Shellfish is a broad term used to describe crustaceans and molluscs. Shellfish play an important role in estuarine food webs.
They are also important in recreational and commercial fishing.
Under the Fisheries Management Act 1994 and the Fisheries Management (General) Regulation 2010, the definition of fish includes shellfish and other invertebrates such as worms, sponges, corals, aquatic insects and sea urchins, and sharks and rays.
The responsibility for threatened species and their management is shared between NSW Department of Primary Industries and the Department of Planning, Industry and Environment – Environment, Energy and Science under the Biodiversity Conservation Act 2016.
Prawns are a main source of food for fish that live in estuaries.
Prawns also form a significant component of the commercial fishing industry and are a favoured species in recreational fishing. In New South Wales, the main species of prawn that rely on New South Wales estuaries to complete their lifecycle are the school prawn, eastern king prawn and greasyback prawn.
Crabs live in the mud and sandflats in estuaries, in mangroves and on rocky break walls. Crabs commonly found in NSW estuaries include semaphore, mud, soldier, blue swimmer and hermit crabs.
Most crabs need saltwater to survive, which limits their distribution upstream.
Oysters, cockles and mussels
Oysters, cockles and mussels are bivalve filter feeders and help maintain water quality in estuaries. They are not very mobile – some settle on surfaces and remain there for most of their lives and others partially bury in soft sediment and only move with large waves and strong currents.
Oysters grow in large clusters and form complex reefs which provide habitat for many other estuarine species while filtering the water that passes over them. Global efforts are being made to create, maintain and protect oyster reefs due to their ecological value. These shellfish form a large part of the commercial fishing industry in NSW.
There are 3 types of oysters in NSW:
- the endemic Sydney rock oysters, which are commercially cultivated in sheltered estuaries such as Wallis Lake and the Clyde River
- the introduced Pacific oysters, which are found in the Hastings River and all estuaries to the south
- the native flat oyster, which occurs in sheltered waters of the south coast.
For more information see the oysters webpage on the NSW Department of Primary Industries website.
Cockles are efficient filter feeders, filtering up to 1.5 litres of water per hour! Like many other filter feeders, cockles can retain contaminants dissolved in the water as they feed.
Two types of cockles are found in NSW estuaries:
- the Sydney cockle, which lives in seagrass beds and mud flats
- the sand cockle, which is found in tidal flats and seagrass beds in estuary mouths.
Mussels grow in large clusters on hard natural surfaces or artificial structures like pylons and jetties. They often occur in clumps in shallow margins around estuaries after wind, waves or boat wash causes them to come loose from where they were attached.
Two main species of mussel live in NSW estuaries:
- the blue mussel, which often attaches to rocks and structures such as pylons and mooring floats at the seaward end of an estuary
- the pygmy mussel, which is found in high numbers on rocks and mangrove roots in the upper parts of estuaries.
Eight species of freshwater mussels live in coastal streams in NSW.