Laidig et al Reactions of fishes to a manned submersible and a remotely operated vehicle 
57 
mounted 20 cm apart on either side of the color vid- 
eo camera and were visible to the observer inside the 
submersible. For both vehicles, fishes were measured 
to the nearest 5 cm. Five lasers were mounted on the 
front of the ROV; these lasers included 2 pairs of par- 
allel lasers (20 and 60 cm apart) and a single crossing 
laser used to determine depth of field. The laser spots 
on the video footage were used in postsurvey analysis 
to estimate both the size (total length) of fishes and the 
distance ahead of the ROV at which a fish reaction oc- 
curred. An effort was made to measure all fishes; how- 
ever, some fishes were either too far away or partially 
obscured, and, therefore, they could not be measured. 
In an important distinction in survey methodology 
between the 2 vehicles, the scientific observer inside 
the submersible identified, counted, and estimated 
length of fishes (as annotated on the audio channel of 
the video camera), but these tasks were performed only 
with video footage from the ROV surveys. Video foot- 
age from both vehicles was reviewed after completion 
of the surveys. Fishes in both surveys were identified 
to the lowest possible taxon with taxonomic keys (Love 
et al. [2002] for rockfishes, and Miller and Lea [1972] 
and Eschmeyer et al. [1983] for the remaining fishes). 
All fish reactions were determined solely from video 
footage of the forward-facing cameras on both vehicles 
in order for the methods to be similar between survey 
vehicles. A reaction was defined as a distinct movement 
of a fish if that movement was greater than one body 
length away from the initial position of the fish. Some 
fishes that were hovering off the seafloor would turn 
and face the vehicle as it passed by, but this movement 
was not considered a reaction unless a fish actively 
swam at least one body length in any direction. If a 
fish was swimming in a particular direction when first 
observed and continued swimming in the same direc- 
tion at the same speed during the entire time on video, 
that fish was considered to have no reaction. However, 
a reaction was noted if a fish changed course or swim- 
ming speed. 
The initial position of a fish was recorded as 1 of 
3 categories: resting on the seafloor, <1 m above the 
seafloor (but not touching the seafloor), or >1 m above 
the seafloor. Direction of fish reaction was recorded as 
swimming 1) toward the vehicle, 2) parallel, forward, 
and away from the vehicle, 3) perpendicular to the left, 
4) perpendicular to the right, or 5) down toward the 
seafloor. No fishes were ever recorded moving upward. 
We used time and an average vehicle speed of 0.5 m/s to 
estimate the distance between a reacting fish and the 
front of the Delta submersible. The distance between a 
reacting fish at first sighting and the front of the ROV 
was estimated with the laser array. This distance was 
binned to <3 m or 3-6 m. A 20-cm fish could be seen at 
a maximum distance of about 6 m in front of the ROV 
and about 9 m in front of the submersible (because im- 
ages could be distinguished farther with the low-light, 
monochrome camera on the submersible compared with 
the color camera on the ROV). To ensure that results 
from the ROV and submersible were comparable, we 
used data only from fishes that occurred at a distance 
of at most 6 m from the submersible. 
Hagfishes ( Eptatretus spp. ), thornyheads ( Sebastolo - 
bus spp.), and young-of-the-year (YOY) rockfishes ( Se - 
bastes spp.) were included as taxonomic groups in our 
analyses. Hagfishes often were seen hiding in holes or 
under structure and could not be identified to species. 
However, all the hagfishes that could be identified were 
Pacific Hagfish (Eptatretus stoutii). The thornyhead 
group comprised Shortspine Thornyhead ( Sebastolobus 
alascanus), a few Longspine Thornyhead (S. altivelis ; 1 
observed from the submersible and 4 from the ROV), 
and mostly unidentified thornyheads. YOY rockfishes 
were a mix of many species, and each was recorded as 
5 cm in total length. 
We determined fish reactions only while the vehi- 
cles traveled forward in survey mode. No fish reactions 
were counted if the seafloor, which we used as a sta- 
tionary reference for fish movement, was not observed 
in the video footage for >5 s (as when either vehicle 
transited over narrow ravines or when the ROV was 
pulled off transect by the ship). A number of species 
were not considered in our analyses. For instance, pe- 
lagic schooling fishes, such as Northern Anchovy (En- 
graulis mordax). Jack Mackerel ( Trachurus symmetri- 
cus ), and Pacific Chub Mackerel ( Scomber japonicus), 
swam around the vehicles for extended periods of time 
(possibly because they were attracted to the vehicles, 
but this idea was not verified), and these long periods 
of time increased the possibility that fishes would be 
double counted. These species also darted in and out of 
the view of the cameras, making it difficult to assess 
individual reactions to the vehicles. Only species that 
accounted for >1% of the total number of fish observed 
from either vehicle were included in the analyses of 
reactions to the vehicles. A chi-square test was used to 
evaluate reactions relative to initial fish position. 
Results 
A total of 223 transects (56 h) were surveyed with 
the Delta submersible in hard (70% rock, boulder, and 
cobble) and soft (30%) mud and sand) seafloor habitat, 
and 10,550 fishes were observed (Table 1). A total of 
10 ROV dives (21 h) were conducted, and 16,158 fishes 
were observed. Although the ROV covered only a subset 
of all submersible dives, the type of habitats surveyed 
with the ROV (60% hard and 40% soft) were similar to 
those habitats surveyed with the submersible. Water 
visibility during submersible dives ranged from 4 to 13 
m (as estimated by the submersible pilot during each 
dive), averaged 8 m, and was greatest at depths >100 
m. Observations made from the submersible were lim- 
ited more by light penetration from the submersible (9 
m) than by water visibility. Observations made from 
the ROV video footage were confined to ~6 m, because 
