West Country fish 'suffocating' in rivers after hottest ever June on record

Fish are struggling due to the increase in temperatures. Credit: PA Images

Fish in the West Country are 'suffocating' in rivers due to the hot temperatures, according to scientists at the University of Exeter.

Last month was the UK’s hottest June on record. The average mean temperature for the month was 15.8°C – the highest in records going back to 1884, and 0.9°C above the previous record.

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.”

Professor ffrench-Constant also believes insects have been affected, which has a direct impact on nesting birds trying to feed their young.

A pair of Bewick's swans at Slimbridge Wetland Centre. Nesting birds will be affected by the impact of hot weather on insects. Credit: PA Images

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."

The heat is also set to have an effect on plants and aquatic species that will not be able to move when water supplies dry up.

Professor Richard Brazier, Co-Director of the Centre for Resilience in Environment, Water and Waste (CREWW), spoke of what will happen if the temperatures get into the 30s regularly.

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

“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.”

A common garden frog - one of the species that could be affected by hotter temperatures. Credit: PA Images

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, says the conditions that are now being experienced pose a "significant challenge" for wildlife.

Dr Maclean said: “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.”