13th March: Brown trout proven to successfully navigate beaver dams

A groundbreaking study, led by the University of Southampton, has revealed that brown trout can successfully navigate beaver dams – obstacles which were previously thought to pose a significant barrier to their movement.

However, researchers say the situation can be complex, with low water flows in some rivers holding fish below the dams, delaying them from accessing spawning areas. They suggest prolonged dry spells, due to climate change, may increase this problem in certain areas of Great Britain in the future.

Findings are published in the journal PLOS One .

The research monitored trout movements in two streams in Scotland – one modified by a series of four beaver dams and the other unaltered.

The scientists observed the trout as they navigated the barriers during critical spawning periods (October to December). The fish were tracked using telemetry technology, where trout are tagged with microchips that are read by antennae spanning the dam structures.

The researchers found that high river flows, triggered by rainfall, significantly increased the likelihood of successful upstream passage. Additionally, larger fish had greater success at navigating the dams. Conversely, during low flow periods, beaver dams posed a more significant obstacle, delaying or sometimes preventing trout movement upstream.