The Tamar Estuary MCZs are located in two spatially separate areas. The MCZs cover an area of approximately 15 km2 and include the upper reaches of the Tamar and Lynher estuaries of South Devon and Cornwall.
The sheltered habitats found within this site are subject to various salinity levels and tidal exposures. This diverse estuarine environment supports a number of features of ecological importance. These MCZs are particularly important as they are the only site where smelt (Osmerus eperlanus) is protected. Smelt is a migratory fish species which has suffered large declines throughout its range and is known to breed in the Tamar.
https://www.gov.uk/government/publications/marine-conservation-zone-2013-designation-tamar-estuary
The MCZs protect a variety of habitats including intertidal biogenic reefs and coarse sediments. Biogenic reefs are made from the hard parts of animals, such as blue mussels, and are formed when the animals’ shells are bound together with mud and sand by the sticky byssus thread or ‘beards’ of the mussels. These living reefs are ecologically important as they provide a home or refuge for seaweeds and animals including barnacles, winkles and small crabs.
Smelt (Osmerus eperlanus) are shoaling fish, distantly related to the salmon. Smelt are silvery-green in colour and typically around 20 cm long, and unusually they have been recorded to smell like fresh cucumber. They live in the salty water of estuaries and go upriver to spawn in fresh water before returning to sea. They have been included as a protected species within the Tamar Estuary MCZs because of the importance of this area for their breeding. The smelt population is depleted and protecting estuaries used by the species is important because they can become locally extinct from isolated estuaries and will not return. The MCZs are also home to the Native oyster (Ostrea edulis), a species which experienced significant declines during the 20th century in European waters.