Tidal Thames fish conservation

Smelt getting measured in the thames

Tidal Thames fish conservation

The Tidal Thames, from Teddington Lock eastwards to Gravesend, is an important estuarine ecosystem, vital for a number of fish species including many of commercial and ecological significance.  The estuary provides valuable nursery habitat for juvenile fish, an essential pathway between marine and freshwater habitat for migratory species and appropriate conditions for certain fish to spawn (lay eggs).  These qualities combine to make the Tidal Thames a zone of national importance for fish conservation.

In the period since 1964, following substantial improvements in water quality, 125 different species of fish have been recorded as occurring in the Tidal Thames.  However, like other complex estuarine habitats, this region remains poorly studied and there is a need to further our understanding of the ways in which fish are using the river in order to protect vulnerable populations from continued threats such as poor water quality and development activities.

Thames fish conservation

Providing management guidance

ZSL is working to ensure that important life stages of fish species and their habitats are protected in the Tidal Thames. With this aim we have published a Guidance Document  on Conservation of Tidal Thames fish through the Planning Process. This document provides a single point of reference to Developers , Planners, Biodiversity Officers and Consultants on how Tidal Thames fish should be considered when planning developments on or beside the river.

Focus on the European smelt

The European smelt, Osmerus eperlanus, which smells curiously of cucumber, is a small predatory fish that inhabits cold-water estuaries. This species supported an important fishery in the Thames estuary through to the 19th century but subsequently suffered severe declines throughout the UK, and was lost from the Thames, along with all other fish species, when the river was declared ‘biologically dead’ in the 1850s.  The Thames Times  leaflet was produced to help share knowledge of this economically significant cultural heritage with Londoners.  Detailed accounts of the history of the smelt fishery can be found on our Riverpedia.  

Smelt is considered a valuable indicator species due to its sensitivity to pollution, and it is a positive sign that the species has returned to 36 water courses in England including the Tidal Thames in the 20th Century.  The species remains rare in the United Kingdom and is recognised as a Feature of Conservation Importance (FOCI) for Marine Conservation Zones (MCZs) designated under the Marine and Coastal Access Act 2009 (MCAA).   The smelt population in the Thames is currently believed to be one of the largest breeding populations of the species in the UK.

From 2014 through to 2016, with support from the Heritage Lottery Fund, ZSL has conducted a study of smelt in the Thames. Through the results of our surveys and using hydrodynamic models in collaboration with HR Wallingford, it has been possible to narrow down the potential spawning location of smelt to a 600m stretch of the Thames in central London.

Thames fish conservation

Ongoing work

Over the coming years ZSL will continue to monitor the juvenile stages of fish species utilising the Tidal Thames, working in partnership with Bournemouth University Global Environmental Solutions (BUG) and Colclough & Coates (SC2), with support from Tideway.   These studies will provide a benchmark to measure the health of the fish populations over time and with expected improvements to water quality.  Along with further ichthyoplankton and seine-netting surveys, we will continue to train and work with citizen science volunteers who will have the opportunity to support our foreshore-based survey work . Please email marineandfreshwater@zsl.org if you would like to get involved.

Monitoring fish at power stations

Between 2006 and 2013 ZSL completed long-term monitoring in collaboration with Tilbury Power Station and the Environment Agency.  Regular weekly monitoring of fish species passing through the Tilbury Power station has provided data enabling a better understanding of which fish species are regularly using the Thames Estuary. This study was also designed to allow detection of changes in fish abundance or species composition, including occurrence of any new or rare species.

Thames fish conservation


Project information

Key species

  • European smelt (Osmerus eperlanus)
  • European eel (Anguilla anguilla)
  • Common dace (Leuciscus leuciscus)
  • Common goby (Pomatoschistus microps)
  • Dover sole (Solea solea)
  • European seabass (Dicentrarchus labrax)
  • European sprat (Sprattus sprattus)
  • Flounder (Platichthys flesus)
  • Herring (Clupea harengus)
  • Nilsson’s pipefish (Syngnathus rostellatus)
  • Pouting (Trisopterus luscus)
  • Roach (Rutilus rutilus)
  • Sand goby (Pomatoschistus minutus)
  • Whiting (Merlangus merlangus)

People Involved

Joanna Barker manages ZSL’s work on fish conservation in the Tidal Thames.  Joe Pecorelli coordinates participation by volunteer citizen scientists and researchers.

Partners and sponsors

  • Bournemouth University Global Environmental Solutions (BUG)
  • Colclough & Coates (SC2)
  • Creekside Education Trust
  • Environment Agency 
  • Heritage Lottery Fund 
  • HR Wallingford
  • Institute for Fisheries Management (IFM)
  • Port of London Authority (PLA)
  • RWE nPower
  • Thames Explorer Trust
  • Tideway