Nature and science

Location & Geography

Perched on the edge of the Continental Shelf clings a crescent shaped isle alone in the North Atlantic. This is Sable Island, Nova Scotia; a vegetated sand bar approximately 290 km from Halifax, at 44˚N 60˚W. Roughly 42 km in length, and no more than 1.3 km at its widest, it spans a total area of 3,400 ha, approximately seven times the size of McNabs Island in the Halifax Harbour.

The island is flanked on the north and south by two long parallel beaches separated by a mature dune system. The interior topography is characterized by low rolling dunes with a number of freshwater ponds, especially in the west. Both the eastern and western tips are 2-6 km long flat expanses of sand known as the East and West Spits. In the centre of the island, and running for approximately two thirds of the total length of the island, is a series of high dunes which is one of Eastern Canada's largest dune systems.

A freshwater lens, maintained by precipitation, underlies Sable Island and surface exposures of this lens form the island’s freshwater ponds. The freshwater lens floats on top of the salt water due to the difference in specific gravity. The ponds provide habitat for unique plant and animal communities and fresh water for the island’s inhabitants. Potential saltwater contamination of the ponds is considered a major threat, particularly if dunes erode or if the rate of consumption becomes greater than the ponds’ capacity to recharge. Lake Wallace, a very shallow brackish-water lake in the centre of the island to the south, is about one kilometre in length, but was once much larger, having mostly been filled in by blowing sand.

The climate of Sable Island is temperate; however, during winter months, the moderating influence of the Gulf Stream results in some of the warmest temperatures in Canada. Given its remote position in the Northwest Atlantic, the island is often exposed to very strong winds. There are frequent heavy fogs in the area: on average there are 127 days out of the year that have at least one hour of fog.


Flora & Fauna

Sable Island's unique topography and dune system owe their existence to the sand-anchoring properties of vegetation. Approximately 1/3 of the island is vegetated1 and most of the native flora of Sable Island is typical to similar dune environments in Eastern North America. The island’s interior is largely dominated by heath-type vegetation, while the extremities are vegetated mainly by salt-tolerant and sand-loving plants, such as sandwort and marram grass. Over 190 plant species have been identified on Sable and 20 of them are considered to have a restricted distribution elsewhere2.

Since the 16th century, many domestic animals, including horses, cattle, goats, and rabbits, have been released on the island. The ecology of the island prior to such introductions is largely unknown. Currently, the only introduced mammal on the island is the feral horse. The horses are believed to have been introduced sometime shortly after 1738. Their numbers have ranged between 150 and 400 individuals, with current estimates placing them at a minimum of 375 animals3. They are dependent upon the island's vegetation for their nutrition, but supplement their diet with kelp and seaweed that wash up on the beach.

The island was once home to a breeding population of the Atlantic Walrus (listed as Extirpated under the Species at Risk Act). They were hunted heavily for their ivory and were last seen on the island in the late 1800s. Today evidence of walrus on the island can be found when shifting sands reveal remaining walrus tusks, having been buried for possibly hundreds of years.

Sable Island is home to the world’s largest breeding colony of grey seals, which pup between late December and early February. The population has experienced significant growth in recent decades, but the rate of growth has slowed more recently4. During the breeding season, grey seals occupy the beaches and both vegetated and non-vegetated inland habitats throughout the island. For the remainder of the year, grey seals generally haul out on the beaches in groups of dozens to thousands of individuals, with a particularly large number on the island during the annual moult in May and June. There is also a small resident population of harbour seals which pup from mid-May to mid-June. This population has decreased in recent years, with shark predation and competition from grey seals suggested as reasons for the decline5. Other visitors include ringed, harp and hooded seals; however they do not breed on the island.

Sable Island is part of a key migratory flyway, with numerous bird species (over 350) recorded. These include species similar to those found on the mainland, but also a high number of vagrants that are far from their normal habitats. Sixteen bird species have been confirmed to breed on the island during the spring and summer months. The best-known bird associated with the island is the Ipswich Sparrow, a subspecies of the Savannah Sparrow, which breeds only on Sable Island. The island also has a significant gull population that can be found there year-round. Both the Ipswich Sparrow and Roseate Tern are classified as Special Concern and Endangered, respectively, under the Species at Risk Act. Critical habitat for Roseate Terns has been identified in several locations and must be protected from disturbance during the breeding season.

The freshwater ponds on the island (primarily in the area between Main Station and BIO House) support a number of fish species, including mummichogs, sticklebacks and American eel. Sable is home to at least six invertebrate species found only on the island; in particular, there are several species of butterflies and moths that may be sufficiently different from mainland populations that they could be classified as subspecies6. Noteworthy among the stray species which have been sighted on Sable are two tropical species of moth/butterfly, recorded for the first time in Nova Scotia.

The unique assemblage of the flora and fauna of Sable Island combined with its unusual topography results in a fascinating narrative of geographical and ecological dynamics.

 

  1. Freedman, B. 1996. Airphoto assessment of changes in plant cover on Sable Island, Nova Scotia. Unpublished report, Canadian Wildlife Service. (return to source)

  2. Catling, P.M., Freedman, B. & Lucas, Z. 1984. The vegetation and phytogeography of Sable Island, Nova Scotia. Proceedings of the Nova Scotian Institute of Science 34: 181-245. (return to source)

  3. Lucas, Z.L., McLoughlin, P.D., Coltman, D.W., & Barber, C. 2009 Multiscale analysis reveals restricted gene flow and a linear gradient in heterozygosity for an island population of feral horses. Canadian Journal of Zoology, 87: 310-316. (return to source)

  4. DFO. 2009. Science Advice on Harvesting of Northwest Atlantic grey seals (Halichoerus grypus) in 2009. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2008/061. (return to source)

  5. Bowen, W.D., Ellis, S.L., Iverson, S.J., and Boness, D.J. 2003. Maternal and newborn life-history traits during periods of contrasting population trends: implications for explaining the decline of harbour seals (Phoca vitulina), on Sable Island. J. Zool. Lond. 261:155-163. (return to source)

  6. Wright, B. 1989. "The Fauna of Sable Island." Nova Scotia Museum Curatorial Report Number 68. (return to source)