Laidig et al.: Reactions of fishes to a manned submersible and a remotely operated vehicle 
59 
of the type of lighting and camera (see Materials and 
methods section). 
We used 26 taxa of fishes in the analyses of fish 
reactions to the submersible and ROV (Table 1). Half- 
banded ( Sebastes semicinctus; 25%), Blue (S. mystinus; 
24%), and Pygmy (S. wilsonr, 12%) Rockfishes were 
the most abundant species observed from the Delta 
submersible, and Halfbanded (56%) and Pygmy (22%) 
Rockfishes were most abundant in the ROV survey. In 
total, observations of 1161 fishes for the Delta sub- 
mersible and 9206 fishes for the ROV were used in the 
analyses of directional movements and distance of re- 
action from each vehicle. 
Fewer fishes reacted to the manned submersible 
(11% of all fishes; Table 1) than to the ROV (57% of all 
fishes). The minimum distance of a fish reaction was 
0.5 m from the submersible (96% of reactions were at 
a distance >1 m) and 1 m from the ROV. The percent 
reaction varied from 0% for several species to 54% for 
the Squarespot Rockfish (S. hopkinsi) observed from 
the submersible and from 0% for some species to 84% 
for Pink Seaperch, (Z alembius rosaceus) for fishes ob- 
served from the ROV. Of those taxa observed from the 
submersible, only Squarespot Rockfish had a reaction 
rate of at least 50%. Six taxa observed with the ROV 
had a reaction rate of at least 50%: Pink Seaperch, 
Pacific Hake ( Merluccius productus), Spotted Ratfish 
(Hydrolagus colliei), and Yellowtail (S. flauidus), Ca- 
nary (S. pinniger), and Halfbanded Rockfishes. Cow- 
cod, Bocaccio (S. paucispinis), and Canary Rockfish are 
of particular concern to fishery managers and in need 
of improved assessments (Hilborn et al., 2011; PFMC, 
2011). The reaction rate of these 3 species to the sub- 
mersible ranged from 8% to 19%; their reactions to the 
ROV varied from 20% to 56%. Thornyheads, YOY rock- 
fishes, and hagfishes had reaction rates <10% to either 
vehicle. Fishes of 5 taxa did not react at all to the sub- 
mersible, and 1 group of taxa (YOY rockfishes) that did 
not react to the ROV. 
Fish reactions to both vehicles increased significant- 
ly as fish distance above the seafloor increased, and 
this trend in reaction was greater for the ROV than for 
the submersible (all fishes combined, P<0.001; Table 2; 
Fig. 3). Only 2% of the fishes observed on the seafloor 
during submersible surveys (i.e., 27 of 1261 fishes) and 
7% observed near the seafloor (i.e., 410 of 6009) reacted 
to this vehicle. However, 18% of fishes on the seafloor 
(i.e., 512 of 2895) reacted to the ROV, with Halfbanded 
Rockfish and Blackeye Goby ( Rhinogobiops nicholsii ) 
accounting for 71% of these reactions (361 out of 512 
fishes that reacted; Table 2). During the ROV surveys, 
fishes near the seafloor reacted more than fishes in 
contact with the seafloor (59% versus 18%, respective- 
ly), with Halfbanded and Pygmy Rockfishes represent- 
ing 93% of these reactions (3800 out of 4083 fishes that 
reacted). Fishes in the midwater, a region defined as >1 
m above the seafloor, reacted the most to either vehicle 
(22% to the submersible and 73% to the ROV). Squares- 
pot and Blue Rockfishes represented 80% of the midwa- 
ter reactions to the submersible, and Halfbanded and 
Pygmy Rockfishes accounted for 90% of the reactions 
of midwater fishes to the ROV. This pattern of greater 
percentage of reactions with increased height off the 
seafloor was observed for most individual taxa. Even 
those species that are primarily demersal, like Cowcod 
and Greenstriped (S. elongatus) and Greenspotted (S. 
chlorostictus) Rockfishes, exhibited this pattern in ob- 
servations from both the submersible and ROV. 
The fishes that demonstrated any type of reaction 
to each vehicle primarily swam away rather than to- 
ward the vehicles (Fig. 4; Table 3, A and B). Only a 
small percentage (0-8%) of fishes swam toward ei- 
ther vehicle; most of these fishes were Bocaccio near 
the seafloor, and 19 of 50 of those Bocaccio reacted by 
swimming toward the submersible. Most fishes either 
moved away (forward, ahead of the vehicle) or sideways 
(to the left or right). However, 37% of all fishes in the 
midwater reacted by swimming downward when ini- 
tially encountered by the submersible (Table 3A). This 
group was dominated by Blue, Widow (S. entomelas), 
and Splitnose ( S . diploproa) Rockfishes (representing 
96% of those midwater fishes that reacted by swim- 
ming down). Only 13% of all fishes near the seafloor 
moved downward as the submersible approached; Bo- 
caccio and Widow Rockfish reacted the most in this 
category (20% and 25% of all fish that reacted, respec- 
tively). Only 1% of fishes in the midwater or near the 
seafloor reacted to the ROV by swimming downward 
(Table 3B). 
The distance at which a fish reaction occurred var- 
ied between vehicles (Table 4; Fig. 5). Blue, Halfband- 
ed, Widow, Bank (S. rufus), and Splitnose Rockfishes 
moved at distances >3 m in front of the submersible. 
These species often were located in the midwater or 
near the seafloor. However, some species located most 
often near the seafloor (e.g., Bocaccio and Canary and 
Squarespot Rockfishes) reacted more often when the 
vehicle came closer to them (<3 m). Seafloor-dwelling 
species did not react often to the submersible, and, 
when they did, there was no clear pattern in reactions 
related to distance in front of the vehicle. The species 
that reacted farthest in front of the ROV were Half- 
banded, Widow, and Yellowtail Rockfishes, all of which 
were found near the seafloor or in the midwater. Spe- 
cies that reacted closer (<3 m) to the ROV included 
fishes living almost entirely on the seafloor (e.g.. Black- 
eye Goby, Shortspine Combfish [ Zaniolepis frenata], 
and Greenstriped Rockfish), as well as some near the 
seafloor and in the midwater (e.g., Bocaccio and Ca- 
nary, Greenspotted, Rosy [S. rosaceus], Splitnose, and 
Squarespot Rockfishes). 
Body length was determined for all fishes that were 
observed during the submersible surveys (n = 10,550), 
but only 9177 fishes (57%) of all fishes observed in 
video footage from the ROV surveys were measured. 
Total length ranged from 5 to 100 cm for fishes ob- 
served from the submersible and from 5 to 70 cm for 
fishes seen during the ROV surveys. Most fishes were 
