Distribution, upstream migration and habitat selection of maturing lampreys, Geotria australis, in Pigeon Bay Stream, New Zealand

Abstract

Adult lampreys, Geotria australis, began to enter Pigeon Bay Stream just before 7 August 1992. Lampreys moved upstream more or less en masse, because adults were found immediately above the tidal limit in August but at the mouths of headwater streams in late October. Capture rates of adult lampreys in fyke-nets were irregular and appeared to reflect the movement of the fish through stream sections as upstream migration occurred. The daily distance travelled by lampreys individually equipped with radio transmitters declined from a high of 87.8 m to 0 m between August and November. Lampreys typically selected the spaces formed under boulders, usually 25 cm in diameter, at the bottom of riffles and at the upstream ends of pools. With only one exception, lampreys were never seen above the surface of the substratum. Movement occurred only at night and at the onset of freshes. Even though upstream movement had ceased for some two to four weeks, lampreys had not spawned and gonads remained far from mature by 30 November 1992.