Downstream Spawning Migration in the New Zealand Torrentfish: A Mechanism to Enhance Transport of Larvae to Marine Pelagic Rearing Habitats
Our extensive sampling around the South Island of New Zealand confirms that primarily female torrentfish undertake extensive upstream migrations (>100 km), with most males remaining in downstream river reaches. Downstream migration by females to spawning sites in riffles close to the sea occurs from late spring. This pattern of upstream migration during growth to maturity, followed by downstream migration to near-marine spawning habitat is a pattern that is repeated in a number of amphidromous fish species, particularly in species that either penetrate long distances inland or inhabit low gradient terrain. This pattern of migration also has close parallels with migrations in various catadromous fish species – rather than spawning in freshwater, the downstream spawning migration continues into near-shore marine habitats. We discuss possible functions for these downstream migrations and the apparent similarities between amphidromous and catadromous life histories in various Indo-Pacific fish species.