Waterpeil een sleutelfactor in de levenscyclus van de grote modder kruiper

Water level, a key factor in the life cycle of the weatherfi sh From March 2012 until May 2013 we studied the weatherfi sh (Misgurnus fossilis) in two ditches. In each ditch PIT tags were implanted in adult animals. During most months 2-4 research rounds were carried out with a mobile antenna to determine the position of the tagged animals. The migration behaviour and loss of animals di­ ered between the two ditches. In one ditch the animals migrated in spring (March- April) from the only deep part to the shallow vegetated upstream part.They moved many hundreds of meters up to 1,5 km each month (monthly average 300- 800 m).They went back (July 2012) at a strong decline in water level when 95% of the ditch fell dry. In the other ditch with only little variation in waterlevels the animals moved less (monthly average 100-300 m). In the ditch with a strong decline in water level a lot of animals disappeared (44%), mainly during the period of dry fall (August- November). We found strong evidence that they were predated by birds and mammals. From the ditch with small di­ erences in water level fewer animals disappeared (10%). No 0+ juveniles were caught during multiple electro and dip net samplings in 2012 and 2013 in either ditch. The lack of spring fl oodings seems to be an important cause for the po0r reproduction of the species.