Another crustacean crisis

Due to the sustained period of dry and hot weather recently an emergency rescue was required last week. We’ve blogged about similar operations in the previous two years, where the River Rye in Duncombe Park, Helmsley tends to dry up during summer months because of numerous natural sink holes. This leaves large numbers of fish and other water-dependent creatures stranded in shrinking pools. This year the crisis was particularly acute with no effective quantities of rain in the short term weather forecast.

The River Rye is one of only a few rivers in the North East of England which supports a population of White-clawed crayfish (Austropotamobius pallipes). The species are “Globally Threatened” according to the IUCN’s Red List of Threatened Species. They are the only native crayfish in the UK, and the majority of populations here are declining due to competition from introduced crayfish species, crayfish plague and water pollution.

So last week, alerted by the local fishing club, staff and apprentices turned up in force under the supervision of Simon our River Esk Officer (because he has a licence to handle the protected crayfish). Using gloves and buckets everyone scooped up what creatures they could and then relayed the buckets upstream to where the collected creatures were released back into the River Rye, safely above the sink holes. Over 500 White-clawed crayfish were rescued along with a variety of fish species – Bullhead (250+), Brown Trout (20+), Stone Loach (20+) and Brook Lamprey (50+).

The translocated fish and White-clawed crayfish will inevitably recolonise the dried up section once the flows return to normal. The habitat here is ordinarily really good, the only down side being the disastrous disappearing water phenomenon during the summer.

The future for local White-clawed crayfish is somewhat uncertain. Further survey work is needed to establish the location of populations in the Rye, in order to help direct and prioritise effective measures to bolster the populations and make them more resilient to climate change risks like flash flooding and drought crisis. Rescue events may need to become a regularised occurrence.

We have no current evidence that the introduced Signal crayfish, which are such a threat to the White-clawed crayfish, have made it into the River Rye yet. Elsewhere in the country ark sites have been established, away from river networks, where populations of White-clawed crayfish can be introduced and kept in blissful isolation. If feasible here this could be a useful additional safety measure, but the first priority is keeping the Rye White-clawed crayfish populations in the river for as long as possible and conserving this particular element of our local natural heritage.