30 
Effects of trawling for ocean shrimp 
( Panda/us jordani ) on macroinvertebrate 
abundance and diversity 
at four sites near Nehalem Bank, Oregon 
Robert W. Hannah (contact author ) 1 
Stephen A. Jones' 
William Miller 1 
Jayme S. Knight 2 
Email address for contact author: bob.w.hannah@state.or.us 
1 Oregon Department of Fish and Wildlife 
Hatfield Marine Science Center 
2040 SE Marine Science Drive 
Newport, Oregon 97365 
2 Alaskan Observers, Inc. 
130 Nickerson, #206 
Seattle, Washington 98109 
Abstract — Surveys with a remotely 
operated vehicle (ROV) at four mud- 
habitat sites with different histories 
of ocean shrimp (Pandalus jordani) 
trawling showed measurable effects of 
trawling on macroinvertebrate abun- 
dance and diversity. Densities of the 
sea whip (Halipteris spp., P<0.01), 
the flat mud star ( Luidia foliolata, 
P<0.001), unidentified Asteroidea 
(.PcO.OS), and squat lobsters (unidenti- 
fied Galathoidea, P<0.001) were lower 
at heavily trawled (HT) sites, as was 
invertebrate diversity based on the 
Shannon-Wiener index. Sea cucum- 
bers (unidentified Holothuroidea) 
and unidentified corals (Hydrocora- 
lia) were observed at lightly trawled 
(LT) sites but not at HT sites. Hag- 
fish ( Eptatretus spp.) burrows were 
the dominant structural feature of 
the sediment surface at all sites and 
were more abundant at the HT sites 
(P<0.05), a result potentially related 
to effects from fishery discards. Sub- 
stantial heterogeneity was found 
between the northern and southern 
site pairs, indicating high site-to-site 
variability in macroinvertebrate den- 
sities in these deep (146-156 m) mud 
habitats. Two of the study sites were 
closed to trawling in June 2006. The 
data from this study can be used in 
combination with future surveys to 
measure recovery rates of deep, mud, 
seafloor habitats from the effects of 
trawling, thus providing a critical 
piece of information for ecosystem- 
based management. 
Manuscript submitted 24 April 2009. 
Manuscript accepted 17 September 2009. 
Fish. Bull. 108:30-38 (2010). 
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. 
Intensive fishing with bottom trawls 
and dredges can have significant 
effects on some types of seafloor 
habitats (Auster et al., 1996; Collie 
et al., 1997). The reduction in habi- 
tat complexity that can result from 
trawling is of particular concern 
because of the potential for reduc- 
tions in fish production at impacted 
sites (Lindholm et al., 1999). In con- 
tinental shelf waters off the United 
States west coast (excluding Alaska), 
the effect of mobile fishing gears on 
seafloor habitats has received very 
little study. The research that has 
been conducted has focused on effects 
from otter trawls used to harvest 
groundfish (Engel and Kvitek, 1998; 
Hixon and Tissot, 2007). However, 
the principal trawl fishery currently 
operating on soft-bottom habitats on 
the outer continental shelf in these 
waters is the fishery for ocean shrimp 
( Pandalus jordani). Habitat impacts 
from ocean shrimp trawls are likely 
to be different from those from 
groundfish trawls (Gibbs et al., 1980; 
Kaiser et al., 2002). Ocean shrimp 
trawls are considered to be semipe- 
lagic gear: they comprise a footrope 
system that incorporates a chain or 
cable groundline partially covered 
with 6.4-cm diameter rubber discs, 
but are configured to elevate the fish- 
ing line of the net about 35-70 cm 
above the bottom (Hannah and Jones, 
2000, 2003). No studies of the physi- 
cal effects of ocean shrimp trawling 
on the seafloor ecosystem have been 
conducted. We report here on the first 
such study examining the condition 
of mud-seafloor habitats in the areas 
primarily impacted by ocean shrimp 
trawling. 
The lack of research on the effects 
of trawling on some U.S. west coast 
seafloor habitats has been caused, 
in part, by a lack of suitable control 
sites that have not been previously 
trawled (Engel and Kvitek, 1998). 
However, some of the areas of rocky 
habitat that have been recently 
closed to trawling also contain lim- 
ited sections of soft-bottom habitat 
that have been historically trawled, 
but that are now closed to trawling. 
The closure of these areas creates an 
opportunity to study habitat impacts 
from chronic trawling by examining 
how these areas recover after clo- 
sure, in comparison to nearby areas 
of similar habitat that continue to be 
trawled. One such area is a section 
of mud habitat that has historically 
been trawled for ocean shrimp but 
is now enclosed within the Nehalem 
Bank Essential Fish Habitat no- 
trawl zone (Fig. 1) that was closed 
to trawling in June 2006. One objec- 
tive of this study was to conduct an 
