Invasive species are increasing on Devon rivers.  You should be especially aware of the following:

The Killer Shrimp: Dikerogammarus villosus

Click the link for the NNSS leaflet:  ID_Dikerogammarus_villosus_Killer_Shrimp_v2.1-1

Native to:  SE EuropeHabitat: Still or flowing freshwater

The shrimp is a voracious predator killing invertebrate species and small fish.  It can survive for about 5 days in wet kit and clothing.  It can rapidly dominate an area and significantly alter its ecology.  The photos below show Killer Shrimp(Left) and Freshwater Shrimp (Right)

Signal Crayfish: Pacifastacus leniusculus 

Press the  link below for the NNSS leaflet:

ID_Pacifastacus_leniusculus_Signal_crayfish-1

Native to North America

Habitat:  Fresh water

A very successful invasive species.  They produce large numbers of offspring and will eat practically anything including; invertebrates small fish and even each other.  They are found in holes in the riverbank.  They are found in the river Barle in large numbers and controlling the population has proved difficult.

The Chinese Mitten Crab:  Eriocher sinensis

Press the link below for the NNSS Information Leaflet

ID_Eriocheir_sinensis_Chinese_Mitten_Crab