332 
Abstract — Rockfishes ( Sebastes spp.) 
are an important component of 
North Pacific marine ecosystems 
and commercial fisheries. Because 
the rocky, high-relief substrate that 
rockfishes often inhabit is inacces- 
sible to standard survey trawls, pop- 
ulation abundance assessments for 
many rockfish species are difficult. 
As part of a large study to classify 
substrate and compare complemen- 
tary sampling tools, we investigated 
the feasibility of using an acoustic 
survey in conjunction with a lowered 
stereo-video camera, a remotely oper- 
ated vehicle, and a modified bottom 
trawl to estimate rockfish biomass 
in untrawlable habitat. The Snake- 
head Bank south of Kodiak Island, 
Alaska, was surveyed repeatedly over 
4 days and nights. Dusky rockfish 
(S. variabilis), northern rockfish (S. 
polyspinis), and harlequin rockfish (S. 
variegatus) were the most abundant 
species observed on the bank. Back- 
scatter attributed to rockfish were 
collected primarily near the seafloor 
at a mean height off the bottom of 1.5 
m. Total rockfish backscatter and the 
height of backscatter off the bottom 
did not differ among survey passes or 
between night and day. Biomass esti- 
mates for the 41 square nautical-mile 
area surveyed on this small, predomi- 
nantly untrawlable bank were 2350 
metric tons (t) of dusky rockfish, 331 
t of northern rockfish, and 137 t of 
harlequin rockfish. These biomass 
estimates are 5-60 times the density 
estimated for these rockfish species 
by a regularly conducted bottom trawl 
survey covering the bank and the sur- 
rounding shelf. This finding shows 
that bottom trawl surveys can under- 
estimate the abundance of rockfishes 
in untrawlable areas and, therefore, 
may underestimate overall population 
abundance for these species. 
Manuscript submitted 18 November 2011. 
Manuscript accepted 23 May 2012. 
Fish. Bull. 110:332-343 (2012). 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Evaluation of rockfish abundance 
in untrawlable habitat: combining acoustic 
and complementary sampling tools 
Darin T. Jones (contact author ) 1 
Christopher D. Wilson 1 
Alex De Robertis 1 
Christopher N. Rooper' 
Thomas C. Weber 2 
John L. Butler 3 
Email address for contact author: darin.|ones@noaa gov 
1 Alaska Fisheries Science Center 
National Marine Fisheries Service 
7600 Sand Point Way NE 
Seattle, Washington 98115 
2 Center for Coastal and Ocean Mapping 
University of New Hampshire 
24 Colovos Road 
Durham, New Hampshire 03824 
3 Southwest Fisheries Science Center 
National Marine Fisheries Service 
3333 North Torrey Pines Court 
La Jolla, California 92037 
Many fish species associate with and 
find refuge in high-relief substrate, 
where bottom trawl surveys are inef- 
fective (O’Connell and Carlile, 1993; 
Yoklavich et ah, 2000; Zimmermann, 
2003). The bottom trawl survey of the 
Gulf of Alaska (GOA) conducted by 
researchers with the NOAA Alaska 
Fisheries Science Center (AFSC) 
(von Szalay et ah, 2010) routinely 
encounters areas that are untrawlable 
because of rough substrate or known 
hazards to fishing gear on the sea- 
floor. When untrawlable substrate is 
located at a designated sampling sta- 
tion, an alternate location with suit- 
able substrate is sought nearby (von 
Szalay et ah, 2010). Mean estimates of 
species abundance from sampling sta- 
tions are then extrapolated over the 
entire management area, including 
known untrawlable areas. Yet rock- 
fish abundance between trawlable and 
untrawlable areas can vary consid- 
erably (Stein et ah, 1992; Jagielo et 
ah, 2003; Rooper et ah, 2007) and is 
often lower in trawlable areas than 
in untrawlable areas (O’Connell and 
Carlile, 1993; Rooper et ah, 2010). 
Therefore, extrapolated estimates can 
be inaccurate. 
In habitats that cannot be sam- 
pled adequately with trawls, acoustic 
methods combined with complementa- 
ry sampling tools may improve rock- 
fish stock assessments by providing 
more complete and accurate estimates 
of rockfish populations. Acoustic sur- 
veys can cover large areas and much 
of the water column in a relatively 
short time, but accurate abundance 
estimates require consideration of the 
target species, their diel movements 
and association with the seafloor, 
and the type and structure of the 
substrate. It has been demonstrated 
that acoustic surveys can be success- 
fully used to assess pelagic rockfish 
populations in areas of relatively low 
relief (Wilkins, 1986; Richards et ah, 
1991; Stanley et ah, 2000; Krieger 
et ah, 2001). Cooke et ah (2003) de- 
scribed methods for acoustically sam- 
pling fishes in areas of high relief by 
performing multiple passes at vari- 
ous angles to thoroughly map the sea- 
floor. However, when fish are on or 
near the bottom in the acoustic dead 
