Why do we need to understand juvenile fish habitats?
Lessons from the FinVision project
It is 3am on a moonless night in June. In the depths of Plymouth Sound, a small camera springs to life. Its four lenses fix their gaze among the towering seagrass blades, suspended motionless in the gap between tidal ebb and flow. Amid the tiny crustaceans whizzing in the spotlight, a small sand smelt glimmers majestically then, with a panicked fin-flick, is gone. The cause of the sudden departure slowly fades into view: the sculpted flank of a large seabass. Five minutes later, duty done, data stored, camera and lights power down, only to wake again, hour after hour, day after day, in the quest to reveal the roles played by inshore habitats in supporting fisheries.
Are we closing the net on fish habitat needs?
The camera is one of 12 developed for the
FinVision
project – a Fisheries Industry Science Partnership (FISP), funded by DEFRA and led by
Dr Benjamin Ciotti
. Deployed in different habitat types for days or weeks at a time, these cameras are helping us understand what habitats fish need, information critical for designing management actions and policy decisions that underpin viable fisheries and successful nature conservation.
In Europe, more than two-thirds of fish landed in commercial fisheries are known to rely on inshore habitats at some point in their life. Yet coastal areas are on the front line of human impacts such as pollution, habitat destruction and climate change. Notably, habitats like seagrass meadows, saltmarshes and kelp forests, considered to be important fish habitats, have experienced substantial declines along UK coasts. Only with knowledge of fish habitat requirements can we understand how the loss or restoration of habitats impact on fisheries sustainability and nature conservation.
Even the most casual marine biologist will probably have some idea where larger, adult fish live, and century-long records of fisheries catches and scientific surveys provide a tremendous body of data. But the sought-after big fish are reliant on a precarious process of development through egg, larval and juvenile stages which often don’t make it into the survey net. It is small variations in the already minute survival rates of these tiny stages that regulates the size of many fish populations.
Dr Benjamin Ciotti
Associate Professor of Marine Biology
The issue is that young fish need habitats to survive, habitats that are often different from those required by adults. In many cases, it is this juvenile stage that has the tightest reliance on the shallow areas most impacted by humans, yet we know relatively little about the habitat requirements of juvenile fish, particularly the earliest post-larval forms.
The
FinVision
project is innovating new ways to observe, study and gather critical data on easily-overlooked young fish. Bringing together scientists from the University of Plymouth, representatives of the recreational fishing sector (Bass Anglers Sportfishing Society, the National Mullet Club, and the Angling Trust) and management organisations (Association of IFCAs, Southern IFCA, and the Institute for Fisheries Management), a major focus of the project is on developing and testing new camera technology that can film tiny juvenile fish in the wild.
How are cameras helping us to find tiny fish?
The Juvenile Habitat Monitoring Camera (JHaM-Cam) is a smart camera system specifically designed for monitoring juvenile fish. It has been designed and constructed by the University of Plymouth’s
EmbryoPhenomics research team
, in partnership with the Advanced Digital Manufacturing and Innovation Centre, both based at Plymouth Science Park. The camera has specific adaptations which make it perfect for the task. Most importantly, it has a bank of four cameras and integrated lights, enabling 24-hour visualisation of the smallest, thumbnail-sized juveniles that often slip through other surveys.
Run by an onboard computer, JHaM-Cam has impressive power management capabilities and can operate independently on complex tasks of gathering video footage and environmental data for deployments extending over weeks. To set it running, scientists simply configure the deployment regime wirelessly from their mobile phone, before plunging it into their habitat of interest.
Those who have spent happy summer days with nothing more than a net and a bucket may ask why so much tech is needed. People have been catching fish from the sea for millennia, so surely there are easier ways to see where fish are living? Certainly, more traditional approaches such as netting and diver surveys continue to provide essential information about juvenile fish habitat needs. But cameras like the JHaM-Cam are a necessary addition to the toolkit. They are particularly good at spotting the smallest fish that may not be seen by divers, or captured in net surveys, and can be deployed in a range of different habitat types.
Furthermore, the continued day-night, weeklong coverage is critical for capturing finescale changes in distribution. Work in the tropics suggests that habitat use of juvenile fish can be extremely dynamic, with important shifts and key processes occurring at the scale of a few hours. In coral reef fish that settle into juvenile habitats at night, for example, 60% may be lost before morning arrives. Round the clock, long-term coverage increases the chances of capturing these important events. Nature is complex, and therefore innovation must be key to advancing the approaches we use to sample the natural world – particularly when we know that current methods have inherent limitations.
Southern IFCA
As of Spring 2025, JHaM-Cams have been deployed across six habitat types in Plymouth Sound and Tamar Estuary, and alongside a range of other netting surveys stretching from the Fal, Cornwall, to the Isle of Wight. A total of 524 hours of footage, across 73 deployments, has revealed the daily lives of species such as pollack, mullet and seabass.
Data from the deployments is being used directly to advise management measures by the SIFCA and is forming the basis for new approaches to monitoring and research.
Can citizen scientists help with fish habitat research?
As well as providing tools to gather much-needed data, the FinVision partnership is an important opportunity to widen participation in research and connect communities and institutions with the vital ecological role played by coastal habitats. Hosting a number of online and in-person training events, the project also invites members of the public to view footage and record fish sightings through a public web portal hosted by Zooniverse.
A quarter of a million clips have been analysed on the portal so far, further evidence of the staggering contributions that can be made by citizen scientists. Beyond data collection, the web portal represents an important window between two very separate, but interconnected, worlds. The web footage brings the dynamic world of marine creatures into the living room. From the violence of tidal flows, to sublime scenes of colour and tranquillity and murky confusion of coastal habitats, this is the world young fish navigate at the very start of their lives.
Seeing beneath the waves inspires curiosity and educates about the role of marine ecosystems. It also brings a view of coastal habitats into the polling booth, the board room, the council chamber. It is 29 years since the USA, through the Sustainable Fisheries Act (1996), formally recognized ‘Essential Fish Habitats’ in fisheries legislation. Similar legislation does not yet exist in the UK or Europe but momentum is building.
The 2020 Fisheries Act clearly recognises the role ecosystems play in sustaining fisheries, and the recent reorganisation around Fisheries Management Plans provides a mechanism to insert habitat considerations into management actions. Projects like FinVision can advance our understanding of the habitat needs of fish, and will be important to achieving the robust, evidence-based approach required to create sustainable fisheries.
Are you interested in learning more about the project, seeing some of the footage and maybe helping to collect data? Visit
FinVision
to access the interactive web portal and to sign up to receive updates on our research.
This article is adapted from a piece published in The Marine Biologist, April 2025, written by
Dr Benjamin Ciotti
.
Sustainable Aquaculture and Fisheries
At Plymouth, a broad perspective on aquaculture and fisheries management is enabled by our transdisciplinary, systems-thinking approach.
From the health and nutrition of farmed fish, crustaceans and bivalves, to marine conservation, fish tracking, habitats and natural capital, our research explores how all of these diverse elements help contribute towards responsible marine and freshwater food production, and, in doing so, how they support coastal economies and contribute to the national food security agenda.
