Table
5.12. Effects of toothed scallop dredges on mixed substrate habitat: summary
of published studies. (S = statistically significant; citations
in bold print are peer-reviewed publications.)
| No. |
Reference |
Location |
Depth |
Sediment |
Effects |
Recovery |
Approach |
| 1 |
Bradshaw et al. 2002 |
Isle of Man, Irish Sea |
Not given |
Sand and gravel |
More
vulnerable taxa less abundant in recent samples, less vulnerable taxa more
abundant; faunal differences and proportion of species “lost” between time
periods increased significantly as number of years since fishing began
increased; no effect of increases in total effort; no clear evidence over all
sites for reduced species diversity. |
|
Recent
benthic sample data collected at 7 sites exposed to varying amounts of
fishing effort compared with data collected 50-60 yr ago, when scallop
fishing was very limited. |
| 2,3 |
Bradshaw et al. 2000, 2001 |
Isle of Man, Irish Sea |
25-40 m |
Gravel, sand, and mud |
6
mo of experimental dredging in closed area altered community structure, no
trends in abundance of individual species; no S effects on number of species,
but community heterogeneity was reduced; encrusting species were more
abundant and upright species less abundant in dredged plots than in control
plots after 3 yr. |
S
increases in abundance of several epifaunal species in undredged portion of
closed area 5-9 yr after closure. |
Continuous
experimental dredging (10 tows every 2 mo for 3 yr) in an area closed to
commercial fishing for 6 yr; semi-annual grab sampling inside and outside
closed area, and biannual diver surveys of epibenthic animals in closed area. |
| 4 |
Caddy 1973 |
Chaleur Bay, Gulf
of St. Lawrence, Canada |
40-50 m |
Gravel over sand, with occasional cobble and
boulders. |
Shallow,
flat tracks; tooth marks in sand; boulders dislodged and small rocks “plowed”
by dredge; spoil ridges at edges of track. |
|
Submersible
observations and photographs of tow tracks made <1 hr after dredging. |
| 5 |
DFO 1993 |
Bras d’Or Lakes, Nova Scotia, Canada |
10-500 m |
Gravel and mud |
Furrows
left by dredge teeth; berms at outer edges of dredge track. |
|
Sidescan
sonar survey 1 yr after area was closed to mobile gear. |
| 6 |
Kaiser,
Hill et al. 1996 |
Irish Sea, southwest of Isle of
Man |
Not given |
Not given, assume mixed substrates |
Reduced
abundance of most large epibenthic species; same effects on community
structure as beam trawls, but lower bycatch. |
|
Experimental
study of effects of dredging (10 tows) and beam trawling on large epifauna;
sampling with small-mesh (40mm) beam trawl both before and 24 hr after
fishing. |
| 7 |
Kaiser,
Ramsay et al. 2000 |
Irish Sea |
Not given |
Coarse sand and gravel |
S
more epifaunal organisms in areas exposed to high fishing effort, no effects
on infauna or on diversity or number of epifaunal species; shift from
communities dominated by more larger-bodied to fewer smaller-bodied
organisms. |
|
Compared
benthic communities in areas exposed to 10 yr of low and high fishing effort. |
| 8 |
Veale et al. 2000 |
Irish Sea |
20-67 m |
Coarse sand or gravel, often overlain with pebbles,
cobbles and dead shell. |
S
decreases in epibenthic species diversity and total number of species and
individuals with increasing fishing effort; total abundance, biomass, and
production and production of most taxa S decreased with increasing effort. |
|
Compared
dredge bycatch from fishing grounds exposed to varying amounts of fishing
effort during previous 60 yr. |