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Burrishoole sea trout census
We monitor sea trout in the Burrishoole system to understand population trends, migration patterns, and survival. This long-term dataset supports research on fish life cycles, recruitment, and environmental pressures.
Life cycle and migration
The Burrishoole traps have recorded sea trout moving upstream and downstream since 1971. Young sea trout, known as smolts, migrate to sea between March and May. Some return in the same year as finnock, while others spend a full year at sea before returning as larger adults. These different life histories help researchers study growth, survival, and marine conditions.
Decline in smolt numbers
Historically, annual smolt numbers ranged from 2,337 to 6,710 fish. After 1990, the record showed a strong downward trend, reaching its lowest recorded count of 263 smolts in 2010. Numbers have remained consistently low since 2001.
The decline points to serious issues with spawning success and recruitment. Current smolt output is at its lowest level on record, raising a key concern for stock sustainability.
Adult returns and stock collapse
Returns of finnock and adult sea trout have remained low since a major stock collapse in 1989 and 1990. Before 1989, the population typically ranged from 1,000 to 2,500 fish. Since the 1990s, annual returns have fallen to fewer than 100 fish, and the spawning stock is now at a very low level.
Despite long-term monitoring, the population has not recovered to previous levels. Burrishoole is therefore a critical case study for understanding stock collapse and barriers to recovery.