Comparison of two different field cages for semi-natural rearing of juvenile freshwater pearl mussels, Margaritifera margaritifera (Linnaeus, 1758) (Bivalvia: Unionoidea: Margaritiferidae)

Abstract

Due to a lack of natural recruitment, the freshwater pearl mussel is on the brink of extinction in many parts of its distribution area. As a consequence, several breeding programs are in operation, many of them using semi-natural rearing methods. Especially during early life stages, several types of rearing devices are used to raise juveniles. However, there is no systematic comparison of different devices. In our experiment, we compared Buddensiek cages and sediment boxes. Each rearing device was filled with 30 one-year-old individuals. At 10 sampling sites three Buddensiek cages and three sediment boxes were exposed. Exposure started in June 2016 and ended in May 2017. Overall, survival of juveniles was higher in Buddensiek cages than in sediment boxes with 40–93% compared to 0–87%. Growth was comparable in both field cages. The study site specific variation indicates that suitability of field cages is determined by environmental conditions. Furthermore, handling effort differs between the tested field cages. The optimal operating conditions for each field cage are discussed.