Hampshire chalk streams: surveying their beauty by Hampshire Wildlife Trust

England holds about 85% of the world’s estimated 200 chalk streams. These precious and internationally rare habitats are home to many threatened species.

Hampshire & Isle of Wight Wildlife Trust carries out vital ecological surveys to monitor chalk streams and build a picture of the health of these beautiful waterways. Here, one of the Trust’s trainee ecologists, Mali Valerio, provides an insight into the job.

“Throughout this summer, I have conducted three main types of river surveys: aquatic invertebrates, water voles, and white-clawed crayfish. All these have taken place along the river Itchen and the Candover tributary.

My first survey on the Itchen was ‘kick sampling’ for aquatic invertebrates, which basically means gently disturbing the substrate on the riverbed and recording the wildlife we find. From blue-winged olive nymphs to freshwater shrimps, the biodiversity of aquatic invertebrates gives an indication of how well the river is doing – the higher biodiversity, the better the health of the river. Thankfully, each point we surveyed scored above the threshold.

Water vole surveys are by far the most physically challenging. They involve crawling through the reeds and rushes, combing the riverbanks for any sign of water voles. Unfortunately, I’m yet to find clear evidence of recent water vole activity (though other surveys along the Candover have found water vole signs).

There’s still hope for the Itchen’s water voles though as, despite them facing many challenges like predation from invasive American mink, I found strong evidence of otters on the Itchen, including spraint (otter dung) and fresh fish carcasses. Native otters outcompete the mink, causing a rapid and significant reduction in mink numbers.

Promisingly, we found good numbers of white-clawed crayfish – there are strongholds on the Candover where the species thrive. My job includes helping to record the size and sex of any crayfish we find, plus signs of damage or disease. We then tag individuals with a little capsule in their tail muscle that allows us to identify them on future surveys.

Chalk streams are crucial for white-clawed crayfish as the high calcium content helps them grow their exoskeleton, while rocks filter the water to create crystal clear conditions. However, the new government plans to drastically amend the habitats regulations and scrap policies around nutrient neutrality could impact white-clawed crayfish and entire chalk stream ecosystems.

With chalk stream rivers being so important to our landscape and for the species that call them home, we need to protect them. I can only hope the government realises this before it is too late.”

The Trust celebrates and protects local chalk streams as part of its Watercress & Winterbournes scheme. Learn more at hiwwt.org.uk/watercress-and-winterbournes