Microhabitat suitability as a tool to improve the success rate of a translocation or reintroduction, case‐study of the bullhead (Cottus perifretum) in Flanders, Belgium.

Microhabitat suitability models are useful tools to enhance the reintroduction success of fish. Since 2008, a translocation and reintroduction program has been carried out in Flanders to prevent substantial loss of genetic variability in the Cottus perifretum (bullhead) population, and to meet the goals set by the Habitat Directive. To this end, habitat suitability of potential headstreams was assessed on a macrohabitat and microhabitat scale prior to the reintroduction. On a macrohabitat scale, water quality, habitat structure, food availability, and fish community were screened. Based on microhabitat models for bullhead in the summer period, microhabitat suitability was assessed in headstreams where macrohabitat characteristics showed a high potential for success. Both macro‐ and microhabitat assessment showed that reintroduction of bullheads in the Nellebeek, Bruelbeek, and Mollendaalbeek would most likely lead to self‐sustaining populations. For the Sint‐Annabeek, the microhabitat suitability model, considering depth and stream velocity, estimates that 7.5–9.5% of the headstream is suitable for bullhead. However, when substratum is taken into account, the microhabitat suitability index shows that only 4.3–5.8% of the brook is suitable. The current habitat quality and quantity in the Sint‐Annabeek is estimated to support a mean total population of 812 bullheads. However, the microhabitat suitability can be substantially improved by the artificial deposition of medium‐sized gravel (5–50 mm) and large gravel (50–100 mm). By doing so, the mean estimated population size could increase up to 1,330 individuals. Our results show that habitat improvement is necessary prior to the reintroduction of bullheads in the Sint‐Annabeek. [ABSTRACT FROM AUTHOR]