Operation and performance of the NESTOR test detector: A measurement of the atmospheric muon flux

NESTOR is a deep-sea neutrino telescope that is under construction in the Ionian Sea off the coast of Greece. In March 2003, a module of the detector was deployed at a depth of 3800m in order to test the overall detector performance and particularly that of the data acquisition systems. Data was continuously transmitted to shore via an electro-optical cable laid on the sea floor. The performance of the detector is described and analysis of the data shows good agreement of the measured cosmic ray muon flux with previous measurements and with phenomenological predictions.