Barriers to Migration

All river fish need to migrate at various points in their life cycle or at various times of year.

Salmon and trout migrate up the small tributaries to spawn in the winter, for example. Adult eels migrate downstream and out to sea to spawn. Meanwhile, many resident species such as barbel, migrate surprisingly large distances to make the best use of feeding opportunities. Other species move up and downstream to take refuge from extreme flows.

The problem for fish

For salmon, the number of juvenile fish a river can produce is proportional the size and quality of available habitat and that ultimately determines the size of the returning salmon run.

In addition, barriers isolate fish populations so that when pollution or catastrophic natural episodes (such as extreme flood or drought) occur, fish and dependent wildlife cannot quickly re-colonise the affected area. This can lead to localised loss or even extinctions.

The situation in the Wye & Usk

The 1975 Salmon and Freshwater Fisheries Act (SAFFA) required that all new weirs and barriers were fitted with fish passes.

Despite this, the Foundation’s early surveys revealed an enormous number of barriers to fish migration: weirs recent and old along with massive timber jams on both rivers. The Lugg and the Monnow (the Wye’s two largest tributaries) were almost completely cut off, save the lowest 10km of the former.

By 1995, 50% of the Wye catchment* was blocked by culverts, debris dams, weirs and crossing points. Our survey of the Usk* (2004) showed that 28% of the river system was blocked by man-made obstructions, in addition to a number of impassable natural falls.

*not including reservoirs

Restoring Access

Restoring access remains the most important and by far the most cost effective river management action that can be undertaken on either river. Since 1996, the Foundation and its partners (particularly Natural Resources Wales and Environment Agency) have embarked on an ambitious programme to reopen the rivers.

Read more about the Foundation’s fish passage work.

Of course, the biggest potential barrier of them all could be Severn tidal power proposals.

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