Introduction

Maquoit Bay, which forms the

northwestern arm of Casco

Bay, Maine (fig. 1), has an extensive eelgrass meadow of over 1,300 acres covering half the bay bottom. When eelgrass

began piling up on the shoreline early in

the summer of 1999, local residents

knew something was wrong. Preliminary

evidence pointed to commercial mussel

dragging as the source of habitat disturbance — large bare areas within the eelgrass meadow were marked with distinctive, linear dredge scars on the bay bottom, and piles of mussel shell appeared

to have been dumped overboard during

mussel washing and sorting operations.

Although natural resource managers,

shoreline citizens, commercial harvesters,

and scientists had all expressed concern

over the years about the impacts of commercial mussel dragging on eelgrass habitat throughout Maine, no scientific study

had ever measured the magnitude of

damage from dragging. Significant damage to eelgrass beds by mussel dragging

could have negative effects on the fishery, as eelgrass is known as important

habitat for blue mussel larvae.

Therefore, the U.S.

Geological Survey (USGS) provided funds from its State

Partnership Program, which is

focused on state natural

resource management problems, to address issues concerning commercial mussel

dragging in Maine eelgrass

beds. In 2000, scientists from

the USGS, the University of

New Hampshire, and the

Maine Department of Marine

Resources embarked on a

study to quantify the effects of

mussel dragging on eelgrass in

Maquoit Bay and to project the

time required for the habitat to

recover from dragging impacts. 

Impact of Dragging on Eelgrass

Commercial dragging for mussels

occurred in Maquoit Bay throughout the

1990s, leaving four identifiable dragging

scars ranging from 8 to 79 acres in size.

The largest of these scars is shown in figure 2. Aerial photographs of Maquoit

Bay taken in 2000 revealed that a total of

132 acres of eelgrass, or about 10 percent of the eelgrass in the bay, had been

disturbed by dragging. Two sites that

U.S. Department of the Interior

U.S. Geological Survey

For more information, contact: 

Director, Patuxent Wildlife Research Center (PWRC)

12100 Beech Forest Road, Laurel, Maryland 20708

(301) 497-5500 http://www.pwrc.usgs.gov

PWRC Fact Sheet FS 2005-3054

June 2005
were dragged in 1999 had very little eelgrass cover in 2000. Dragging completely uprooted eelgrass plants, removing

leaves, rhizomes, and roots. Underwater

video measurements showed that dragging intensity was variable. In some

areas, patches of mature plants remaining after dragging suggested relatively

light impacts; however, an average of 86

percent of the recently dragged bottom

was bare, indicating heavy dragging over

most of the area. Two older dragging

scars (one that had been dragged 2 to 7

years earlier and one that had been

dragged more than 8 years earlier)

showed continuous eelgrass cover in

2000, but drag marks were still evident

and eelgrass abundance was still substantially reduced. Dragging did not alter the

physical characteristics of the sediment.

Eelgrass Recovery Following

Dragging

The pattern and rate of eelgrass bed

recovery depended on initial dragging

intensity. Aerial photographs showed

patchy eelgrass regrowth in areas of relatively light dragging after 1 year, but very

little revegetation in heavily dragged

areas (fig. 3). 

Two independent methods were

used to predict the rate of eelgrass recovery in heavily dragged areas. One

method was based on measurements of

the current eelgrass abundance at sites

that were dragged at different times over

the past decade. The other method

involved development of a computer

model of eelgrass revegetation, based on

measurements of the rate of seedling

appearance and plant growth in dragged

areas. Both methods led to the same

prediction — it takes an average of 11

years for eelgrass in dragged areas to

revegetate to a level of 95 percent of the

eelgrass cover found in undisturbed

beds. It is important to note that the eelgrass meadow in Maquoit Bay was

expanding during this study, indicating

that conditions were highly favorable for

eelgrass growth. The computer model

predicted that under conditions less

favorable for eelgrass growth, such as

reduced water quality, recovery could

take up to 22 years. 

For More Information

Neckles, H.A., F.T. Short, S. Barker, and

B.S. Kopp. 2005. Disturbance of eelgrass Zostera marina by commercial

mussel Mytilus edulis harvesting in

Maine: dragging impacts and habitat

recovery. Marine Ecology Progress

Series 285:57-73.

Contacts

Hilary A. Neckles, USGS Patuxent Wildlife

Research Center, 196 Whitten Rd.,

Augusta, ME 04330, 207-622-8205 x

119, hilary_neckles@usgs.gov

Frederick T. Short, Jackson Estuarine

Laboratory, University of New

Hampshire, 85 Adams Pt. Rd.,

Durham, NH 03824, 603-862-5134,

fred.short@unh.edu

Seth Barker, Maine Department of Marine

Resources, PO Box 8, West Boothbay

Harbor, ME 04575, 207-633-9507,

seth.barker@maine.gov

Blaine S. Kopp, USGS Patuxent Wildlife

Research Center, 196 Whitten Rd.,

Augusta, ME 04330, 207-622-8201 x

114, bkopp@usgs.gov