The heart of the sanctuary is Stellwagen Bank, an underwater plateau stretching 19 miles (17 nmi; 31 km) north to south, and 6 miles (5.2 nmi; 9.7 km) across at its widest near its southern end. The bank is, on average, 100 to 120 feet (30 to 37 m) below the surface, while surrounding waters to the west are over 300 feet (91 m) deep and to the northeast as deep as 600 feet (180 m).
The underwater cliff-edge of Stellwagen Bank runs parallel to the coastline and is referred to as the "shelf break." The shelf break is a steep slope which descends thousands of feet (hundreds or thousands of meters) to the ocean floor. Deep nutrient-rich ocean currents flowing along the coastlinee are forced upwards toward the surface when they come into contact with the steep slopes of the bank’s plateau. This creates upwelling at the shelf break, which occur because there are ocean currents flowing along the coast, slower moving water at the bottom of the ocean due to friction, stratified water separated by density, salinity, and temperature, and a dramatic change in seafloor slope.[1] This upwelling brings nutrients to the surface for phytoplankton, which attracts larger organisms to feed.
Stellwagen Bank owes much of its existence to the last major ice age. The Laurentide Ice Sheet advanced over the eastern United States 25,000 years ago, pushing in front of it large amounts of earth and rock. The southern margin of the glaciers formed local geographical features including Cape Cod and Stellwagen Bank. Originally, the Stellwagen Bank was above water, but gradually subsided over time as the post-glacial rebound subsided.
In the 17th century it was observed that the area made for excellent fishing. Large cod and tuna were caught frequently in the area, and whaling ships caught many whales in the area.
In 1854, the United States Navy sent Lieutenant CommanderHenry Stellwagen to survey and map the area. It was known that there was an ocean bank in the area, but its extent and shape were not known. Sounding could show ships how close they were to the dangerous waters of Boston Harbor, and so better maps were needed. Prior to Stellwagen's hydrographic survey, it was believed there were two small banks in the area, one just to the north of Cape Cod, and one in the middle of the entrance to Massachusetts Bay. Stellwagen showed that they were part of one large bank. As a result, the U.S. Navy named the bank after him in 1855.
In 1999, the submersibleDeepWorker 2000 was used to quantify the species of fish as well as the space resources within the sanctuary.[6]Remotely operated underwater vehicles were used from 1993 to 2003 to make additional observations of the fish within the sanctuary and adjacent waters.[6]
