Fish in the Avoca–Avonmore Catchment

Lakes in Avoca Avonmore Catchment

The rivers, lakes, and estuary of the Avoca–Avonmore catchment support a range of fish species that reflect the natural conditions of the area’s waters. Six fish species live in the freshwater parts of the catchment: brown trout, Atlantic salmon, eel, minnow, brook lamprey, and river lamprey. Sea trout, a migratory form of brown trout, also occur.

A 2008 survey recorded eleven fish species in the Avoca Estuary, including salmon, brown trout and sea trout, eel, river lamprey, three-spined stickleback, sprat, sand goby, five-bearded rockling, whiting, flounder, and thick-lipped grey mullet. The first four are migratory fish, while the others are typically found in estuaries. An estuarine form of brown trout called slob trout may also occur.

Brown trout are the most common fish in the rivers and lakes of the catchment. They are found from the upper tributaries at about 400 metres down to the estuary, though they are generally small and at low population densities. Surveys have found that most trout are one-year-old, with slow growth due to the low nutrient levels in the rivers, which limit the availability of food. In the more fertile Aughrim River, trout grow faster and larger.

Trout feed mainly on aquatic invertebrates such as caddis and mayfly larvae, but also eat insects that fall from riverside vegetation. Where food is scarce, some brown trout migrate to the sea to feed and return to spawn. These are known as sea trout or white trout. Most sea trout are female and may spawn several times.

Sea trout. Photo courtesy of Chris McCully and Ken Whelan – Nomads of the Tides

Their young spend one to three years in the rivers before migrating to sea, returning later to spawn again.

The Avoca–Avonmore system was once famous for its large runs of Atlantic salmon before mining began in the 18th century. Pollution from the mines greatly reduced their numbers, though some salmon continued to reach spawning grounds in the upper rivers. Juvenile salmon have been recorded in several surveys, but their numbers remain low. The catchment has the potential to support many more salmon if pollution is reduced and migration routes improved.

Other fish found in the catchment include the native three-spined stickleback and the non-native minnow, both small species common in the rivers, lakes, and the estuary.