Table
5.4. Effects of otter trawls on mud 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 |
Ball et al. 2000 |
Irish Sea |
75 m |
Sandy silt |
Reduced
infaunal and epifaunal richness, diversity, number of species, and
individuals in fishing ground compared to wreck site, but no obvious effects
on macrofauna 24 hr after trawling. |
|
Experimental trawling in
heavily fished prawn fishing ground, unfished area near a shipwreck used as
control. |
| 2 |
Brylinsky et al. 1994 |
Bay of Fundy, Nova Scotia, Canada |
Intertidal |
Silt and coarse sand overlain with silt |
Door
tracks in sediment, rollers compressed sediment; S decrease in nematodes and
benthic diatoms in door tracks, no effects on larger infaunal organisms
(mostly polychaetes). |
Furrows
visible 2-7 mo; nematodes recovered in 1-1.5 mo, diatoms in about 1-3 mo. |
Four trawling experiments
(repeated tows during a single day) at two locations in a trawled area,
effects evaluated for 1.5-4 mo. |
| 3 |
DeAlteris et
al. 1999 |
Narragansett Bay, Rhode Island, USA |
14 m |
Mud |
Doors
produced tracks 5-10 cm deep and adjacent berm 10-20 cm high. |
No
changes in hand dug trenches for >60 days. |
Diver observations. |
| 4 |
Drabsch et al. 2001 |
Gulf of St. Vincent, South Australia |
20 m |
Fine silt |
Trawl
door tracks, smoothing of topographic features; S decrease in total infaunal
abundance and one group of polychaetes, damaged epifauna. |
|
Experimental
trawling (two tows per unit of area in 1 day) in area with no trawling for 15
yrs (one site); effects evaluated after 1 wk. |
| 5 |
Frid et al. 1999 |
Northeast England (North Sea) |
80 m |
Silt-clay |
S
increase in total number of individuals in taxa predicted to increase at high
fishing effort and number of errant polychaetes; no effect of increasing
effort on total number of individuals expected to decrease, but S decline in
sea urchins. |
|
Related
changes in benthic fauna in a heavily trawled location to low, high, and
moderate fishing activity and to changes in phytoplankton production over 27
yr. |
| 6 |
Hansson et al. 2000 |
Fjord on the west coast of Sweden |
75-90 m |
Clay |
Abundance
of 61% infaunal species negatively affected and S reductions in abundance of
brittle stars during last 5 mo of disturbance period; S reductions in total
biomass at 3 of 3 trawled sites and 1 of 3 control sites, and in number of
individuals at 2 of 3 trawled sites and 1 of 3 control sites; abundance of
polychaetes, amphipods, and mollusks not affected. |
|
Experimental trawling for 1 yr (two tows per wk, twenty-four tows per
unit of area) in area closed to fishing for 6 yr (three treatment and three
control sites); effects evaluated during last 5 mo of experiment. |
| 7 |
Mayer et al. 1991 |
Maine
coast, USA |
20 m |
Mud |
Dispersal
of fine surface sediment; doors made furrows several cm deep; some planing of
surface features, but no plowing of bottom or burial of surface sediments. |
|
Experimental
trawling (single tow); examined immediate effects on sediment composition and
food value to sediment depth of 18 cm. |
| 8 |
Pilskaln et al. 1998 |
Gulf of Maine, USA |
250 m |
Mud |
Greater
abundance of suspended infaunal polychaetes in more heavily trawled area. |
|
Deployed
sediment traps in fishing grounds 25-35 m above substrate. |
9 |
Sanchez et al. 2000 |
Coast of Spain,
Mediterranean Sea |
30-40 m |
Mud |
Door
tracks in sediment; no change in number of infaunal individuals or taxa, or
in abundance of individual taxa; no changes in community structure. |
Door
tracks still clearly visible after 150 hr. |
Experimental
trawling in trawled area at two sites swept once and twice in a single day;
effects evaluated after 24, 72, 102, and 150 hr. |
| 10 |
Sparks-McConkey
and Watling 2001 |
Penobscot Bay, Maine, USA |
60 m |
Mud |
S
decline in porosity, increased food value, and increased chlorophyll
production of surface sediments; S reductions in number of infaunal
individuals and species, species diversity, and abundances of 6 polychaete
and bivalve species, S increase in nemerteans. |
All
geochemical sediment properties and all but one polychaete/bivalve species
recovered within 3.5 mo, nemerteans still more abundant after 5 mo. |
Experimental
trawling (four tows in 1 day) in untrawled area; pre-trawl sampling of
sediments and infauna for a year; recovery monitored for 5 mo. |
| 11 |
Tuck et al. 1998 |
West coast of Scotland |
30-35 m |
Fine silt |
Tracks
in sediment, increased bottom roughness; no effect on sediment
characteristics; S increase in number of infaunal species at end of 16 mo
disturbance period and during 18 mo recovery period; no change in biomass or
number of individuals at end of recovery period; S increase in polychaetes, S
decrease in bivalves; mixed results of analyses of community structure, S
reduction in diversity during first 22 mo. |
Door
tracks still evident after 18 mo; bottom roughness recovered after 6 mo;
nearly complete recovery of infaunal community within 12 mo, complete after
18 mo. |
Experimental
trawling for 1 day/mo (one and a half tows per unit of area) for 16 mo in
area closed to fishing for >25 years; recovery monitored after 6, 12, and
18 mo. |