HISTORICAL AND PRESENT DISTRIBUTION AND RECENT HABITAT USE OF NASE, CHONDROSTOMA-NASUS, IN THE LOWER JAGST RIVER (BADEN-WURTTEMBERG, GERMANY)

The nase, Chondrostoma nasus, belongs to the autochthonous fish fauna of the Jagst River, where it has generally become rare over the last f ew decades. We conducted literature searches to obtain information abo ut its historical occurrence. For more recent data, we interviewed loc al fishermen, conducted electrofishing surveys, and between 1980 and 1 996, inspected potential spawning sites on the downstream 20 river kil ometres. Historical records suggest that approximately 100 years ago, the nase was found abundantly throughout the Jagst River, and 10 tribu taries also held 'good' populations. However, a recent fish survey for Baden-Wuttemberg lists just 13 sites with known occurrence of the nas e. Only five of these sites were described as having 'abundant' popula tions, but school sizes did not approach the thousands of fish reporte d a century ago. In April 1996, spawning was confirmed for the first t ime at a location two kilometres upstream of the mouth of the Jagst Ri ver. In two electrofishing surveys, the nase represented 4% of the tot al number of fish captured. Despite recent signs of a stabilizing popu lation, the nase is likely to remain threatened by extinction in the J agst River system as long as the majority of the 65 existing barriers continue to hinder the extensive migrations of this species, and water quality problems threaten the survival of the early life stages.