Fish ‘suffocating in the heat’: Exeter experts comment on UK’s hottest June

University of Exeter scientists have commented on the environmental impacts of the UK’s hottest June on record.

According to the Met Office, the UK average mean temperature in June was 15.8°C – the highest in records going back to 1884, and 0.9°C above the previous record.

This week, the Wildlife Trusts said June’s hot weather caused unprecedented deaths of fish in rivers and disturbed insects and plants.

Researchers at Exeter – which has a team of over 1,500 environment and climate experts – have echoed these concerns.

Professor Richard ffrench-Constant, from the Centre for Ecology and Conservation on the Penryn Campus in Cornwall, said: “Just like us, fish need oxygen, but warm water holds less oxygen.

“This means that not only are fish facing a cocktail of sewage, fertilisers and pharmaceuticals – in rivers already devoid of oxygenating plants – but now they are effectively suffocating in the heat.”

He added: “The hottest June on record has been strangely quiet for insects. So, Hawthorn blossom was amazing but completely devoid of any insects.

“Now that it’s July, insects are picking up again. I suspect that insects at specific life stages (eg caterpillars) are very prone to drought.

“Although the ‘June gap’ in butterflies is well known (the gap between the early and late species) this year June was quiet for all insect groups.

“The persistent high pressure over the UK may also have contributed as it could have stalled the usual influx of hoverflies and the usual insect migrants from the continent.

“Low numbers of insects in June would be expected to directly affect bird nesting success as this is the stage when they are actively feeding young.”

Professor Richard Brazier, Co-Director of the Centre for Resilience in Environment, Water and Waste (CREWW), said: “We have seen six of the warmest years ever in the last decade, and it is no coincidence that we have also seen a number of drought years, both this year and last year.

“If the temperatures get into the 30s regularly, it is not just drought that will cause problems though.

“The heat stress for a number of plants and animals, including humans of course, will be arguably more significant than the lack of water.”

Asked whether any specific animal species suffer from this sort of heat, Professor Brazier said: “Most species that are not mobile and cannot seek refuge from excess heat will suffer, especially aquatic species that run out of water – think amphibians such as frogs whose ponds dry up.

“They will perish but also all the species that would eat them will suffer.

“This problem, where the base of the food pyramid is removed by excess heat or lack of water, is perhaps more significant than the air temperatures or the direct distress caused by the heat.”

And commenting on risks to plants, he added: “Most temperate plants are not well adapted to excess heat or prolonged drought.

“We will see many tree species shedding their leaves earlier than normal, and in worst-case scenarios succumbing to disease or pests as they are less resilient to both when they are water stressed.

“Of course, some species might thrive – woody species with deeper roots doing better than grasses which are shallow rooted.

“The problem that plants have is that they cannot move at all to respond to climate change, so those species that do well in warmer and drier climates will dominate, for example oaks, whereas those shallow-rooted trees such as beech may struggle.”

Dr Ilya Maclean, from the Environment and Sustainability Institute, said: “Most wildlife in the UK is well adapted to the climatic conditions we have experienced historically.

“However, in the last few years we are increasingly witnessing conditions that are without recent historic precedent, which poses a significant challenge for wildlife.

“In extreme cases, species can literally die of heat stress. Some animals and plants simply cannot withstand extreme temperatures and die as a result.

“In less extreme cases, hot and dry conditions force animals into taking evasive action – for example by seeking out shady conditions.

“However, this disrupts their normal patterns of feeding and breeding behaviour, with longer-term implications for their survival.”