Geoscience Reference
In-Depth Information
islands, Hertford and Ciboux, better known simply as the Bird Islands. They are home to some four hundred
great cormorants, or 70 percent of the known North American population, qualifying them as the largest breed-
ing colony in eastern North America.
All of the islands rimming Nova Scotia's Atlantic coast have been separated from the mainland only relat-
ively recently by rising sea level and are located close to the shore—with the exception of Sable Island, loc-
ated 300 kilometers (190 miles) from the mainland. The island is the emergent part of a 1,000-meter-deep
(3,280-foot) deposit of sand left behind as an outwash fan when the Wisconsinan glacier melted and sea level
rose. Its shallow submerged bars harvested more than five hundred ships in the Age of Sail, earning Sable the
epithet “Graveyard of the Atlantic.” The crescent-shaped island is also a place of maritime fecundity, notably
as the largest gray seal colony in the world, with an annual pup production estimated at between forty and fifty
thousand.
Two endemic species are of particular interest: the Ipswich sparrow and the Sable Island pony. First dis-
covered in the winter of 1868 on a dune at Ipswich, Massachusetts, most Ipswich sparrows (a subspecies of
Savannah sparrow) breed only on Sable Island. The other endemic species is the famous Sable Island “pony,”
though “horse” is more descriptive and accurate. Horses were first introduced to the island in 1753 by Andrew
le Mercier, pastor of the French Church in Boston, who attempted to establish a colony there. The number of
horses in the herd fluctuates significantly, between 150 to 400 animals. During the months leading up to
winter, the horses forage on the luxuriant marram grass, achieving maximum fat levels in December. The relat-
ively mild climate of Sable means that the animals do not normally succumb to hypothermia; however, when
unusually heavy snowfall covers their food supply, disaster often follows.
Offshore, the edge of the Scotian Shelf (part of the North American Continental Shelf) is an area of en-
hanced phytoplankton production, which seems to be associated with shelfbreak fronts. An oceanic front is
defined as a sharp boundary where currents or water masses with different properties, such as temperature or
salinity, collide. At the boundary, there is often increased turbulence, with downwelling of denser water masses
and upwelling of less dense water. Such shelfbreak front areas are ecologically important, as floating organ-
isms, such as jellyfish and zooplankton, collect there and attract swordfish, bluefin tuna, sea turtles, sharks,
and seabirds.
