Stellwagen Bank Final EIS and Management Plan 



Pc^e 14 



sandy submerged feature measuring nearly twenty 

 miles in length, occurring in a southeast-to- 

 northwest direction between Cape Cod and Cape 

 Aim, Massachusetts. Generally counterclockwise 

 surface currents flow over the Bank, where waters 

 depths range from 65 feet to over 300 feet. Bank 

 waters are characterized by two distinct productivity 

 periods annually, when overturn and mixing of 

 coastal waters with nutrient-rich waters from deeper 

 strata produce a complex and rich system of 

 overlapping midwater and benthic habitats. 



This cyclic biological productivity supports a large 

 variety of commercially important fisheries, which 

 have in turn supported generations of fishermen. 

 The Bank's resources are also important feeding 

 and nursery grounds for an abundance of 

 endangered cetacean species; and provide habitat 

 for several additional marine mammal species and 

 associated coastal/pelagic seabirds. Because of its 

 proximity to land, Stellwagen Bank attracts an 

 increasing number of commercial, recreational and 

 scientific users and visitors. 



Several additional human activities occur over or 

 near the Sanctuary, including transit of commercial 

 vessels and ocean disposal of dredged materials. 



1. Environmental Conditions 



a. Geology 



Like Cape Cod and the islands of Martha's 

 Vineyard and Nantucket, Stellwagen Bank and other 

 submerged banks and ledges off the northeastern 

 U.S. coast were created by the advance and retreat 

 of glaciers. The southward advance of massive ice 

 sheets nearly 19,000 years ago was influenced by the 

 existing topography; and the ice was shaped into 

 huge lobes. Two of these lobes created the land 

 masses identified above. One ice lobe was formed 

 by what is now Cape Cod Bay; the other by the 

 present-day Great South Channel, located to the 

 southeast of Cape Cod. The advance of ice over 

 the continental land mass ground the land into 

 fragments and carried them along with the 

 movement of the ice. 



With general climatic warming between 18,000 

 and 15,000 years ago, the glaciers began to melt and 



retreat from their coverage. The ice lobes became 

 more pronounced, and retreated at differing rates, 

 depending on the depths of topographical 

 depressions within which they moved. During this 

 process enormous amounts of pulverized continental 

 land were released from the melting ice. These 

 land fragments, or "outwash" from the two ice lobes 

 formed much of the present Cape Cod peninsula. 



Retreat of the ice lobe formed by the Great 

 South Channel was sufficiently slow that much of 

 the land fragments it carried melted out and were 

 deposited on the sea floor. These materials formed 

 the submerged elevation now known as Stellwagen 

 Bank. The Bank originally was made up of sand, 

 gravel, silt, and "rock flour" (ultra-finely ground 

 rock); but over time, most of the finer-grained 

 materials have been carried away by currents and 

 deposited in basin areas on either side of the Bank 

 (Tucholke and Hollister, 1973; Hassol, 1987; and 

 CampbeU, 1987). 



The outer rim of the Gulf of Maine (including 

 Nantucket Shoals, Georges Bank, and the Nova 

 Scotian Shelf) is floored primarily with Scmd and 

 gravel. There is a general tendency for grain size to 

 increase from southwest to northeast along this 

 portion of the Continental Shelf. 



The Gulf of Maine basin contains mostly silty- 

 clay, or clayey-silt sediments. Banks and ridges 

 within the Gulf of Maine are floored with gravel 

 and boulders; gravel and sand are usual substrates 

 in nearshore areas. 



Clayey-silt also covers most of Stellwagen Basin 

 and Cape Cod Bay, to the west of Stellwagen Bank. 

 Small hillocks of coarser, till-like sediment are also 

 generally found in both areas, and these areas may 

 act as local sources of detritus, in addition to the 

 contiguous Stellwagen Bank, Jeffreys Ledge, Tillies 

 Bank, and the coastal shelf. 



Shallow banks and ledges in this general area are 

 veneered by sand and mixtures of gravel and sand. 

 Jeffreys Ledge, north of Stellwagen Bank, is 

 composed primarily of gravel or gravelly-sand, and 

 is flanked by a sandy apron to the southeast. 

 Stellwagen Bank is mainly sand or pebbly-sand, 

 flanked to the east by gravel or gravelly-sand. The 



