84 
Fishery Bulletin 1 13(1) 
building efforts for overfished stocks and has resulted 
in displacement of some trawling effort (Bellman et al., 
2005). Federal closures for trawl fishing in additional 
areas were established in 2006 to protect essential fish 
habitat (Copps et ah, 2008; Gleason et ah, 2013). To- 
gether, these closures to trawling protect 61% of shelf 
and slope habitat from bottom trawling in central Cali- 
fornia, between Point Conception and Point Reyes from 
the shore to a depth of 2000 m). 
In this study, we collaborated with members of the 
commercial fishing industry to conduct experimental 
trawling with small-footrope gear at known intensities 
in the unconsolidated sediments of the outer continental 
shelf off Point Buchon and Morro Bay in central Califor- 
nia. This directed trawling allowed us to quantify, with 
a high degree of confidence, the impacts to physical and 
biological attributes of fish habitat in the study area. 
Materials and methods 
Data collection 
The primary study area was located on the outer con- 
tinental shelf off Point Buchon and Morro Bay (Fig. 
1). This study area was selected after discussions with 
members of the commercial fishing industry in Morro 
Bay and was situated immediately shoreward of the 
federal RCA at the shelf-slope break in a location 
that was historically trawled for flatfish, such as the 
petrale sole (Eopsetta jordani ) and Dover sole (Micro- 
stomus pacificus). The study area had not been trawled 
commercially since before 2000, according to vessel 
monitoring system data (Mason 1 ; Mason et al., 2012). 
Prospecting with an ROV in 2008 and multibeam sonar 
in 2009 revealed that the area comprises low-relief, un- 
consolidated sediments. Our study was conducted be- 
tween 2009 and 2012; in 2012, additional surveys were 
conducted with an ROV along transects to the north 
and south of the study area to compare different sub- 
strates and biological communities at other locations 
along the shelf (Fig. 1). 
Along the 170-m isobath, 8 paired study plots were 
identified (Fig. 1). Each plot measured approximately 
1000 m by 300 m, and 500 m separated each adjacent 
plot. Plots were numbered from 1 to 8 consecutively 
from north to south; plots 3, 4, 7, and 8 were experi- 
mentally trawled plots, and plots 1, 2, 5 and 6 were 
untrawled (or control) plots. 
Experimental trawling 
All trawling activities were conducted aboard FV South 
Bay, a 16.8-m trawler that operated from Morro Bay. 
The South Bay was equipped with a bottom trawl that 
had a small footrope, in accordance with gear require- 
1 Mason, J. 2008. Personal commun. Pacific Fisheries Envi- 
ronmental Laboratory, Southwest Fisheries Science Center, Na- 
tional Marine Fisheries Service, NOAA, Pacific Grove, CA 93950. 
ments under federal regulations for trawling shoreward 
of the RCA. The trawl design consisted of a 2-bridle 
trawl with a fishing circle of 300 meshes and a mesh 
size of 11.6 cm. The funnel tapered down to the co- 
dend at a 2:1 cutting ratio, and the mesh size at the 
codend was 11.4 cm. The footrope was configured with 
“mudgear” discs that measured 20.3 and 10.2 cm in di- 
ameter. The larger 20.3-cm-diameter discs were spaced 
evenly along the footrope at 1-m intervals, allowing the 
smaller 10.2-cm-diameter discs to ride above the sea- 
floor. The net was held open by trawl doors, each mea- 
suring 1.1 by 1.4 m and weighing approximately 315 
kg. Trawling operations were conducted at a speed of 
2.1 knots, which is the speed typically used to harvest 
most flatfishes and soles (Bothidae and Pleuronectidae) 
in the federal groundfish fishery. An exception to this 
typical speed is that speeds of 3. 0-4.0 knots are used to 
harvest California halibut (Paralichthys californicus) in 
the state-managed fishery for that particular species. At 
the speed used for this study, the trawl doors spread the 
net width to 55 m and the net height to 2.4 m. 
Experimental trawling operations were divided into 
2 treatments according to intensity of effort: low inten- 
sity and high intensity. The 2 treatments were designed 
to broadly reflect the range of effort applied histori- 
cally to the seafloor in the study area, on the basis of 
published records (Mason et al., 2012) and unpublished 
data collected by NOAA Fisheries (Mason 1 ). The num- 
ber of trawl passes per treatment was calculated by 
using the width of the study plots and the width of the 
trawl doors on the seafloor when underway. The low- 
intensity treatment (October 2009) featured enough 
passes through the study plots to ensure that every 
square meter of each plot was trawled 3 times. The 
high-intensity treatment (October 2010) doubled that 
effort on the same plots so that each plot was impacted 
an additional 5 times, for a total of 8 passes. For lo- 
gistical reasons, the high-intensity trawling effort was 
applied to the previously trawled plots and, therefore, 
reflects 2 years of directed trawling. To minimize the 
number of times the trawl gear was deployed and re- 
covered during each treatment and to avoid accidental- 
ly trawling in control plots, adjacent plots were paired 
such that the trawl would remain on the seafloor from 
the beginning of plot 3 to the end of plot 4, and the 
same protocol followed at plots 7 and 8 (Fig. 1). 
Imagery collection 
Video and still imagery of the seafloor were collected 
with a Vector L4 ROV (Deep Ocean Engineering, Inc., 
San Jose, CA) equipped with 3 georeferenced cameras 
(forward-looking video, down-looking video, and digi- 
tal still camera), 2 quartz halogen and 2 hydrargyrum 
medium-arc iodide lights, paired forward- and down- 
looking lasers, and a strobe for enhancement of still 
photographs. The ROV was also equipped with an al- 
timeter and forward-facing multibeam sonar. The posi- 
tion of the ROV on the seafloor was maintained with 
