Fish weir

A fishing weir, fish weir, fishgarth or kiddle is an obstruction placed in tidal waters, or wholly or partially across a river, to direct the passage of fish. A weir may be used to trap fish such as salmon as they attempt to swim upstream, or eels as they migrate downstream. Alternatively, fish weirs can be used to channel fish to a particular location, such as to a fish ladder. Weirs were traditionally built from wood or stones. The use of fishing weirs as fish traps dates back prior to the emergence of modern humans, and have since been used by many societies across the world.

The word weir comes from the Anglo-Saxon wer, one meaning of which is a device to trap fish. The use of stone tidal weirs to catch fish has a long history dating back to the pre-sapiens phase of hominid evolution. In Ireland, fish traps in association with weirs have been found that date from 8,000 years ago. Stone tidal weirs were used across the world and by 1707, 160 such structures, some of which reached 360 metres in length, were in use along the coast of the Shimabara Peninsula of Japan.

In medieval Europe, large fishing weir structures were constructed from wood posts and wattle fences. V-shaped structures in rivers could be as long as 60 m and worked by directing fish towards fish traps or nets. Such weirs were frequently the cause of disputes between various classes of river users and tenants of neighbouring land. Basket weir fish traps are shown in medieval illustrations and surviving examples have been found. Basket weirs are about two metres long and comprise two wicker cones, one inside the other — easy for fish to get into but difficult to escape.

In September 2014 researchers from University of Victoria investigated what may turn out to be a 14,000-year-old fish weir in 120 ft of water off the coast of Haida Gwaii, British Columbia.

In Great Britain the traditional form was one or more rock weirs constructed in tidal races or on a sandy beach, with a small gap that could be blocked by fences when the tide turned to flow out again. Surviving examples, but no longer in use, can be seen in the Menai Strait. Another ancient example was at Rhos Fynach in North Wales, which survived in use until World War I.

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Wikipedia