82 
NOAA 
National Marine 
Fisheries Service 
Abstract— Bottom trawling has been 
shown to affect the seafloor and 
associated biological communities 
around the world. Considerably less 
is known about the dynamics of im- 
pacts to structural attributes of fish 
habitat, particularly in unconsoli- 
dated sandy sediments of the con- 
tinental shelf. We collaborated with 
commercial fishermen to conduct 
experimental trawls, with the type 
of small-footrope trawl required for 
trawling on the continental shelf, 
along the 170-m isobath in an area 
off Morro Bay in central California. 
The bottom trawling intensity we 
applied was based on the historical 
range of fishing effort in the study 
area and included low-intensity and 
high-intensity treatments. A remote- 
ly operated vehicle was used to col- 
lect continuous video and still photo- 
graphs in trawled and in untrawled 
control plots, before trawling and at 
2 weeks, 6 months, and 1 year af- 
ter trawling. Scour marks from the 
heavy doors of the trawl were ob- 
served in the seafloor and persisted 
for at least a year. Although data 
extracted from the collected imag- 
ery showed some smoothing of the 
seafloor in trawled plots, the mini- 
mal differences between trawled and 
control plots in microtopographic 
structure on the seafloor were sta- 
tistically significant only during one 
sampling period. Further, there were 
no significant differences between 
trawled and untrawled plots with 
respect to structure-forming inver- 
tebrates (e.g., sea whips) and mobile 
invertebrates (e.g., sea stars). The 
results of our study, part of ongoing 
efforts to understand and manage 
fishing impacts, indicate that bottom 
trawling with a small-footrope gear 
may have limited effects in some 
sand habitats. 
Manuscript submitted 28 August 2013. 
Manuscript accepted 12 December 2014. 
Fish. Bull. 113:82-96 (2015). 
doi: 10.7755/FB.113.1.8 
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. 
Fishery Bulletin 
a- established 1881 ■<?. 
Spencer F. Baird 
First U S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Ecological effects of bottom trawling on 
the structural attributes of fish habitat in 
unconsolidated sediments along the central 
California outer continental shelf 
James Lindholm 1 
Mary Gleason 2 
Donna Kline 1 
Larissa Clary 1 
Steve Rienecke 2 
Alii Cramer 1 
Marc Los Huertos 3 
Email address for contact author: |lindholm@csumb.edu 
1 Institute for Applied Marine Ecology 
California State University Monterey Bay 
100 Campus Center 
Seaside, California 93955 
2 The Nature Conservancy 
99 Pacific Street, Suite 200G 
Monterey, California 93940 
3 Environmental Analysis Program 
Pomona College 
185 East 6th Street 
Claremont, California 91711 
The ecological effects of bottom 
trawling on continental shelves have 
been documented in several regions 
of the world (see reviews in Day- 
ton et ah, 1995; Kaiser et ah, 1998; 
Watling and Norse, 1998; Auster and 
Langton, 1999; NRC, 2002). These ef- 
fects include overfishing (NRC, 1999; 
Jackson et ah, 2001) and bycatch 
(Alverson et ah, 1994; De Alteris et 
al., 2000; Machias et ah, 2001; An- 
derson and Clark, 2003), as well 
as impacts to structural attributes 
of the seafloor (Auster et ah, 1996; 
Lindholm et ah, 2004). Indeed, bot- 
tom trawling has been described as 
the most significant impact on ma- 
rine ecosystems below the effective 
depth of storm penetration (Dayton 
et ah, 1995; Watling and Norse, 1998; 
NRC, 2002). 
In the context of impacts to the 
seafloor, it has been established that 
bottom trawling can smooth bed- 
forms (Hall, 1994; Schwinghamer et 
ah, 1998), remove structure-form- 
ing invertebrate fauna (the bodies 
of such organisms provide habitat 
structure) (Auster et ah, 1996; Col- 
lie et ah, 1997; Kaiser et ah, 2000; 
Koslow et ah, 2001), and remove 
structure-building organisms that 
create habitat (such as depressions 
in the sediment), as a result of their 
normal behavior (Auster and Lang- 
ton, 1999). Bedforms and habitat fea- 
tures formed or created by organisms 
are used by fishes at a variety of life 
history stages as refugia from preda- 
tors and bottom currents (Auster et 
ah, 1991; Auster and Langton, 1999; 
Stoner and Titgen, 2003). 
Observations of the use of sand- 
wave habitats on Georges Bank and 
