Hart et al.: Abundance, distribution, and activity patterns of demersal fishes on Hecate Bank, Oregon 
469 
Station 4 
Day I...,, 
" I "1 n 
R527 
Night M 
R528 
o'o 
0'5 
TO 
Station 9 
Day 
HI 
R537 
Night 
R538 
0.0 
0.5 
TO 
Station 2 
Day (HIT - 
— iuuth 
R531 
Niaht 
'I a 
0.0 
0.5 
1.0 
Station 3 
Day L .1 
rm 
R532 
Night fimm 
R533 
0.0 
0.5 
1.0 
Station 6 
Dav i 
-fe«.vl 
R534 
Night L 
11! 
Area (ha) 
Day 
Night 
11 Flat Rock 
B Flat Rock 
13 Rock ridge 
□ Rock ridge 
E] Boulder 
H Boulder 
□ Cobble 
H Cobble 
D Pebble 
02 Pebble 
□ Sand 
D Sand 
□ Mud 
□ Mud 
Figure 2 
Bar graphs indicate the area and relative 
composition (in hectares) of each primary 
habitat surveyed along transects during 
day and night periods for each station on 
Heceta Bank, OR. ROV dives associated 
with each station are identified by an “R” 
followed by the dive number. 
by rock ridge and boulder, mid-depth by cobble, and 
deeper areas by mud habitat with isolated patches of 
cobble and boulder. Rock ridge, boulder, cobble, and mud 
composed the four most dominant primary habitat types. 
Videotape analysis 
Videotape collected along all transects was analyzed for 
fish and habitat identification. Sunset, dawn, dusk, and 
nautical twilight times (Pacific daylight savings time) 
were derived from the U.S. Naval Observatory website 
(http://www.usno.navy.mil/, accessed June 2000) and 
calculated for the day of each dive by using the specific 
longitude and latitude coordinates (degrees and minutes) 
for each station. 
Transects were subdivided into habitat patches, based 
on primary habitat types observed on the videotapes. 
Seafloor habitats were classified into seven standard- 
ized categories (Hixon and Tissot 1 ; Stein et al., 1992): 
rock ridge (high relief where vertical rock was found 
to be >3.0 m); flat rock (low relief where vertical rock 
was found to be <3.0 m); boulder (300-25.6 cm rock); 
cobble (25.6-6.4 cm rock); pebble (6. 4-0. 2 cm rock); 
sand (2.0-0.06 mm); and mud (<0.06 mm). Only the pri- 
mary habitat (>50% of the seafloor) in the field of view 
was used in our analysis. The length of each habitat 
patch was determined by using the geographic position 
recorded at the start and end of each patch. With the 
scaling lasers, the width of each transect was estimated 
by selecting random frames every minute during each 
transect, measuring the width of these lasers on the 
video monitor, and extrapolating to the field of view. 
Transect width ranged from 1.3 to 2.1 meters. The 
area of each patch was determined by multiplying the 
patch length by the average patch width. Each transect 
consisted of a few to many habitat patches, depending 
on the variability of substrate. 
Videotape analysis was performed by two technicians 
simultaneously in order to confirm fish identifications, 
counts, and fish activity. All fishes were identified to 
the lowest practical taxonomic unit (usually to species) 
and total fish length was estimated to the nearest 5 
cm. For fish that could be identified to a taxonomic 
group, but not species, a generalized abbreviation was 
used (e.g., FF for unidentified flatfish), and in cases 
where the fish observed was one of two species, a new 
abbreviation was created to accommodate this situa- 
tion. Fish were counted at the point where they passed 
through the level of the scaling lasers and were as- 
signed a GMT time that became a permanent time and 
geographic reference point in a database. A single ana- 
tomical feature (eye) was used to determine whether or 
not a fish was considered within the transect to prevent 
underestimating transect width and overestimating 
abundance. We restricted our analysis to 31 identified 
species or taxonomic groups that were seen frequently 
enough to represent >0.1% of the total day and night 
fish density (number of fish per hectare). Exceptions to 
this rule were the inclusion of three rarely seen species: 
darkblotched rockfish (S. crameri), because this is an 
important commercial species; kelp greenling (Hexa- 
grammos decagrammus ); and bigfin eelpout ( Lycodes 
cortezianus), because the day-night activity patterns of 
the latter two have been studied in shallow temperate 
areas (Moulton, 1977). Some categories of multiple taxa 
were created, such as “pygmy-Puget Sound rockfish 
complex” {S. wilsoni and S. emphaeus), where it was 
impossible to identify every individual in aggregations. 
Another common category was “unidentified rockfish,” 
where it was not possible to classify a rockfish to spe- 
cies conclusively. “Unidentified juvenile rockfish” (ab- 
breviation RRF) were categorized by size (<10 cm long), 
not by morphological features, because video resolu- 
tion and inherent difficulty of in situ identification of 
young-of-the-year rockfishes precludes determinations 
at the level of species. Hagfishes (Eptatretus spp. ) were 
not identified to species, but on the basis of depth of 
