Barry Bennett, of Halfway Bush, asks :-
Where do whitebait go, and why, in the off-season?
The late Bob McDowall, a fisheries biologist with the National Institute of Water and Air and author of "The New Zealand Whitebait Book" which unfortunately is out of print, responded.
To the whitebait there is no "off-season", just other times in their lifecycle, part of which is spent in fresh water and part in sea water.
Basically, inanga, the most important species in the catch, are an annual species who live just over a year. The adult is about 7-10cm long and lives in bush-covered streams and swamps.
In late autumn the mature inanga migrate downstream to the lower river or estuaries to spawn in grasses covered by water at high (spring) tides. After spawning the adults die.
The eggs remain in the grasses until the next spring tide covers them at which time the young hatch and the laval fish are washed out to sea. Their first winter is spent feeding at sea.
In late winter/early spring the juvenile fish migrate back up rivers and streams (the "run"). First they have to locate a river or stream whilst at sea. The start of the "run" is thought to be related to river flows (ie shortly after floods) and perhaps the phases of the moon (ie incoming spring tides which makes travel against the river flow easier).
Over summer, amongst sheltering vegetation in the upper reaches of streams or in swamps, they grow into adults before starting the cycle all over again.
But we are aware of their existence mainly at the time they shoal at sea and run up rivers. The most visible distant sign is the circling seabirds who feed on the little fish who are feeding on the whitebait, plus of course the appearence of nets, whitebaiters and fish-shop signs during the brief running season.