DO DIFFERENT PREDATORS AFFECT DISTANCE, DIRECTION AND DESTINATION OF MOVEMENTS BY A STREAM MAYFLY

We observed the directions and distances travelled by Nesameletus orna tus mayfly nymphs in stream channels (current velocity 18 cm.s(-)1) wi th either Eldon's galaxias (Galaxias eldoni), brown trout (Solmo trutt a), or no fish. Short (<20 cm) upstream movements were most common, bu t movements up to 90 cm in both directions were recorded. Predators ha d no significant impact on movement direction or distance compared wit h controls when all movements were considered. Only movements in direc t response to galaxas were significantly longer and more likely to be in a downstream direction than movements not directly associated with galaxias. In most cases the frequency of downstream drift distances fi tted a negative exponential model. Our results showed that when curren t and turbulence were low, N. ornatus could have considerable control over their movement.