910 Inner Shelf
The Inner Shelf District comprises a large geographic area extending from the Northumberland strait to the Bay of Fundy. The District has been divided into the following Units:
Geology and Seabed Morphology
On the Atlantic Coast (Region 800), the Inner Shelf is part of the Atlantic Uplands, a geomorphic division of the Appalachian Region. Here the bottom slopes steadily offshore to a distance of about 25 km and has much of its glacial deposits removed by the sea level advance, leaving significant exposures of bedrock.
In the Bay of Fundy and eastern Gulf of Maine, the Inner Shelf falls in the Fundian Lowlands, a part of the Carboniferous-Triassic lowlands of the Appalachian Region. The bottom contours largely follow the coastline and reflect its origin as a former drainage system originating in the Minas Basin-Truro area.
In Sydney Bight the Inner Shelf is largely underlain by Carboniferous rocks of the Sydney Basin. The topography is relatively flat and slopes gradually out to sea, forming an Inner Shelf bank. Bedrock exposures occur throughout this area.
West of Cape Breton in the southeastern Gulf of St. Lawrence, Ordovician to Middle Carboniferous rocks of the Antigonish and Cape Breton highlands extend under St. Georges Bay to approximately 16 km offshore. The west and central parts of the Northumberland Strait are underlain by horizontal or gently folded Upper Carboniferous and Permian sedimentary rocks.
Temperature and salinity are important components of oceanic climate and influence biological productivity. In February, upper layer temperatures in some areas are at or near freezing, while temperatures on the South Shore of Nova Scotia and in the Bay of Fundy are considerably warmer. August temperatures are highest in Northumberland Strait and become cooler southwestwards from Cape Breton along the Atlantic Coast (Region 800). At the sea surface on the Scotian Shelf, temperature and salinity increase as one moves southeastwards from land.
Algal cover in the Northumberland Strait and the Inner Bay of Fundy tends to be less dense in exposed areas because of the abrasive action of ice. The intertidal zone is scraped clean of algae every year to a depth of several metres below low tide marks and results in the development of a "lawn" of short developing plants in the scraped areas. Ice also lifts off large patches of Eelgrass in some areas, creating many underwater "potholes" and bare areas.
Phytoplankton productivity is high as a result of oceanographic processes which enhance nutrient supply in the coastal zone. Algal "blooms" of dinoflagellates and diatoms occur at peak productive times of the year - the spring and early fall. Dense concentrations of dinoflagellates can create luminescent displays in coastal inlets and add a glow to the wake of passing ships, and they can also cause shellfish poisoning.
Many species of fish and invertebrates such as lobster live on the Inner Shelf because of its favourable temperatures and feeding conditions. The young of many fish species find food and protection in the algal beds and rocky surface features. Many fish species live in coastal waters and nearby freshwater environments during part of the year.
Migratory fish species such as herring and mackerel move seasonally into these areas; herring frequently spawn in shallows and on some offshore banks, attaching their eggs to the seabed. Large schools of adult Mackerel approach the Atlantic coast in late May and leave again in the fall, accompanied by young-of-the-year. Coastal populations of Sand Lance and Atlantic Silverside shoal in nearshore waters. Cod move inshore as the water warms in the summer. The shelter provided by algal beds, rocks, and boulders - and an ample food supply - provide ideal habitat for lobster. Large clam species, particularly the Ocean Quahog, occur in the sediments.
Seals and whales use the Inner Shelf as both a seasonal and year-round food source. Whales, including the Humpback and Northern Right, move into the area from more southerly areas to feed on summer populations of plankton and fish. Many North Atlantic whale species also move through Nova Scotia inshore and offshore waters en route to summering areas further to the north. The small Harbour Porpoise is characteristic of the coastal zone.
The Inner Shelf supports Harbour and Grey seals which feed on fish and invertebrates in the nearshore zone for at least part of the year. Grey Seals from most Atlantic coastal areas migrate to Sable Island, where they give birth in the spring.
The Inner Shelf is also home to a host of North Atlantic seabirds, many of which nest on shore and feed on the rich animal life just offshore; included are gulls, terns, cormorants, and Storm-petrels. Isolated colonies of seabirds such as Atlantic Puffin, Razorbill, Black-legged Kittiwake, and gannets also occur along the coasts.
In general, the seasonal range of average water temperatures is higher in the upper layers than in the deeper layers, and is higher off Cape Breton than off Yarmouth. This reflects the reduced stratification and increased tidal mixing off Yarmouth.