Articles & Case Studies

Working with ZSL to help conserve smelt in the Tidal Thames

Posted: Wednesday 16th November 2016

Smelt are small, predatory fish that were once very common, but whose numbers have declined significantly since the early 19th century, disappearing from many UK rivers. The fish has been recognised as a priority for conservation, and ZSL (Zoological Society of London) is helping to conserve the smelt in the Tidal Thames which has a small, but nationally significant population.

The smelt (Latin name: Osmerus eprlanus), which is known for its distinct smell of fresh cucumber, takes its name from the ancient Anglo-Saxon word "smoelt" meaning smooth and shining. Typically around 15-18cm in length, the smelt is a slender, bright silver fish, grey-green to pink on its back and sides, which can live for up to six years.

The decline of the smelt population has been caused by a number of factors: water pollution, over exploitation and engineering changes to rivers which affect up-river migration and spawning habitats. Thanks to improvements in water quality in the second half of the 20th century, smelt have returned to a few rivers in England, including the Thames. Nevertheless, the fish is still considered significantly threatened, due to its rarity, and there has been little conservation action to date.

Until recently, the river habits of smelt, and the precise locations of their spawning grounds in the Thames have been unknown. ZSL, The Institute of Fisheries Management, Bournemouth University Global Environmental Solutions, and HR Wallingford, have undertaken a collaborative project to investigate how juvenile smelt fry use the Tidal Thames, and to identify important habitats for their conservation. The project has been supported by the National Lottery through the Heritage Lottery Fund.

ZSL provided data collected during its 2015 and 2016 survey seasons which HR Wallingford scientists, Tom Benson and Kate Rossington, used to carry out numerical modelling using the TELEMAC flow model of the Thames Estuary, in combination with an Individual Based Model (IBM), used to track simulated smelt hatchlings.

ZSL held a Smelt Celebration Event at ZSL London Zoo on 20 October 2016 at which the results of this survey work were announced.

Tom Benson, Senior Scientist at HR Wallingford, said: "We are delighted that our numerical fish modelling has helped to locate the spawning grounds of smelt which have turned out to be close to Wandsworth Bridge. The modelling has also revealed useful information about how juvenile smelt fry use the estuary, and identifying their habitats will help conserve them in the region."

Joanna Barker, Europe Conservation Project Manager at ZSL added: "This collaborative project is a great example of how partnership working leads to tangible conservation outcomes. The combination of HR Wallingford's modelling work and more traditional analysis, has provided the data needed to conserve this important fish species in a busy urban estuary. It has also led to the development of a guidance document which focuses on how to conserve fish through the planning process in the Tidal Thames."

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