Wyre our fish struggling?

Amy Blaker is an Early Career Researcher at Lancaster University undertaking her MSc project with WTT’s Prof in Practice. She is taking up the reins of studying impacts of road culverts on fish communities, building upon upon the valuable data already collected by cohorts of MSc students from Queen Mary University of London.

Hidden below the surface of Britain’s rivers and surface waters, our freshwater fish are in trouble! A recent report by the WWF The World’s Forgotten Fishes | WWF (pan​da​.org) revealed a third of global freshwater fish were threatened with extinction. Another report by the World Fish Migration Foundation https://​world​fish​mi​gra​tionfoun​da​tion​.com/​l​i​v​i​n​g​-​p​l​a​n​e​t​-​i​n​d​e​x​-​2020/ highlighted that fish which undertake any form of migration during their lifecycle have declined by 76% globally in the last 50 years, and by a devastating 93% in Europe. Fish play a vital role in our highly connected freshwater and terrestrial ecosystems, contributing to nutrient cycling and energy flow through the aquatic food web. They may feed on invertebrates, algae or other fish, and are an important part of the diets of otters and numerous birds. 

Why are fish populations declining?

A number of pressures face fish and their habitats, but the fragmentation of natural river connectivity is understood to be one of the main causes of decline in freshwater fish species. Anthropogenic modification of rivers by developing high-head structures (i.e. dams and weirs) are obvious barriers for fish passage, impeding movement required for different lifecycle stages such as breeding, feeding, avoiding predation and overcoming competition. But what about low-head structures, such as culverts?

How did the fish cross the road?

Culverts are box or pipe-shaped structures built to allow water to pass beneath road crossings. When poorly engineered, the transition from natural stream characteristics (with heterogeneity in vegetation, rocks and debris), to the smooth concrete walls and base often associated with culverts, presents a physical barrier to fish. Culverts can reduce water depth, increase water velocity and change the turbulence, thereby impeding weaker-swimming fish like European eels and lamprey, or even powerful swimmers adept at leaping like brown trout and salmon from moving upstream and downstream successfully. Furthermore, changes in light availability may create a psychological barrier for fish. The inability to exploit upstream or downstream habitats for reproduction, feeding and the completion of different stages of their lifecycle can lead to weakened populations.

What is being done to understand this?

Here’s where I jump in. Meet the team! I (Amy Blaker) am a MSc student studying Environmental Management at Lancaster University, focusing on water resources. Keen to learn more about freshwater ecosystems, fisheries and restoration techniques, I got in touch with Professor Jon Grey (of Lancaster University and the Wild Trout Trust) who has helped to facilitate this research project with Tom Myerscough (of the Wyre Rivers Trust) to assess the impacts of road culverts on fish populations in the Wyre Catchment. You have probably read previous blogs from teams of Aquatic Ecology MSc students from QMUL – if not, check them out here. 

I will be building upon some of the longer-term data collection at one of our sites, Woodplumpton Brook, but expanding it further and incorporating more sites with similar issues across the Wyre. Not unlike other catchments in the UK, the Wyre is plagued by a number of box culverts which impact the resident and migratory fish communities which call it home. The AMBER (Adaptive Management of Barriers in European Rivers) project is a fantastic source of information on this topic https://amber.international/about/.

We are undertaking primary data collection via electrofishing surveys 50m upstream and downstream of three different sites, ID’ing and measuring each fish before safe release. This will be analysed against secondary data from previous years, which have been collected by Jon, Tom and the MSc Aquatic Ecology students from QMUL. Comparing winter and summer surveys will give a better picture of the seasonal effects of culverts on fish populations. Increased summer temperatures and reduced precipitation induce lower water levels. Not only are temperature sensitive species such as salmon and trout unable to tolerate these conditions, all fish will face increased competition, reduced dissolved oxygen concentration and subsequent stress in smaller volumes of water. Reduced flow and depth through culverts further impedes passage too, exacerbating the difference in fish populations upstream vs downstream.