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

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.

Asia Conservation Programme

Get the latest on ZSL's conservation work in Asia.

B.U.G.S Blog

Find out more about life in our B.U.G.S exhibit

Remote Sensing in Ecology and Conservation

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

ZSL Shop

See the latest ranges, updates and special offers from our exciting new online shop.

Wild About Magazine

Excerpts from ZSL's award winning members' magazine.

ZSL London Zoo

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

ZSL Whipsnade Zoo

Discover more about the UK's biggest zoo with our fun blog posts!

Discovery and Learning in the Field

Join the ZSL Discovery and Learning team as they venture out of the zoo and in to the wild.


Catch up on our latest Conservation Blogs


ZSL Whipsnade Zoo's elephant keepers give an insight into the daily goings on in the elephant barn.

Tiger conservation

Read about conservation of tigers in Asia.

Videographer Blog

One man is boldly going where no other ZSL videographer has gone before - the land of Mountain Chicken Frogs.

Wild Science

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

Wildlife Wood Project Cameroon

The Wildlife Wood Project has been working in Cameroon since 2007 to encourage better wildlife management in logging concessions.

Penguin expedition blog

Updates from penguin conservation expeditions to Antarctica

Amur Leopard

Amur leopard conservation blog

Baby Giraffe Diaries

Meet ZSL Whipsnade Zoo's latest (and leggiest) arrival, a baby giraffe!

Biodiversity and Palm Oil

Follow the ZSL Biodiversity and Palm Oil team, based in Bogor, Indonesia.

Chagos Expedition

The Chagos marine reserve, designated in 2010 and currently the world’s largest no take marine reserve, is a sought-after spot for marine research.


Science blogs

Tsaobis Baboon Blog

Follow ZSL conservationists studying desert baboons in Namibia.