474 
Fishery Bulletin 108(4) 
Table 2 
Fish taxa (raw count s) exhibiting a significant difference in the percentage of fish found to be active and inactive during day and 
night within similar primary habitat types (rock ridge, boulder, cobble, and mud) over all stations at Heceta Bank, OR. Values 
represent the percentage of fish found to be active or inactive over each substrate type, and values in parentheses indicate n for 
each comparison. Wilcoxon signed-rank test was used (*P<0.05, **P<0.01, not significant [ns], P>0.05). Taxa are listed in order 
of highest abundance (number of fish per hectare) within each category. 
Taxon 
Primary 
habitat 
Day 
active fish 
Day 
inactive fish 
Night 
active fish 
Night 
inactive fish 
Diurnal 
rosethorn rockfish (S. helvomaculatus) 
rock ridge 
76% (246)** 
ns 
boulder 
74% (243)** 
85% (123)** 
cobble 
66% (405)* 
92% (143)** 
mud 
ns 
93% (47)** 
Nocturnal 
Eptatretus spp. 
cobble 
87% (23)* 
69% (29)* 
Significantly more active during day 
unidentified juvenile rockfish 
rock ridge 
99% (855)** 
( Sebastes spp.) 
boulder 
98% (1214)** 
cobble 
96% (876)** 
mud 
91% (54)** 
Puget Sound rockfish (S. emphaeus) 
boulder 
71% (367)** 
cobble 
73% (2501)** 
mud 
87% (126)** 
pygmy rockfish (S. wilsotii) 
rock ridge 
99% (855)** 
cobble 
99% (235)** 
mud 
94% (34)** 
yellowtail rockfish (S. flavidus) 
rock ridge 
95% (259)** 
boulder 
96% (260)** 
Significantly more active during night 
spotted ratfish (Hydrolagus colliei ) 
boulder 
87% (16)* 
mud 
92% (87)* 
widow rockfish (S. entomelas) 
boulder 
96% (45)* 
and hagfishes exhibited distinct diurnal and nocturnal 
activity, respectively. These day and night patterns were 
similar to those observed during day-time surveys from 
manned submersibles on Heceta bank (Pearcy et al., 
1989; Stein et al., 1992; Hixon et al. 2 ), day and night 
surveys on Stonewall Bank (Hixon and Tissot 1 ), and are 
generally consistent with most patterns found in other 
shallow temperate day and night studies, but were much 
less distinct than those for fishes inhabiting tropical 
fish communities (Helfman, 1978). The overall marked 
decrease in abundance and activity of smaller-size taxa 
at night was similar to the decrease that Ebeling and 
Bray (1976) and Moulton (1977) observed, but our study 
did not provide evidence of a pronounced replacement 
of diurnally active taxa by exclusively nocturnal spe- 
cies as observed at Santa Catalina Island (Hobson and 
Chess, 1973; Hobson et al., 1981), Hawaiian tropical 
reefs (Hobson, 1972), and reefs in the Virgin Islands 
(Colette and Talbot, 1972). 
It is possible that light illumination at the top of 
Heceta Bank during the day contributed to the higher 
abundance and activity of the three most dominant 
day taxa (pygmy rockfish, pygmy-Puget Sound rockfish 
complex, and unidentified juvenile rockfish), as found in 
similar studies on temperate species. Fishes found at 
the top of Heceta Bank likely perceive and use the faint 
sun illumination during the day (Boehlert, 1979). On 
Heceta Bank, the photic zone generally extends down 
to approximately 50 m water depth and it is generally 
accepted that sun illumination affects behavior of fishes 
down to these depths (L. Britt, personal commun. 4 ). 
This was confirmed by the GLOBEC survey, which mea- 
sured one percent of surface light at 50 m, just above 
the shallowest fish survey depths (70 m) where most of 
the unidentified juvenile rockfish were present. Light il- 
lumination may be aiding the dominant day assemblage 
because these taxa stay close (perhaps within visual 
distance) to large features that provide refuge from 
larger, active piscivorous predators. In Puget Sound 
4 Britt, Lyle L. 2007. Alaska Fisheries Science Center, 
National Marine Fisheries Service, National Oceanic and 
Atmospheric Administration, 7600 Sand Point Way N.E., 
Seattle, WA 98115. 
