Table 5.10. Effects of toothed scallop dredges on
sand 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 |
| 1,2 |
Black and
Parry 1994, 1999 |
Port Phillip Bay, SE Australia
(three sites) |
15 m |
Sand (7-30% silt-clay) |
Sediment
plume; maximum depth of disturbance 4-6 cm into bottom; cutterbar trims off
high regions of seafloor. |
Turbidity
returned to normal storm levels within 9 min. |
Experimental dredging for 2-4 days (two to four tows per
unit area) in three areas with no commercial dredging for 4 yrs. |
| 3,4 |
Currie and
Parry 1996, 1999b |
Port Phillip Bay, SE Australia
(St. Leonards site) |
15 m |
Fine/very fine sand |
Flattening
of low-relief biogenic mounds; depressions filled in; parallel tracks
produced by skids; S fewer species after 3 wks; most species 20-30% less
abundant 3.5 mo after dredging; S reduced abundance of 6 of 10 most common infaunal species within first
3.5 mo (S increase for one species); no effect on total number of
individuals; surface-dwelling organisms released into water column right
away, burrowing organisms as dredging continued; increased abundance of more
mobile, opportunistic species within first 3.5 mo. |
Mounds
reformed after 6 mo; tracks visible after 1 mo, but not after 6 mo; most
species recovered within 8 mo, but some had not after 14 mo. |
Experimental
dredging for 3 days (2 tows per unit of area) in an area with no commercial
dredging for 4 yr; recovery of infauna monitored at 5 intervals during 14 mo;
seafloor changes at 8 days and at 6 and 11 mo. |
| 4 |
Currie and
Parry 1999b |
Port Phillip Bay, SE Australia
(Dromana site) |
15 m |
Medium-fine sand |
Removal
of small, parallel sand ripples; S reductions in abundance of three of ten
most common infaunal species within 2 days. |
Ripples
reformed after 5 days following storm. |
Experimental
dredging for 2 consecutive days (2 tows per unit of area) in an area with no
commercial dredging for 4 yr; effects on infauna evaluated after 2 days,
seafloor changes after 5 days. |
| Port Phillip Bay, SE Australia
(Portarlington site) |
15 m |
Muddy sand with shell fragments |
Flattening
of biogenic mounds; S reductions in abundance of 2 of 10 most common infaunal
species within 1 day. |
Mounds
reformed 7 months after dredging, but were still smaller than in undredged
area. |
Experimental
dredging for 4 days (four tows per unit area) in an area (Portarlington) with
no commercial dredging for 4 yrs; effects on infauna evaluated after 1 day,
seafloor changes after 7 mo. |
| 5 |
Butcher et al. 1981 |
Jervis Bay, New South Wales, Australia |
>13 m |
Sand |
Sediment
plume up to 5 m off bottom, flattening of sand ridges. |
Sediment
plume settled out within 15 min. |
Diver
observations. |
| 6 |
Eleftheriou
and Robertson 1992 |
Firemore Bay, Loch Ewe, Scotland |
5 m |
Well-sorted sand |
Dredge
eliminated natural bottom features; teeth created 3-4 cm deep furrows; no
effect on sediment characteristics; damage or mortality of larger epifauna,
razor clams, and sand lance, attraction of predators; increase in some
species of small infaunal crustaceans; initial reduction in polychaetes
followed by increase; no effect on taxa adapted to dynamic environment (e.g., amphipods, bivalves). |
Grooves
and furrows no longer visible shortly after dredging, duration depended on
wave and current action. |
Evaluation
of incremental effects of dredging (25 tows in 1 wk) at a single site (no control). |
| 7 |
Thrush et al. 1995 |
Mercury Bay, New Zealand |
24 m |
Coarse sand |
Breaking
down of surface sediment features; grooves 2-3 cm deep created by teeth; S
declines in abundance of 6 of 13 most common taxa at unexploited site, and 4
of 13 most common taxa at exploited site; S reductions in total number of
individuals and taxa at both sites. |
General
recovery of macrobenthic abundance at previously exploited site after 3 mo,
but not at unexploited site. |
Experimental
dredging (5 parallel tows in 1 day) at
a previously exploited and an unexploited site with different benthic
communities; biological effects evaluated within 2 hr and 3 mo after
dredging. |