First observations of spawning nests in the pouched lamprey (Geotria australis)

Abstract

The pouched lamprey (Geotria australis), one of four Southern Hemisphere lamprey species, is New Zealand’s only freshwater representative of the agnathans. In contrast to that of Northern Hemisphere lampreys, the reproductive ecology of Southern Hemisphere lampreys is poorly understood, with no documented nesting sites or spawning behaviours. In the present study, we utilized passive integrated transponder tags to track migratory adult G. australis to locate spawning sites. Across 2 years, six cryptic nesting sites were discovered, each containing eggs and a single male and female lamprey. The postspawning pairs were all located underneath large boulders, with the eggs forming a coagulated cluster that adhered to the underside of the boulder. Both the male and female lamprey survived spawning for over 105 days. The observed spawning nests highlight a substantial divergence in the reproductive behaviour between Northern and Southern Hemisphere lampreys, as the present observations of G. australis are the first that support clustered cryptic egg deposition and an extended time to mortality postspawning. This study offers the first insights to the long-standing mystery of Southern Hemisphere lamprey reproduction.