The brown trout is very common in Ireland and is typically found in all of our rivers and lakes. Populations of brown trout can persist locally and do not need to migrate long distances as long as their habitat provides enough food and suitable locations for spawning, growth and refuge.
Sea trout, however, are different. Sea trout is the collective word for anadromous brown trout, a term that describes fish that live at sea but return to freshwater for spawning. Sea trout born in rivers are indistinguishable from brown trout as young fish, but as they get older, sea trout turn silver, move downstream and enter the sea or the estuary to feed. At sea, they grow quickly, feeding on abundant supplies of food. Sea trout are migratory, returning from the sea to spawn in rivers and back again to the sea to feed. This means that barriers in rivers, such as dams or weirs, can impede their access to spawning habitat, and sea lice infections can be a problem for sea trout that migrate through areas with aquaculture.
The aim of this project is to examine sea trout stocks and the potential impact of salmonid aquaculture on their growth rates at sea. To do this, we will use a mixture of traditional and modern techniques.
A simple fish scale or bone can tell us a lot about a fish and reveal the fascinating details of its life-history. Fish scales and bones grow bigger as fish get older because a new layer of summer growth is deposited each year, much the same way as the rings of a tree trunk. By counting these layers or rings and the spacing between them, we can determine the age of a fish, its growth rate and other information about its life.
Modern techniques also allow us to examine the chemistry of these structures and to compare their chemical signature with the environment. This allows us to build up a detailed picture of the environments that the fish has lived in and for how long.
The CHASES Project is a collaboration between Inland Fisheries Ireland and the Norwegian Institute for Nature Research (NINA).