More than 10 species of sharks are found in the Derwent estuary. Common species inhabiting inundated tidal flats are the school shark Galeohinus galeus and gummy shark Mustelus antarcticus. These two species are small sized sharks that look fairly similar. Their long sleek bodies enable them to pursue and catch fish and squid, which are their favoured prey. Inshore areas are particularly important as birthing and nursery sites. The shallow protected waters of estuaries and coastal bays provide habitat for juveniles to feed and grow. Then they venture out into deeper waters as adults, and are known to make long migrations (up to 1400 km) that appear to be associated with reproduction. Ralphs Bay is especially important for gummy and school shark of one to two years in age. Large numbers of school shark pups were recorded during the 1940s and 50s, but recruitment has declined in the Derwent estuary. The Derwent estuary and neighbouring areas have been formally recognised as Shark Refuge Areas to protect sharks. Fishing is restricted in these sheltered habitats so sharks, skates and rays can breed and raise their young. No shark, skate or ray of any kind may be taken in Shark Refuge Areas. If caught in nets or on a rod and line they must be returned to the water as soon as possible with a minimum of damage. Juvenile draught board and seven-gilled sharks may also use the Ralphs Bay as a pupping ground.