54 
Reactions of fishes to two underwater survey 
tools, a manned submersible and a remotely 
operated vehicle 
Email for address for contact author: tom.laidig@noaa.gov 
Abstract — We examined the reac- 
tions of fishes to a manned submers- 
ible and a remotely operated vehicle 
(ROV) during surveys conducted in 
habitats of rock and mud at depths 
of 30-408 m off central California 
in 2007. We observed 26 taxa for 
10,550 fishes observed from the 
submersible and for 16,158 fishes 
observed from the ROV. A reaction 
was defined as a distinct movement 
of a fish that, for a benthic or hover- 
ing individual, was greater than one 
body length away from its initial po- 
sition or, for a swimming individual, 
was a change of course or speed. Of 
the observed fishes, 57% reacted to 
the ROV and 11% reacted to the 
submersible. Aggregating species 
and those species initially observed 
off the seafloor reacted most often to 
both vehicles. Fishes reacted more 
often to each vehicle when they 
were >1 m above the seafloor (22% 
of all fishes >1 m above the seafloor 
reacted to the submersible and 73% 
to the ROV) than when they were 
in contact with the seafloor (2% of 
all reactions to the submersible and 
18% to the ROV). Fishes reacted by 
swimming away from both vehicles 
rather than toward them. Consider- 
ation of these reactions can inform 
survey designs and selection of sur- 
vey tools and can, thereby, increase 
the reliability of fish assemblage 
metrics (e.g., abundance, density, 
and biomass) and assessments of 
fish and habitat associations. 
Manuscript submitted 16 February 2012. 
Manuscript accepted 15 November 2012. 
Fish. Bull. 111:54-67 (2013). 
doi: 10. 7755/FB. 111.1.5 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessar- 
ily reflect the position of the National 
Marine Fisheries Service, NOAA. 
Thomas E. Laidig (contact author) 
Lisa M. Krigsman 
Mary M. Yoklavich 
Fisheries Ecology Division 
Southwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
110 Shaffer Road 
Santa Cruz, California 95060 
Visual surveys of fishes in deep wa- 
ter and untrawlable areas have been 
conducted more frequently in re- 
cent years than in the past largely 
because of increased availability of 
underwater vehicles and the need 
for nonextractive assessments, par- 
ticularly in no-take areas. These 
vehicles have provided researchers 
with the opportunity to gather valu- 
able information on species composi- 
tion, habitat associations, population 
density, and various behavioral traits 
that was previously unattainable 
in these deep (>30 m), structurally 
complex areas (Carlson and Straty, 
1981; Pearcy et ah, 1989; Yoklavich 
et ah, 2007; Laidig et ah, 2009; Love 
et ah, 2009). Visual surveys present 
advantages over traditional sampling 
methods (e.g., trawling, hook and 
line, traps) through the use of non- 
destructive, in situ observations of 
fishes in their natural habitats. 
One concern in counting fishes is 
their reaction to an observer (e.g., 
in scuba or snorkel surveys) or un- 
derwater vehicle (e.g., submersibles, 
remotely operated vehicles [ROVs], 
and camera sleds; Stoner et ah, 
2008). The vehicles, in particular, can 
produce a number of electronic and 
mechanical stimuli (e.g., lights, mo- 
tion, and noise) that could alter be- 
havior (Krieger, 1993; Uiblein et ah, 
2003; Ryer et ah, 2009). Accounting 
for these reactions is an important 
aspect of accurate population assess- 
ments. To this end, Yoklavich et ah 
(2007) quantified the reactions of 
fishes to a manned submersible dur- 
ing a survey of Cowcod ( Sebastes le- 
uis). Cowcod were found to react very 
little to the submersible, and that low 
level of reaction strengthened the ac- 
curacy of the survey results and as- 
sociated stock assessment. Other 
studies have reported fish reactions 
to both ROVs (Johnson et ah, 2003; 
Trenkel et ah, 2004a; Lorance and 
Trenkel, 2006) and manned submers- 
ibles (Murie et ah, 1994; Krieger and 
Sigler, 1996; Gibbons et ah, 2002). 
However, most of these studies were 
qualitative, simply noting that fishes 
moved out of the way of the vehicles. 
More quantitative studies are needed 
to improve our understanding of the 
nature and magnitude of reactions 
of various fish species to a variety of 
underwater survey vehicles. 
The goal of our study was to char- 
acterize the reactions of a wide range 
of marine fish species to 2 commonly 
used underwater vehicles (a manned 
submersible and an ROV) during 
surveys conducted along the seafloor. 
We quantified the degree of species- 
and size-specific reactions of fishes 
living both on and above the seafloor. 
