Identifying Timing, Cues, Site Characteristics and Threats to Shortjaw kōkopu Spawning in Two Northland Streams

The shortjaw kōkopu ( Galaxias postvectis ) is the most threatened of New Zealand's diadromous galaxiids. Cryptic, nocturnal behaviours and their rarity mean ecological knowledge remains limited. Two sites in Northland (Waiotemarama Stream and Okawawa Stream) were monitored from March–July for 3 years to gather population data and information on spawning cues, timing, spawning site habitat and threats to spawning success. Fifteen shortjaw kōkopu spawning sites were identified throughout the study period above the wetted stream margins following spate flows in May–June. It is hypothesised that altered flow regimes, as a result of climate change, may impact spawning success through effects on spawning habitat, resource availability and the premature inundation of eggs. During monitoring, we identified the predation of eggs at multiple spawning sites by rats ( Rattus norvegicus , Rattus rattus ). A rodent control operation was established at two sites in an attempt to limit egg predation and increase the number of eggs reaching full development. Predator control results were variable, and a clear relationship between rat predation, rat control and spawning site outcomes was not identified. However, this study suggests the need for the consideration of pest management in the conservation of native freshwater fish in New Zealand.