Invasive Alien Signal Crayfish in UK Rivers

Native White-clawed Species Threatened by Disease and Habitat Loss

Jan 3, 2007

European white-clawed crayfish in England are being pushed out by introduced red signal crayfish. Local fishing group and conservationists are working to turn the tide.

The problems caused by invasive alien species are now recognized around the world. But thirty years ago there was much less awareness of how big an effect they could have on native species and their habitat. In the 1970s the American red signal crayfish (Pacifastacus leniusculus) was introduced into England.

Loss of Biodiversity and Habitat Damage

Today in the Brecks, in eastern England, the Lark Angling and Preservation Society (LAPS) and the Brecks Countryside Project are working to protect not just the native white-clawed crayfish (Austropotamobius pallipes), but the overall biodiversity of local rivers. In addition to native crayfish being pushed out, invertebrates and vegetation are disappearing, as the omnivorous signal crayfish consumes everything in sight.

Signal crayfish also burrow deeply into riverbanks and flood control levees, causing the loss of a meter of riverbank a year in heavily infested areas, threatening homes and lives. Rivers become silted and levees are weakened by these deep burrows.

Native White-clawed crayfish

The native white-clawed crayfish is smaller, less aggressive, produces fewer eggs and is out-competed for habitat. The signal crayfish carries a fungus that is usually fatal to the native crayfish species. And, as often happens with introduced species, there are few natural predators to keep them under control.

Trapping Program

The Brecks/LAPS team has spent many hours improving on traps designed for sustainable fisheries to trap the best animals for sending to market. The improvements are intended to make the crayfish traps more effective in capturing other age classes and sizes. Current modifications are capturing more juveniles but they are still working on more effective traps for females carrying eggs and traps that can be incorporated into the riverbank which would prevent further erosion as they catch crayfish. Removing juveniles (crayfish can reproduce within the first year) and females reduces the breeding population. Traps are only used on rivers where there are no native crayfish left.

The next problem to be faced is dealing with the numbers of crayfish caught (over 600,000 in 2005).Luckily, the UK has discovered the culinary value of these invaders. But most of the crayfish eaten in the UK is imported from China and northern Europe. A program is in the works to create a branded environmentally positive food for market. Crayfish is low in fat and high in protein so it appeals to modern dietary preferences.

This awareness raising will set the stage for adding other invasive alien species to the menu.

The copyright of the article Invasive Alien Signal Crayfish in UK Rivers in Wildlife Conservation is owned by Dawn M. Smith. Permission to republish Invasive Alien Signal Crayfish in UK Rivers in print or online must be granted by the author in writing.