467 
those observed in warmer water regions (Hobson et 
al., 1981). Deepwater habitats with low light penetra- 
tion would therefore be expected to show only subtle 
changes in species composition, densities, or activities 
during night hours. Nevertheless, diel distributions 
and activity patterns of some species of fish have been 
observed in temperate areas at substantial depths. On 
Stonewall Bank, Oregon, in situ direct observations in 
shelf waters (41-70 m) revealed that species composition 
changed little from day to night, but the abundance of 
some fishes decreased dramatically (Hixon and Tissot 1 ). 
Specifically, juvenile rockfishes ( Sebastes spp. ) and ro- 
sethorn rockfishes (S. helvomaculatus) showed much 
greater abundance during the day, and spotted ratfish 
( Hydrolagus colliei ) and widow rockfish (S. entome- 
las ) were significantly more abundant at night. Within 
Pribilof Canyon (181 to 240 m) in the Bering Sea, Pa- 
cific ocean perch ( S . alutus) actively fed on euphausiids 
just above sea-whip “forests” during the day and were 
observed to be less active within the sea-whip habitat at 
night (Brodeur, 2001). In deeper rocky bank areas with 
lower levels of ambient light, it is not known whether 
an overall change from high to low activity from day 
to night exists, as is observed in shallow temperate 
fish communities (Ebeling and Bray, 1976; Hobson and 
Chess, 1976; Moulton, 1977). 
We hypothesized there would be differences in the 
day and night assemblages of fishes in deep temperate 
waters, but that the patterns and changes in abundance 
and activity would be less distinct than those observed 
in tropical and shallow temperate fish communities. 
Given its diverse range of habitats and water depths, 
Heceta Bank is an ideal location for studying day-night 
patterns of demersal fishes among different depths and 
habitat types. 
Materials and methods 
Study area 
Heceta Bank is one of the largest of all submarine, 
rocky banks off the west coast of the United States, 
located approximately 60 km off the central Oregon 
coast, extending 50 km north to south (Fig. 1). The bank 
has been a primary focus of direct-observation studies of 
groundfishes, invertebrates, and habitat since the late 
1980s (Pearcy et al., 1989; Stein et al., 1992; Wakefield 
et al., 2005; Whitmire et al., 2007; Hixon and Tissot 1 ; 
Hixon et al. 2 ). This bank comprises a wide range of 
1 Hixon, M. A., and B. N. Tissot. 1992. Fish assemblages of 
rocky banks of the Pacific Northwest. Final Report supple- 
ment, OCS Study 91-0025, 128 p. U.S. Minerals Manage- 
ment Service, Camarillo, CA 93010. 
2 Hixon, M. A., B. N. Tissot, and W. G. Pearcy. 1991. Fish 
assemblages of rocky banks of the Pacific northwest, Heceta, 
Coquille, and Daisy Banks. OCS Study MMS 91-0052, 410 p. 
U.S.D.I. Minerals Management Service, 770 Paseo Camarillo, 
2 nd Floor, Camarillo, CA 93010. 
benthic habitats from rock ridge and boulder to sand, 
and mud and extends from 70 m depth at the top of the 
bank to >500 m in water depth on its flanks (Figs. 1 and 
2). The bank has been generally characterized as having 
three major habitat-depth profiles: 1) shallow rock ridge 
and boulder habitat from 70 to 100 m; 2) boulder and 
cobble habitat at mid-depth from 100 to 150 m; and 3) 
mud habitat in greater than 150 m of water depth (Hixon 
et al. 2 ). Some portions of the bank show great habitat 
variability (Hixon and Tissot 1 ). 
Light levels 
Ambient light levels on Heceta Bank were measured 
two weeks before the current study by the Plankton/ 
Bio-Optics group at Oregon State University during a 
Global Ocean Ecosystems Dynamics (GLOBEC) study of 
meso- and fine-scale physical and biological fields (Whit- 
mire and Cowles, unpubl. data 3 ). In order to characterize 
the underwater light environment over the bank, the 
OSU group used in situ total absorption coefficient data. 
Absorption measurements (a t [488 nm|) were collected 
with a dual-path absorption and attenuation meter (ac-9; 
WET Labs, Inc., Philomath, OR) that was mounted on 
a SeaSOAR, a towed undulating vehicle used to deploy 
a wide range of oceanographic monitoring equipment, 
and towed in an undulating fashion along east to west 
track lines over the bank during daylight hours on 5 
and 6 June 2000. One percent light levels (in relation 
to surface light values), a commonly used oceanographic 
parameter for comparing light attenuation, were reached 
at approximately 20 m in high chlorophyll coastal waters 
(~3 to 6 mg/m), and at approximately 50 m in waters 
at the western end of the east— west transects. This 
empirical approach for light attenuation agreed well 
with theoretical relationships between depth and light 
attenuation as applied to coastal and offshore waters 
within the California Current (Morel, 1988; Barnard 
et al., 1999). 
Survey transects 
From 19 to 26 June 2000, an interdisciplinary group 
of scientists used the remotely operated vehicle (ROV) 
ROPOS (Remote Operated Platform for Ocean Science), 
managed and operated by the Canadian Scientific Sub- 
mersible Facility (CSSF), to revisit five stations on 
Heceta Bank that were established in the 1980s (Figs. 
1 and 2) (Pearcy et al., 1989; Stein et al., 1992; Hixon 
and Tissot 1 ; Hixon et al. 2 ) and to explore new sites on the 
bank. At each of five historical stations fish assemblages 
were compared between day and night. 
The ROV ROPOS is well suited for deepwater demer- 
sal fish surveys. ROPOS is a 30-horsepower electro- 
hydraulic ROV equipped with two video systems, a 
3 Whitmire, A. L., and T. J. Cowles. 2008. College of Oceanic 
and Atmospheric Sciences, Oregon State Univ., Corvallis, 
OR 97331. 
