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Ecosystem/Bras d'Or Lake
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Sounding Out Sinkholes
Using a sophisticated multi-beam sonar system, researchers from the Geological Survey of Canada have discovered that the floor of the Bras d’Or Lakes is peppered with a number of large circular depressions, or sinkholes. The holes, some up to 150 metres deep, are thought to correspond to gypsum deposits, and are similar to those found on nearby land. The sonar survey of the Lakes is also revealing that as recently as 7,000 – 8,000 years ago, the inland sea was a series of small freshwater lakes, connected by meandering rivers. The discovery of ancient beaches, shorelines and spits suggests that many secrets of ancient First Nations cultures lie under the waters of the Bras d’Or Lakes.

Bras d’Or Biology

Oysters thrive, but rock crabs and sea scallops struggle. Ocean species such as mackerel, winter flounder and Greenland cod dominate the finfish population, along with a population of introduced rainbow trout. Crustaceans such as sand shrimp co-exist with marine invertebrates such as jellyfish, sea urchins and starfish. Seaweeds typical of the Gulf of St. Lawrence grow in deeper waters, while a combination of saltwater and freshwater marsh plants line sheltered bays.

The brackish waters of the Bras d’Or Lakes support an aquatic ecosystem that blurs the boundary between freshwater and saltwater species. Estuarine plants and animals dominate, and those that can survive conditions of low to moderate salinity do best. Recent trawling surveys show that winter flounder and cod are the most common finfish species in the Bras d’Or. Black-spotted stickleback are also numerous, and recent scientific research suggests that a genetically distinct, spring-spawning population of blueback herring may remain in the inland waters throughout the year. (Recent studies have shown a marked decline in the number of herring larvae in the Lakes and a reduced number of herring spawning beds; this led to the closure of the herring fishery in 1999. Commercial trawling for winter flounder was banned in 1992.)

While lobsters thrive in some areas of the Bras d’Or, supporting an ongoing food fishery, the salinity level of the Lakes is generally too low to support their larval development. It is far more suitable for the growth and cultivation of American oysters, a hardy species that can thrive in a wide range of temperatures and varying levels of salinity. This bivalve, however, is currently under assault from fecal coliform pollution, the deadly MSX parasite and potentially, the bio-invading European green crab.
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