Twaite Shad, UK's Rarest Fish, Returns to River Severn to Breed

On the River Severn, one of the UK's rarest fish has a chance to return to its historical spawning grounds.

Twaite Shad

The twaite shad (Alosa fallax), a herring family member, was once abundant in British rivers, with thousands of fish spawning upstream in the spring.

Overfishing, deforestation, habitat loss, and migratory path obstruction have all contributed to population declines. Hybridization between species is more common in species that have been disturbed by humans. The estuarine period, or the time they spend in estuaries swimming from spawning grounds to sea, is expected to last up to a year and a half in A. fallax. Specific heterogeneity and juvenile survival in the estuarine phase are not taken into consideration in the calculation.

Restoring its Breeding Grounds

By constructing routes through many weirs, a restoration scheme attempts to open up the river to fish.

The restoration is expected to help a variety of animals, including salmon, lamprey, and eels.

The twaite shad may return to stretches of the river north of Worcester this month.

Volunteers are required to listen to the fish's characteristic splashing noises as they spawn at night.

The Canal & River Trust's program director, Jason Leach, said: "Giving nature a chance to heal is never too late.

"Our project's riverside spawning vigils at night are a fitting way to start documenting the survival of the fish that were harmed so severely when our forefathers built the weirs unwittingly, causing a major problem for migratory fish.

Conservation Efforts

In Ireland, four special protected areas have been named where Alosa species have been found to spawn. Twaite is included in Appendix III of the Bern Convention (1979), which lists endangered fauna species, and in Appendices II and V of the European Community Habitats Directive (1992), which list species whose protection necessitates the establishment of particular conservation areas and species that are subject to management steps, respectively.

"We're hoping that a large number of volunteers will be motivated to join us in seeing and recording the spring shad-spawning phenomena."

Continuing Efforts

The Key to Success The Canal & River Trust, Severn Rivers Trust, Environment Agency, and Natural England are working together on the Severn initiative to reopen 150 miles (241 kilometers) of the river to fish.

At Diglis and Bevere, near Worcester, two specially built passes alongside Victorian-era weirs have been completed.

According to a report conducted by Swansea University, walls such as weirs, bridges, hydropower systems, and culverts have fragmented 99 percent of the UK's waterways.

Migratory fish find it impossible to complete their journeys to multiply and find food due to the high number of barriers.

"Imagine a 10cm long fish, and a barrier even less than 50cm wide would keep that fish from traveling up and down the river to various bits of habitat where it could eat or spawn," said researcher Dr. Joshua Jones.