Movements and habitats of adult lamprey (Geotria australis) in two New Zealand waterways

The spring upstream spawning migration of the Southern Hemisphere lamprey, Geotria australis Gray, was investigated by monitoring movements of radio-tagged lampreys in two South Island, New Zealand, catchments of contrasting size (Okuti Stream, a small coastal stream and the Mataura River, a medium-sized lowland river). A total of 65 lampreys were radio-tagged and tracked by foot and helicopter between 1998 and 1999. Retention of the externally-mounted tags proved a problem, and lampreys were tracked for a maximum of 56 days. Most movement was recorded within a few days of release; movement was generally up stream although a number of fish also periodically moved down stream. Maximum daily movement in the Okuti Stream was 0.45 km compared with 12.6 km in the Mataura River; upstream movement was stimulated by increased flow but curtailed by large floods. During the day, lampreys were generally associated with bankside debris cover. The seven fish that moved furthest up the Mataura River all entered the same tributary, presumably in response to odours of their conspecifics. Thirteen lampreys retained for a year and released as nearly sexually mature, moved little from their place of liberation and possible reasons for this are discussed.