Freshwater
Large adult inanga. Inanga is the most common whitebait species. Photo: Paul Franklin
How many (native fish) eggs
to make a whitebait fritter? It’s a lot more than you might think, as Dr Paul Franklin explains.
A
s whitebait season draws to a close, many hundreds of kilos of baby native fish have been hauled out of the lower reaches of our rivers and turned into that beloved New Zealand delicacy – whitebait fritters! We don’t know how much whitebait has been taken this year because it’s an unregulated fishery. Nor do we know how much the whitebait species can withstand the multitude of stressors (from habitat loss to harvesting) before there are significant ecological effects. What we do know is that many whitebait fritters have been eaten this year. The debate over the best recipes are never ending, and I don’t claim to know the best recipe, but I do hope to provide some insight into how many native fish eggs might go in to making a whitebait fritter.
Four out of the five whitebait species are threatened. Photo: Rob Suisted
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| Forest & Bird Te Reo o te Taiao
And the answer might just surprise you. Whitebait are the juveniles of five species of native galaxiid fish, returning to freshwater after spending the first few months of their lives at sea. This migration into freshwater is a critical part of their life-cycle, as they move upstream to the habitats where they will feed, grow into adults, mature, and then begin the cycle all over again. Understanding of the spawning biology of the whitebait species is relatively poor. However, all five have a somewhat unusual reproductive strategy that makes them uniquely susceptible to changes in river flows and bankside vegetation. In autumn and winter, all five species lay their eggs in habitats temporarily submerged by high water levels. For inanga (Galaxias maculatus, the most common whitebait species), which migrate downstream to estuaries to lay their eggs, this is high spring tides. For the other four species, banded kokopu (G. fasciatus), giant kokopu (G. argenteus), koaro (G. brevipinnis), and shortjaw kokopu (G. postvectis), this is high river flows caused by rainfall. The eggs of inanga are about 1mm in diameter and are typically laid within dense grasses that retain moisture and provide shading. These conditions help the eggs to survive out of water until they are ready to hatch about three to four weeks later. The eggs hatch when the spawning sites are reinundated by high river flows or, in the case of inanga, high spring tides. The larvae are then washed out to sea,