Why do we need to monitor freshwater fish?
As part of the wider CaSTCo Project, the Zoological Society of London (ZSL) is carrying out a freshwater fish method audit to understand how freshwater fish are being monitored in the UK and what the future opportunities are for citizen science in the monitoring of freshwater fish. To preface this, this document will outline the importance of monitoring freshwater fish, regardless of whether that monitoring is done with citizen scientists. There are approximately 42 native species of freshwater fish in the UK, as well as several marine species that come into freshwater to breed (Freshwater Habitats Trust 2023). Fish are important in allowing us to gain benefits from freshwater environments and act as indicators of overall river health (DEFRA 2023a). Despite their importance, iconic freshwater fish are declining in the UK and gaps remain in monitoring for some species (The Rivers Trust 2021; UK Parliament 2022a). To better understand how we can conserve freshwater fish, it is important to identify current knowledge gaps and what monitoring should be done to fill them.
Priority habitats and species
Natural England, advisers to the UK government on nature conservation, list rivers and streams as a priority habitat. Priority habitats are those that are most threatened and are important for biodiversity conservation (JNCC 2019b). Nineteen fish species that live in freshwater permanently or to complete part of their life cycle, are listed as priority species for conservation in England (DEFRA and Natural England 2022). Some species are protected under the law meaning that it is an offense to kill, injure or take them (Natural England 2022). Others, you must have a license to fish for, and there are certain national and local rules you must follow (UK Government 2023a). UK regulation protects Special Areas of Conservation and Sites of Special Scientific Interest in areas important for the lifecycles of some priority species (Natural England 2022). The Salmon and Freshwater Fisheries Act and Eel Regulations also both provide significant protections for some species (Salmon and Freshwater Fisheries Act 1975; The Eels (England and Wales) Regulations 2009).
Protection of freshwater fish is important due to population declines of some species. Globally, populations of migratory freshwater fish have declined by 76% since 1970 (WWF 2021). Some UK species are no exception to this trend, with burbot and sturgeon disappearing from UK freshwaters, and others like the European eel, becoming critically endangered. Current data suggests that only 2% of UK Salmon Stocks in England are ‘not at risk’, with 37 out of 42 principal salmon rivers assessed as being ‘at risk’ or ‘probably at risk’ (Environment Agency 2022). In 2020 the government committed to protecting 30% of UK land and sea by 2030 and outlined targets to conserve and enhance biodiversity and halt species declines (Environment Act 2021). Although monitoring will not solve the issues facing these important species, monitoring is still important to better inform conservation that can contribute to reaching these targets. Monitoring is required to measure the effects of both threats and habitat management, which can lead to identification of opportunities for future habitat enhancements and support the reduction of threats on habitat quality.
Fish as indicators of river health
To comply with regulation, the UK publishes figures showing the status of UK waterbodies (UK Parliament 2022a). Recent figures show that only 14% of assessed English rivers met good ecological status and 42% of assessed rivers were at good biological status for fish (UK Government 2023b). To sustain healthy populations, freshwater fish require a certain quality of freshwater river habitat. Fish can be a good indicator of river health, as they respond to changes in water and habitat quality (DEFRA 2023a). By monitoring fish populations over time, we can compare current fish diversity with the expected diversity and the difference can reveal changes in river condition over time. Understanding the biggest drivers of fish populations nationally, such as fishery, industry, and development, can help us regulate these impacts more efficiently, by comparing which management works best to maintain river health.
Ecosystem Services / Natural Capital
Natural capital is the world’s stock of natural resources and ecosystem services are the benefits to humans provided by this natural capital. Overall river health is important due to the ecosystem services provided by freshwater habitats, including natural flood prevention, water abstraction, food supply, pollution removal and recreation (Office for National Statistics 2017). The monetary value of these services was estimated to be around £37 billion in 2012 (Office for National Statistics 2015). Fish play a key role in allowing freshwater habitats to provide these services, serving as vital links in food webs by grazing on plants such as algae, insects, and other fish, as well as providing a food source for larger predators (Everard 2020). They impact their environment by burrowing, ingesting sediment and defecating and are helpful in the cycling of nutrients, by storing, releasing, and transporting sediment around rivers (Office for National Statistics 2015; Villéger et al. 2017). Besides benefiting river health and allowing delivery of ecosystem services, in England the monetary value of freshwater fisheries alone is estimated to be around £1.7 billion per year, with annual spending by anglers of ~£1.6 billion, supporting ~£1.4 billion of additional economic activity (The Rivers Trust 2021). By using monitoring to understand how fish are using freshwater ecosystems in the UK and how factors such as pollution and development are impacting fish populations, we can more easily direct conservation to preserve the function of the services that freshwater habitats provide us with.
Current data & knowledge gaps – what do we need to monitor?
The Environment Agency monitor fish stocks through a variety of methods such as fish counters at weirs and dams, electrofishing surveys for juvenile fish, collecting angling data and through netting, eel traps and hydroacoustic monitoring. This data is publicly available to view on their online data portal (Environment Agency 2023b). Despite a general reduction in Environment Agency grant aid funding, fisheries monitoring by the Environment Agency has remained largely protected, although delivery has been hampered by other factors such as COVID, weather and vacancy restraints (G. Storey, personal communication, September 21st, 2023). The Environment Agency carries out long-term, large scale valuable monitoring on multiple priority species, but some do not fall under the Environment Agencies remit, as responsibility for monitoring species of conservation interest in the UK is shared across the Environment Agency and Natural England. As part of the 25-year Environment Plan, Natural England is measuring the relative abundance and distribution of priority species in England, but fish are not currently included in the relative abundance measure (DEFRA 2023b). As a result, there is large-scale, long-term datasets available on iconic species such as Atlantic Salmon and Brown Trout, but other species have considerably less long-term monitoring effort.
Data is also collected by non-governmental organisations, for example through electrofishing programmes run by Rivers Trusts (South Cumbria Rivers Trust 2019). However, these projects are often also focused on salmonid species. This means electrofishing equipment is set to frequencies that particularly attract and immobilise salmon and trout (e.g., Wye and Usk Foundation, Ribble Rivers Trust, Westcountry Rivers Trust). Other species can be caught alongside, but often more detailed data such as size and condition is only collected on salmonids, with only counts being collected for other species. Although the data on other species can be useful, if the frequency is set to attract salmonids, data collected on other species may not be fully indicative of their population size compared to if species-specific techniques had been used to monitor them. It would be useful to have monitoring schemes set up that focus on other priority species in the UK.
Knowledge of the extent of functional habitat available is important in informing management for all species. Numerous factors influence available habitat to migrating freshwater fish, such as barriers. Extensive data is being collected on this, for example the River Obstacles dataset shows over 55,000 barriers to migration in UK rivers, with the associated citizen science app resulting in continuous contribution to this dataset (River Obstacles 2021). As the effects of climate change become more evident, rivers may be increasingly impacted by factors such as drought, flooding, sedimentation, and increased temperatures. Monitoring will be important in understanding the on-going effects of these impacts on freshwater fish, as well as the effects of parasites and disease. To maximise conservation impact, before monitoring it is important to consider what the data will be used for and how it will be able to inform management and conservation.
In conclusion, the central status of fish within freshwater environments demonstrates the importance of both continuing current monitoring as well as further monitoring to fill knowledge gaps. There is potential for citizen science to assist with the collection of important data on freshwater fish, but increased standardization of methods suitable for citizen science is required to ensure that data collected is robust and impactful. By standardizing methods, collaborating with others and sharing data, we will better be able to enhance biodiversity, restore ecosystem services and conserve freshwater fish and their habitats.
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