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Fishery Bulletin 1 13(1) 
Figure 3 
Photographs of scour marks created by doors of the bottom trawl used in this study conducted off central California. 
Images were taken (A) in November 2009, immediately after low-intensity trawling, and (B) in September 2010, 1 year 
after low-intensity trawling. 
pling periods and seasons (Figs. 2, A-F). The densities 
of polychaete worms (Fig. 2A) peaked during 3 separate 
sampling periods during 2 separate seasons; the larg- 
est peak (480 individuals m _2, occurred in September 
2009, followed by smaller peaks in May 2011 (430 indi- 
viduals m-2) and May 2012 (390 individuals m-2). No 
polychaetes were observed in either November 2009 or 
November 2010. Occurrence of brittle stars (Fig. 2B) 
was observed at much lower densities. For example, 
absent from the study area in September and Novem- 
ber 2009, brittle stars were present during every other 
sampling period, peaking at 60 individuals m-2 in Sep- 
tember 2011. Other organisms, including notaspideans 
(Fig. 20, octopods (Fig. 2D), teuthids (Fig. 2E), and as- 
teroids (Fig. 2F) were present in very small, although 
variable, densities over the course of our study. 
In the broader study area, the north reference site 
(Fig. 1) had an assemblage of sessile invertebrates that 
was similar to the assemblage in the primary study 
area, including sea whips ( Halipteris spp.), sea pens 
( Ptilosarcus gui'neyi, Pennatula spp., and Stylatula 
spp.), and anemones (Halcampidae, Urticina spp., and 
Pachycerianthus fimbriatus). The south reference site 
had invertebrates that were more mobile, primarily 
ocean shrimp ( Pandalus jordani), that were rarely ob- 
served in the study plots. However, it should be noted 
that the amount of recent trawling effort in the north 
and south reference sites was unknown. 
Low-intensity trawling 
Trawl doors can create scour marks (or troughs) in the 
sediment as they are towed along the bottom of the 
seafloor. Scour marks from the low-intensity trawling 
effort were clearly evident in the sediment immediate- 
ly after the directed trawling (Fig. 3A) and were still 
present 1 year after trawling in September 2010 (Fig. 
3B). Demersal fishes, mobile invertebrates, and drift 
kelp were all observed in and immediately adjacent to 
these scour marks. 
The mean percent cover of microtopographic fea- 
tures was similar between the trawled and control 
plots in September 2009 before the directed trawling, 
at 75% and 72%, respectively (Fig. 4A). Immediately 
following the low-intensity trawling treatment, the 
percent cover of microtopographic features in control 
and trawled plots diverged but did not differ statis- 
tically (Z=0.109, P=0.460). The mean percent cover of 
microtopographic features in the trawled plots declined 
by 15%. Interestingly, the percent cover also declined 
after trawling in the control plots, although by an 
amount (9%) lower than the decrease in the trawled 
plots. The small but insignificant difference in complex- 
ity (Z=0.096, P=0.464) between trawled and control 
plots persisted at 6 months after trawling, but values 
in both types of plots stabilized. In August 2010, at 1 
year after trawling, the mean percent cover of micro- 
topographic features declined in both groups of plots 
over the 6-month period (15% and 17% in control and 
trawled plots, respectively) but were not significantly 
different (Z=0.156, P=0.440). The cumulative decline in 
mean percent cover at 1 year after trawling was -24% 
and -31% in control and trawled plots, respectively. 
The densities of both sessile, structure-forming (Fig. 
4B) and mobile (Fig. 4C) macro-invertebrates were very 
low in both trawled and control plots before and after 
