Hannah et al.: Effects of shrimp trawling on macroinvertebrate abundance and diversity 
35 
Table 2 
Mean densities (number/ha) and standard errors (SE) of epibenthic macroinvertebrates (pandalid shrimp excluded) and fish at 
four mud-habitat sites with different histories of ocean shrimp ( Pandalus jordani ) trawling off the northern Oregon coast (see 
Fig. 1). P-value shown is for the effect of trawling history (lightly or heavily trawled) on density in a two-factor analysis of vari- 
ance on Box-Cox transformed data (ns=nonsignificant at P> 0.05, nt=not tested, nm=not meaningful). 
Taxon 
Density (number/ha) 
1A 
IB 
2A 
2B 
Mean 
SE 
Mean 
SE 
Mean 
SE 
Mean 
SE 
P-value 
Invertebrates 
Halipteris spp. (sea whips) 
452.9 
51.2 
459.5 
46.9 
190.1 
10.0 
60.4 
11.8 
0.0025 
Ptilosarcus gurneyi (orange sea pen) 
141.8 
48.6 
100.8 
9.2 
26.9 
9.7 
14.5 
4.1 
ns 
Stylasterias forreri (fish-eating star) 
21.1 
3.4 
28.0 
6.7 
19.8 
3.9 
28.0 
7.4 
ns 
Luidia foliolata (flat mud star) 
28.8 
4.1 
9.7 
1.9 
27.2 
3.5 
7.8 
2.8 
0.0001 
Unidentified Asteroidea (sea stars) 
3.3 
1.0 
4.2 
1.9 
6.8 
0.9 
2.0 
2.0 
0.0236 
Brisaster spp. (heart urchins) 
103.6 
42.9 
44.8 
7.1 
92.6 
14.1 
96.4 
14.9 
ns 
Cancer magister (Dungeness crab) 
2.9 
1.4 
2.5 
1.0 
9.0 
3.7 
4.5 
3.1 
ns 1 
Unidentified Ophiuroidea (basket stars) 
7.9 
2.9 
4.9 
1.6 
0.0 
nm 
0.0 
nm 
nt 
Unidentified Galatheoida (squat lobsters) 
2.0 
0.9 
0.8 
0.8 
92.0 
10.9 
4.5 
3.1 
0.0003 
Rossia spp. (bobtail squid) 
2.4 
1.2 
3.2 
1.9 
3.9 
2.1 
2.0 
2.0 
nt 
Unidentified Octopodidae 
0.0 
nm 
0.0 
nm 
0.0 
nm 
0.7 
0.7 
nt 
Unidentified anemone 
6.7 
4.0 
2.5 
1.0 
0.0 
nm 
0.0 
nm 
nt 
Unidentified corals (Hydrocoralia) 
1.4 
1.4 
0.0 
nm 
0.9 
0.9 
0.0 
nm 
nt 
Unidentified Echinoida (sea urchins) 
1.4 
1.4 
0.0 
nm 
23.6 
13.2 
2.0 
2.0 
nt 
Unidentified Holothuroidea (sea cucumbers) 
0.6 
0.6 
0.0 
nm 
11.9 
2.0 
0.0 
nm 
nt 
Unidentified invertebrates 
2.0 
0.9 
0.9 
0.9 
6.4 
2.7 
2.9 
1.9 
nt 
Fishes 
Unidentified flatfish 
359.1 
44.4 
315.7 
24.8 
322.3 
22.2 
458.7 
34.4 
ns 
Merluccius productus (Pacific hake) 
143.8 
65.6 
188.6 
18.1 
340.3 
19.7 
269.0 
47.6 
ns 
Zoarcidae (eelpouts) 
341.3 
41.4 
101.4 
13.9 
325.3 
52.0 
337.6 
74.5 
0.0051 
Sebastes spp. (rockfishes) 
55.7 
9.0 
20.9 
7.8 
94.1 
16.7 
62.2 
7.9 
0.0025 
Eptatretus spp. (hagfishes) 
1.4 
0.9 
3.9 
1.8 
7.2 
2.3 
10.2 
3.5 
ns 1 
Raja spp. (skates) 
6.9 
2.8 
0.8 
0.8 
13.9 
2.0 
10.9 
5.6 
0.02 
Unidentified roundfish 
3.1 
2.1 
0.0 
nm 
19.2 
18.2 
6.1 
2.3 
nt 
Anoplopoma fimbria (sablefish) 
1.4 
1.5 
0.9 
0.9 
2.0 
1.3 
6.1 
2.9 
nt 
Hippoglossus stenolepis (Pacific halibut) 
0.0 
nm 
0.0 
nm 
2.7 
1.7 
0.0 
nm 
nt 
Microstomus pacificus (Dover sole) 
6.1 
6.0 
0.0 
nm 
9.4 
5.8 
3.1 
2.1 
nt 
Hydrolagus colliei (spotted ratfish) 
7.2 
3.0 
0.0 
nm 
62.1 
15.3 
0.7 
0.7 
nt 
Sebastes elongatus (greenstriped rockfish) 
1.3 
0.8 
0.0 
nm 
1.2 
1.2 
0.0 
nm 
nt 
Cottidae (sculpins) 
0.0 
nm 
1.6 
1.0 
0.0 
nm 
1.4 
1.4 
nt 
Agonidae (poachers) 
23.0 
4.1 
11.3 
3.2 
0.0 
nm 
0.0 
nm 
nt 
Unidentified fish 
0.0 
nm 
0.0 
nm 
0.0 
nm 
2.0 
2.0 
nt 
1 Not normalized by Box-Cox transformation, but ns in both Wilcoxon tests. 
taxonomic groups identified in Table 2 were present at 
sites 1A and 2A, respectively, whereas only 13 of these 
groups were recorded for sites IB and 2B. 
Discussion 
The data presented here indicate that fishing with 
ocean shrimp trawls in the deepwater mud habitats 
near Nehalem Bank has reduced invertebrate diver- 
sity and negatively impacted the abundance of several 
common macroinvertebrate taxa, such as sea whips, sea 
cucumbers, flat mud stars, sea stars, and squat lobsters 
(Table 2). For sea cucumbers and squat lobsters, the 
negative effects on abundance are probably a result of 
both capture in ocean shrimp trawls and mortality from 
physical damage caused by trawl doors and groundlines. 
For the other taxa, the physical effects of trawl doors 
and groundlines are probably most important. The four 
Nehalem Bank sites studied here represent a small 
