Work

Evaluation of the stocking efficiency of a rheophilic cyprinid in a large river system using spatio-temporal PIT tag detections and survival analysis

Year: 2026

Type: article

Abstract: The common nase ( Chondrostoma nasus) was a formerly abundant European riverine fish that has suffered a steep decline due to anthropogenic influences. To address this decline, stakeholders initiated a stocking program for this species in the River Inn, Germany. To evaluate stocking success, 1650 hatchery-raised age 1+ and 2+ juveniles were tagged with passive integrated transponders (PIT tags), released into three habitat types (backwaters, fish passes, and mainstream), and monitored over 2 years using 38 fixed antenna arrays distributed over 150 km. Detection rates decreased substantially over time, but still reached 7.2% after 2 years. A continuous-time survival model revealed that survival rates were lowest immediately after stocking but stayed relatively constant after an acclimatisation phase of 240 days. Nase used all habitat types and accumulated in areas with greatest habitat diversity including nature-like fishways. Our results highlight that the selection of the stocking site had a measurable effect on survival. They also suggest that a combined optimisation of stocking and restoring of diverse riverine habitats is likely to increase the efficiency of nase conservation programs.

Source: Canadian Journal of Fisheries and Aquatic Sciences

DOI: 10.1139/cjfas-2025-0337

Authors: Jan Droll, Christoffer Nagel, Joachim Pander, Juergen Geist

Institution: Technical University of Munich

Language: English

Topic: Fish Ecology and Management Studies

Subfield: Nature and Landscape Conservation

Field: Environmental Science

Domain: Physical Sciences

SDG: Clean water and sanitation

Open Access status: hybrid

Funder: VERBUND Innkraftwerke