Sea trout population under threat, UCC research finds

The sea trout population of Ireland could be under threat amid rising temperatures and dwindling food stocks.

Sea trout population under threat, UCC research finds

The sea trout population of Ireland could be under threat amid rising temperatures and dwindling food stocks.

Rising river temperatures see more trout opting to remain inland instead of migrating to sea, according to new research from University College Cork (UCC).

New research from the Environmental Research Institute in UCC shows that more and more stocks of river trout are choosing to remain in rivers rather than undertake the migrations to sea they are known for.

The study focused on Killary Harbour in Connemara, monitoring the movements of trout populations from Tawnyard Lough in the Erriff River in Co Mayo, a population particularly known for its migration.

Increased water temperatures and reduced food supply strongly affected where trout decided to live. More trout are opting to stay in rivers as things heat up.

This could seriously decrease the sea trout population as the climate continues to change.

Little is known about why some fish migrate to sea and others do not. Some brown trout make the decision to leave the river where they are born and head to the sea in search of food or mates, or to get away from unpleasant river conditions. These conditions are likely to be made much worse by climate change, according to the UCC research team.

The researchers looked at how changes in water temperature and the amount of available food influence the migration of brown trout. Both of these factors are heavily influenced by climate change.

By rearing the young of wild trout for two years under conditions of reduced food and increased temperature, and then recording the numbers of future sea-going migrants, the team found that reduced food increases the numbers of migrating fish, but warm temperatures have the opposite effect, where fewer fish choose to migrate to sea, instead remaining resident in fresh water. The study was published this week in Global Change Biology.

Lead author on the study, Louise Archer, of the Environmental Research Institute in UCC, said: "Brown trout are iconic for their ability to undertake impressive migrations to sea, yet we still know little about why some fish choose to migrate, and why others remain resident in fresh water rivers and lakes. What makes a sea trout has been an ongoing source of interest for biologists."

With conflicting pressures mounting, trout will become under increased pressure to make complex decisions about whether they should migrate/

Fish choosing migration are smaller and in poorer condition than those which remain in fresh water, indicating that sea migration occurs when the fish urgently need to consume more food.Striking a balance between seeking food and remaining in warmer waters is the challenge facing the trout.Ms Archer said: "Understanding how climate change will affect migratory sea trout is crucial to successful management and conservation of the species, particularly since many sea trout populations have shown dramatic declines across Europe in recent years. Our study sheds some light on this enduring question by highlighting how warming temperatures cause fewer fish to migrate to sea, with more fish remaining in fresh water to reproduce earlier.

Worryingly, our research suggests that with climate warming, we may see further declines in sea-going trout.

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