Atlantic salmon

This autumn Simon King visits the River Tay in Scotland to investigate the lives of the spawning Atlantic salmon.

More about the species

The Atlantic salmon is a muscular fish with silvery colouration and black spots. They have a small fatty dorsal fin and a tail fin and can be up to about 150cm long and weigh over 20kg, although this is rare. The mouth extends to below the eye or beyond. In males during the breeding season the lower jaw develops a hook shape for fighting. Adults also take on a reddish colour around this time.

Atlantic salmon are anadromous which means that they migrate from the sea to fresh water to spawn. The juveniles feed on aquatic insects and invertebrates in freshwater. When they migrate to the sea they start to feed on crustaceans and fish.

Salmon eggs are fertilised externally by the males. The female will dig a pit in the gravel (known as a redd) on the riverbed in which she deposits up to 900 eggs. A male will immediately follow and fertilise them before she covers them over using her tail. About 90–95% of the salmon will die after their first spawning but some are known to spawn several times, returning to the ocean to feed between spawnings.

The salmon are thought to spawn during conditions of appropriate temperature and daylight and so spawning varies in time between rivers. Most spawning occurs between November and December but some larger rivers have been known to host spawning salmon from October through to February.

Around 50% of Atlantic salmon populations in the UK are at risk due to a lack of pristine river systems, migration obstacles such as dams, fishing and climate changes affecting their biology.