Spawning, egg development and recruitment of diadromous galaxiids in Taranaki, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University

Abstract

Spawning biology of Galaxias postvectis Clarke (shortjaw kokopu) was investigated in streams in northwest Taranaki, New Zealand. Most G. postvectis were found to spawn near their adult habitat on the river bank during spate flows between May 9 and 17, 2001. Other galaxiids captured appeared to begin spawning earlier in late April. Sixteen galaxiid nests were discovered amongst flooded areas, lying on or amongst the substrate, vegetation and debris on the banks of the Katikara Stream. Mitochondrial (mt) DNA sequences were used to identify these morphologically similar eggs, with 12 being identified as G. postvectis and four as G. fasciatus Gray (banded kokopu). Galaxias fasciatus nest sites had more vegetation and debris than G. postvectis nests. The presence of a backwater or pool, cover and gravel were found to be important characteristics associated with both species nests. Egg development took around three to four weeks on the Katikara Stream margins. Under experimental conditions, most G. postvectis and G. fasciatus eggs were found to hatch within the first hour of re-immersion in water, and more hatching occurred in moving than still water at warmer temperatures. In the Katikara Stream, eggs hatched and moved downstream only at times of increased water levels. MtDNA sequences were used to identify G. fasciatus, G. postvectis and G. brevipinnis Günther (koaro) larvae caught drifting downstream in May and June, 2001. From reproductive assessment of adults captured, developmental stage of eggs in nests found, and timing of emigrating larvae, G. fasciatus appeared to spawn earlier than G. brevipinnis, and both species spawned earlier than G. postvectis. Whitebait migrations were examined within the tidal influence and c. 40 km inland in two rivers in south Taranaki, one with a dam and one without. Whitebait catches were dominated by G. maculatus (Jenyns) (inanga) and catches appeared to be similar in both rivers. Large schools of whitebait were however seen below the Patea Dam from October onwards in the Patea River. No whitebait were found to surmount the dam using the elver pass. So the presence of a dam does not appear to affect whitebait recruitment within the tidal influence, however it does block whitebait migrating further upstream to adult habitat.