Locating whitebait spawning sites first step to salvation

Press, 11 July 1989, Page 21

Locating whitebait spawning sites first step to salvation

By

NICK HANCOX,

for the

Department of Conservation in ■ Hokitika —

MOST WHITEBAIT populations in New Zealand rivers have been depleted substantially. Most consumers may not stop to wonder where the delicacy comes from, but West Coast researchers have been studying the subject. Department of Conservation staff are being helped by the Ministry of Agriculture and Fisheries Freshwater Fisheries Centre in Christchurch. They have started to locate spawning grounds of Inanga, the most common of five species which comprise the whitebait catch. Alan Buckland, one of the researchers, says it will be easier to protect major spawning grounds when they are identified — and conditions needed for successful spawning are determined. Such research could help keep the Coast whitebait resource thriving. Although fisheries scientists have observed and described

Inanga in detail, says Mr Buckland, no-one has attempted a broad survey of their spawning grounds with the idea of protecting them. \;• During the two-year survey, spawning areas have been pinpointed on the Karamea, Buller, Hokitika, Waitaha, Wanganui'and Turnbull rivers. It could take up to 10 years to complete a detailed West Coast survey. So far, spawning areas have been found among exotic pasture lands. Little is known about where the fish spawned before European settlement. A knowledge of Inanga’s natural spawning places would be important in restoring them. Although scientists can now say what sort of habitat adult fish require and where they prefer to spawn, little is known

about ideal spawning conditions, or why whitebait numbers fluctuate so much from year to year. “Spawning areas can be very vulnerable •; to damage from drainage programmes, roading or rubbish; .'dumping,” says Mr Buckland. -Itun-off from alluvial mining sites might also cause problems. 'i “But if we.know exactly where the spawning grounds are, then we are in. a? good position to ensure that protective measures can be included in any development proposals.” Environmental conditions required for. whitebait spawning are very stringent. In late summer and autumn, adult Inanga swim downriver from wetlands and side creeks to spawn close to places where fresh and saltwater meet.

The fish will wait in the rivers for a spring tide, then spawn after the tide has peaked. Spawning is done in shallow water's at the edge of a river or creek. The male fish produce milt, which turns the water a milky white colour. Spawning takes place among matted, soft grasses and root systems along river -banks. ’ Inanga lay their eggs in that grass to keep them from drying out. The next incoming spring tide will hatch the eggs, flushing the minute larvae out to. sea. Larvae spend about six months at sea, returning as whitebait in the spring. Those that make it past a barrage of predators swim upstream to rivers and wetlands and will grow into adult fish about five centimetres long. They will spawn the following autumn. Alan Buckland says he is confident about gaining local support for the work: “No West Coaster wants to see the whitebait fishery go down the drain.”