Investigation and monitoring of the status of white-legged crayfish – Austropotamobius pallipes –in the Krka NP area

The white-legged crayfish has a natural distribution in all the rivers of the Adriatic basin and also in the Lika region. However, due to a series of pressures and threats to freshwater habitats (deterioration of water quality, the regulation of watercourses, invasive species), the white-legged crayfish has been disappearing from many locations where it was once present

Most of the habitats of the white-legged crayfish are in flowing water, but they also are present in stagnant water. Due to the fragmentation of their habitats, they are unable to migrate significant distances. Therefore, if they disappear from a particular location for any reason, they most often fail to repopulate that location. It can be said that the presence of the white-legged crayfish depends on a continual high quality of the habitat over an extremely long period of time (decades).

The white-legged crayfish spends its entire life cycle in the same type of habitat.

It was last recorded in the Park area in 2003, and was considered to have completely disappeared from this area. It was not until 2023 that 1 individual was recorded again in the Roški Slap area.

The white crab investigation was conducted in 2024, during the summer period, and encompassed a total of 104 localities.

Most locations (86) were investigated by setting up traps, while a smaller number of locations (18) were surveyed by visual observation. In addition to the Krka River, the investigation also included its tributaries.

The research results showed that in the Krka River basin, white-legged crayfish were recorded at 9 out of 104 investigated locations.

The population under the Krčić waterfall is numerous, but extremely limited spatially. The populations at Roški slap waterfall and Visovac Lake are rare. The situation in the tributaries of the Krka River is somewhat better, with dense populations found along the watercourses of the Bribišnica and Vrba.

Despite the resurgence of white-legged crayfish, the populations are isolated and extremely vulnerable due to the presence of various stress elements. The greatest threats to the survival of white-legged crayfish are polluted water, the crayfish plague, and various invasive species.

Monitoring the condition of the white-legged crayfish in the area of ​​the Krka River will continue, and the possibility of reintroduction is also being considered.