Life in the Thames: Tales from the field

by ZSL on

Did you know that since 1964, 125 species of fish have been reported in the Tidal Thames, and that some of these species’ spawn and their eggs might be drifting with the tide while you are crossing the river?

Clara Obregon, ZSL Europe Junior Conservation Biologist, blogs about her experience carrying out field work in the Tidal Thames. 

Jennifer McCard and Clara Obregon with juvenile European smelt
Jennifer McCard and Clara Obregon with juvenile European smelt

After working for more than a year with ZSL in the Tidal Thames, it still amazes me that a river supporting a city of more than 8 million inhabitants has such diverse marine and freshwater wildlife. Besides the marine mammals coming in and out from the mouth of the estuary to the upper Thames region; there are also more than 120 species of fish reported in these waters. Some of these species don’t even look like they could live in cold waters, such as the Corkwing wrasse (Symphodus melops) and short-snouted seahorse (Hippocampus hippocampus), which were both sampled at the Tidal Thames. 

ZSL's Thames Conservation Programme is working with partners, citizen scientists and volunteers to further improve the ecology of the Tidal Thames and the wider river catchment. The work also aims to conserve and further understand the population dynamics of these species. 

Why are we making a Juvenile Fish ID Guide for the Tidal Thames? 

One project we are currently working on is focused on the larvae and juvenile fish present in the Tidal Thames. Last year we did weekly ichthyoplankton and seine netting surveys, focused on catching the European smelt (Osmerus eperlanus) – the fish that smells like cucumber! During the ichthyoplankton surveys we mostly caught the target species, smelt fry (juvenile European smelt) and eggs.  

However, during the seine netting surveys, a larger variety of different species were found. The challenge with fish in their Early Life History Stages (ELHS) is that they are quite hard to recognise from one another! Luckily, we had help in the field from Environment Agency, the Institute of Fisheries Management and Bournemouth University, to guide us and train us on how to identify the main species we were finding.  

Having had this experience and knowing that we would be continuing our conservation work on ELHS fish in 2017, we decided to produce a Juvenile Fish ID Guide for the Tidal Thames. This ID Guide was kindly funded by the Heritage Lottery Fund and has been produced to help with the identification of larval and juvenile developmental stages of fish in the Tidal Thames.  

Thames fish

The power of collaboration 
Working with partners from across the country, we have gathered information on the most common species found in the Tidal Thames in Greater London. Our partners have kindly shared their field photos and, together with the ones we had from our field surveys, we have gathered pictures of more than 30 species in their ELHS. 

The species listed in this ID Guide are most commonly found in the Tidal Thames in Greater London. However, this guide can be more widely used to inform fish identification in estuarine waters around the UK. It has been designed to enable conservation practitioners, scientists, consultants and citizen scientists to better identify ELHS in the field, and where taking samples for observation under a microscope is not possible. We hope it will be useful for anyone keen to get their feet in a river and observe the fish living in it, either here in London or somewhere else! 

Find out more about the project 


This project was made possible with thanks to funding from the Heritage Lottery Fund (HLF). We are very grateful for the help of Steve Colclough from the Institute of Fisheries Management (IFM) and Tom Cousins and Peter Gray from the Environment Agency (EA) who provided advice on which species to include in this guide and tips for their identification.  

Additional thanks go to Jamie Craggs (Horniman Museum), Andy D. Nunn (University of Hull), Neil Garrick-Maidment (The Seahorse Trust), Gareth Jones (Ribble Rivers Trust), Pete Liptrot (Bolton Aquarium), John Newman (Horniman Museum), Paul Peters (Ribble Rivers Trust), Adrian Pinder (Bournemouth University), David Powell (Environment Agency) and Katherine Tye (Environment Agency) who provided invaluable photos and expertise of various species to use in this Guide.


Select a blog

Careers at ZSL

Our people are our greatest asset and we realise our vision for a world where wildlife thrives through their ideas, skills and passion. An inspired, informed and empowered community of people work, study and volunteer together at ZSL.

Nature at the heart of global decision making

At ZSL, a key area of our work is the employment of Nature-based Solutions – an approach which both adapt to and mitigates the impacts of climate change. These Solutions, which include habitat protection and restoration, are low-cost yet high-impact, and provide multiple benefits to people and wildlife. We ensure that biodiversity recovery is at the heart of nature-based solutions. 

ZSL London Zoo

A blog for lovers of ZSL London Zoo, bringing you extraordinary animal facts and exclusive access to the world's oldest scientific zoo.

ZSL Whipsnade Zoo

Do you love wildlife? Discover more about our amazing animals at the UK's biggest zoo!


We're working around the world to conserve animals and their habitats, find out more about our latest achievements.


From the field to the lab, catch up with the scientists on the cutting edge of conservation biology at ZSL’s Institute of Zoology.


A day in Discovery and Learning at ZSL is never dull! The team tell us all about the exciting sessions for school children, as well as work further afield.

Artefact of the month

Every month, one of the pieces held in ZSL’s Library and at ZSL Whipsnade Zoo will feature here as Artefact of the Month.

Wild About

Read testimonials from our Members and extracts from ZSL's award winning members' magazine, Wild About.

Asia Conservation Programme

ZSL works across Asia, from the famous national parks of Nepal to marine protected areas in the Philippines. Read the latest updates on our conservation.

Remote Sensing in Ecology and Conservation

An Open Access journal for research at the interface of remote sensing, ecology and conservation.