Introduction Georges Bank was once the premier East Coast fishing ground for groundfish and scallops. The decline of groundfish species due to overfishing contributed to the increasingly restrictive management of fish stocks and a need to identify and pro- tect essential fish habitat (EFH). Marine habitat geology is the study of the distribution of geologic materials that form the seabed, the geologic processes (such as sediment movement and deposition) that affect the seabed, and the interplay of geologic factors and species behavior that gives rise to biologi- cal habitats in general and to specific habitats deemed essential to the success of a particular species (EFH’s). Management Needs In response to the growing need to manage fish stocks and to protect seabed environments and habitats, there is an increasing demand to know (1) the distri- bution of geologic materials and processes that are the framework of habitats (fig. 1), (2) the location and character of EFH’s, (3) the impact of habitat disturbance by fishing gear, and (4) the processes and time periods required for the recovery of disturbed habitats. Large areas on and near Georges Bank have been closed to fishing since December 1994 to conserve groundfish stocks (fig. 2). Sea scallops had been depleted in these areas, but they have recovered locally since 1994. Parts of the closed areas recently have been opened for a limited time to allow scallop dredging, thus raising questions regarding the distur- bance of EFH’s and the bycatch of pro- tected groundfish species. USGS Research Results Geologists and biologists of the U.S. Geological Survey (USGS), the National Marine Fisheries Service (NMFS) and National Marine Sanctuaries System (NMSS) of the National Oceanic and Atmospheric Administration (NOAA), the University of Rhode Island, and the Uni- versity of Connecticut have been conduct- ing joint studies of the seabed geology and biological habitats of Georges Bank for several years. These studies have shown that— • Herring spawning sites are located on gravel bottom only where currents are strongest • Juvenile cod survive best on gravel habitat, especially where sponges, tube worms, and other attached species (known as epifauna) increase the complexity of the seabed (fig. 1A) • Attached species are not able to colo- nize gravel habitat that is buried occa- sionally by moving sand • Dredging and trawling on gravel habi- tat remove epifauna and decrease habitat complexity, but fishing gear apparently has less long-term impact on sand habitat, especially where sand is moved by bottom currents • Scallops prefer habitats of gravel and nonmoving sand (weak bottom currents) • Closure of large areas to fishing allowed depleted sea scallop popula- tions to increase markedly in 4–6 years • Some sand-dwelling flounder species possibly prefer moving sand (strong bottom currents), but others prefer nonmoving sand habitats These results are being used by the New England Fishery Management Coun- cil (NEFMC) and the NMFS in deciding where fishing may occur and where the seabed must be closed to fishing to protect fish stocks and habitats. Seabed Mapping The absence of maps showing the geology and habitat character of the sea- bed is the greatest single obstacle to the gathering of information required for the informed and successful management of the region’s seabed habitats. The USGS has used multibeam sonar technology to map part of Closed Area I in the Great South Channel region (figs. 2, 3). The habitat information provided by these multibeam sonar images of the seabed has been used by the NEFMC to make man- agement decisions that opened some parts of Closed Area I to scallop dredging and protected other parts that are valued as groundfish habitat. U.S. Department of the Interior U.S. Geological Survey USGS Fact Sheet FS–061–01 July 2001 Habitat Geology Studies on and near Georges Bank, off New England Figure 1. Photographs of the seabed showing some typical Georges Bank habitats. See fig- ure 2 for locations. A, Undisturbed gravel habitat with epifauna of tube worms and other attached species. B, Gravel habitat disturbed by scallop dredges and lacking epifauna. C, Moving sand habitat (strong bottom currents) with sand dollars in ripple troughs. D, Non- moving sand habitat (weak currents) with sea scallops.
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IntroductionGeorges Bank was once the premier
East Coast fishing ground for groundfishand scallops. The decline of groundfishspecies due to overfishing contributed tothe increasingly restrictive management offish stocks and a need to identify and pro-tect essential fish habitat (EFH).
Marine habitat geology is the studyof the distribution of geologic materialsthat form the seabed, the geologicprocesses (such as sediment movementand deposition) that affect the seabed, andthe interplay of geologic factors andspecies behavior that gives rise to biologi-cal habitats in general and to specifichabitats deemed essential to the successof a particular species (EFH’s).
Management NeedsIn response to the growing need to
manage fish stocks and to protect seabedenvironments and habitats, there is anincreasing demand to know (1) the distri-bution of geologic materials and processesthat are the framework of habitats (fig. 1),(2) the location and character of EFH’s,(3) the impact of habitat disturbance byfishing gear, and (4) the processes andtime periods required for the recovery ofdisturbed habitats.
Large areas on and near GeorgesBank have been closed to fishing sinceDecember 1994 to conserve groundfishstocks (fig. 2). Sea scallops had beendepleted in these areas, but they haverecovered locally since 1994. Parts of theclosed areas recently have been opened fora limited time to allow scallop dredging,thus raising questions regarding the distur-bance of EFH’s and the bycatch of pro-tected groundfish species.
USGS Research ResultsGeologists and biologists of the U.S.
Geological Survey (USGS), the NationalMarine Fisheries Service (NMFS) andNational Marine Sanctuaries System(NMSS) of the National Oceanic andAtmospheric Administration (NOAA), theUniversity of Rhode Island, and the Uni-versity of Connecticut have been conduct-ing joint studies of the seabed geology
and biological habitats of Georges Bankfor several years. These studies haveshown that—• Herring spawning sites are located on
gravel bottom only where currents arestrongest
• Juvenile cod survive best on gravelhabitat, especially where sponges,tube worms, and other attachedspecies (known as epifauna) increasethe complexity of the seabed (fig. 1A)
• Attached species are not able to colo-nize gravel habitat that is buried occa-sionally by moving sand
• Dredging and trawling on gravel habi-tat remove epifauna and decreasehabitat complexity, but fishing gearapparently has less long-term impacton sand habitat, especially where sandis moved by bottom currents
• Scallops prefer habitats of gravel andnonmoving sand (weak bottom currents)
• Closure of large areas to fishingallowed depleted sea scallop popula-tions to increase markedly in 4–6 years
• Some sand-dwelling flounder speciespossibly prefer moving sand (strongbottom currents), but others prefernonmoving sand habitats
These results are being used by theNew England Fishery Management Coun-cil (NEFMC) and the NMFS in decidingwhere fishing may occur and where theseabed must be closed to fishing to protectfish stocks and habitats.
Seabed MappingThe absence of maps showing the
geology and habitat character of the sea-bed is the greatest single obstacle to thegathering of information required for theinformed and successful management ofthe region’s seabed habitats. The USGShas used multibeam sonar technology tomap part of Closed Area I in the GreatSouth Channel region (figs. 2, 3). Thehabitat information provided by thesemultibeam sonar images of the seabed hasbeen used by the NEFMC to make man-agement decisions that opened some partsof Closed Area I to scallop dredging andprotected other parts that are valued asgroundfish habitat.
U.S. Department of the InteriorU.S. Geological Survey
USGS Fact Sheet FS–061–01July 2001
Habitat Geology Studies on and near Georges Bank, off New England
Figure 1. Photographs of the seabed showingsome typical Georges Bank habitats. See fig-ure 2 for locations. A, Undisturbed gravelhabitat with epifauna of tube worms and otherattached species. B, Gravel habitat disturbedby scallop dredges and lacking epifauna.C, Moving sand habitat (strong bottom currents)with sand dollars in ripple troughs. D, Non-moving sand habitat (weak currents) with seascallops.
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Figure 2. Map of Georges Bank and nearby regions showing areasclosed to fishing since December 1994 (CAI, CAII, NLSCA), parts ofclosed areas that were opened seasonally to scallop dredging (pink),part of Great South Channel mapped by USGS multibeam sonar (orange;see fig. 3), gravel habitat on the northern edge of the bank (red outlines),
Figure 3. Part of Great South Channel (fig. 2) showing backscatterintensity draped over shaded-relief imagery of the seabed. Colorsof backscatter data derived from multibeam sonar mapping indi-cate the wide variety of habitats in this important fishing ground:orange indicates high-backscatter material (coarse sand andgravel); green indicates moderate-backscatter material (sand);and blue indicates low-backscatter material (fine sand). ClosedArea I (CAI) boundary is white dashed line. Area shown is 26 x 26kilometers.
a habitat area of particular concern (HAPC, yellow) recognized for juve-nile cod, boundary (green line, dashed where inferred) between movingsand habitat (strong bottom currents) and nonmoving sand habitat(weak currents), and locations of habitats shown in figure 1 (A, B, C,and D). Base map from NOAA’s National Ocean Survey Chart 13200.
For more information, please contact:
Page C. ValentineU.S. Geological Survey384 Woods Hole RoadWoods Hole, MA 02543–1598Telephone: (508) 457–2239E-mail: [email protected]
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Habitat Geology Studies on and near Georges Bank, off New EnglandIntroductionManagement NeedsUSGS Research ResultsSeabed MappingFor more information
FIGURESFigure 1. Photographs of the seabed showing some typical Georges Bank habitatsFigure 2. Map of Georges Bank and nearby regionsFigure 3. Part of Great South Channel (fig. 2) showing backscatter intensity draped over shaded-relief imagery of the seabed.
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