Pike in Tana river estimated to consume at least 250,000 salmon smolt annually.
Pike in the Tana River consume at least 250,000 Atlantic salmon smolt each year, according to new estimates from researchers at Norwegian Institute for Nature Research (NINA).
The findings are based on analysis of stomach contents from more than 2,000 pike collected in the river system. Researchers estimate that pike consume around 46 salmon smolt per kilogram of pike annually, with smolt making up roughly one third of the predator’s summer diet.
The study comes as the Tana river system, once considered the world’s most important river for Atlantic salmon fishing, has seen a dramatic decline in salmon stocks. The river has been closed to salmon fishing since 2021 following the collapse of the population.
Scientists say several factors may be contributing to the decline, including poor marine survival, overfishing, and predation on smolt during their downstream migration to the sea.
“With the current low production of smolt in the river system, pike predation now represents a much larger share of the remaining stock,” said Martin-A. Svenning, senior researcher at NINA.
The researchers suggest targeted fishing of pike could help reduce predation on salmon smolt. However, they warn that removing too many large pike could have unintended consequences, as larger fish are cannibalistic and help control younger pike that also prey on smolt.
Instead, the report suggests focusing removal efforts on mid-sized pike measuring 40–65 cm, which are considered the main predators of smolt.
Monitoring the age and size structure of the pike population will also be necessary if targeted fishing is introduced, the researchers said, to ensure the measures reduce predation rather than increase it.
