Whitebait enigma

Forest and Bird, Issue 280, 1 May 1996, Page 46

Whitebait enigma

Ann Graeme

HITEBAITING that symbol of New Zealand life. Can there be any pastime that so exquisitely combines high excitement and dreamy boredom? It’s all about the little, silvery fish streaming into the net, into the bucket, and into the frypan. But those tiny fish have a story to tell far beyond the wildest dreams of the whitebaiter. The whitebait that escape the nets swim on up river. They are not a single species, but the young of five native freshwater fish — inanga, koaro, and three species of kokopu. These fish all belong to the southern hemisphere family Galaxiidae. Kokopu are found only in New Zealand while koaro are also found in southeastern Australia. Inanga, occurring also in Australia and South America, are one of the most widely distributed freshwater fish in the world. Galaxiids get their name from the profusion of spots on the first species described, which were fancied to resemble that galaxy of stars we call the Milky Way. By far the most numerous among the whitebait are the young inanga, swimming upstream to grow into adulthood in rivers, lakes and swamps. Inanga cannot climb even small falls or long rapids, so they do not venture far inland. Neither does the shy, nocturnal giant kokopu

whose young seek swamps and creeks overhung with flax and raupo, tree-lined banks and sunken logs where they can skulk and hide during the day. On the other hand, the young of the koaro, the banded kokopu and the rare shortjawed kokopu are agile climbers, scaling vertical rock faces and turbulent falls to reach small creeks sometimes far inland. They can only live in undisturbed streams edged with native forest or shrubland (or tussock, for the koaro), and their populations reflect their diminished habitat. Mystery still surrounds the lives of these secretive native fish. Recent studies have revealed the extraordinary breeding habits of the banded kokopu which in heavy rain leave the stream to spawn in the forest litter. Their eggs lie dormant until the next rain, when they hatch and the tiny fish wriggle through the leaves back into the stream. Best-studied of the galaxiids is the inanga — for the obvious reason that their young make up most of the whitebait we eat. In autumn, sensing the coming of the full or new moon, adult inanga migrate downstream into estuaries. They congregate in the salt marshes or along the grassy riverbanks, awaiting the high tides associated with the lunar cycle. The tide floods over the banks. Almost high and dry, the fish writhe and wriggle in the grasses and rushes, laying their eggs deep

among the grass stems and casting their sperm (known as milt) over them. The tide falls. The adult fish die but their fertilised eggs remain, out of water but kept damp in the base of the grasses. Two weeks or four weeks later when the high tide reaches them again, the eggs hatch and the tiny fish drift out to sea on the falling tide. They join the young of the other whitebait species that have been swept from their spawning places further upstream. Drifting for months in the plankton, eating (or being eaten) and growing, the young fish eventually return to shore in spring to crowd into shoals and swim upstream like their parents before them. Those nourished in the harbours or estuaries return upstream in greater numbers than those swept off-shore by the ocean currents to an uncertain future. It follows that those rivers providing upstream, forested habitat and estuarine wetland nurseries, continue to support the largest whitebait populations. Nowadays whitebait schools are only a shadow of the enormous shoals which used to swim up our rivers. The whitebait nets take their toll, but it is the loss of native forest cover which has decimated koaro, shortjawed and banded kokopu. And it is the draining and clearing of lowland swamps and creeks which has been the biggest cause in the decline of inanga and giant kokopu. Less than one percent of Canterbury’s original wetlands remain, for example, two percent

in the Bay of Plenty and eight percent in the Waikato. Trout — an introduced fish — eat whitebait and artificial barriers block whitebait migrations. While hydro dams largely bar the movement of eels, it is the seemingly inoffensive culverts and dams and fords of roadmakers, farmers and foresters that have spelt death to many small populations of native fish. With simple modifications these structures could be made surmountable and fish-friendly. Just like many native birds, New Zealand’s little-known freshwater fish are threatened. Thoughtful planning by local bodies and landowners can easily accommodate the needs of these fishes, species Just as native, just as iconic and just as worthy of protection as our birds and forests. Spare a thought for the whitebait. They are the children of old New Zealand, of species so closely adapted to their environment that they undertake migrations beyond the wit of humans to fully understand. Perhaps we should think

beyond the frypan?

ANN GRAEME 1s. the | national coordinator of — Forest and Bird’s Kiwi | Conservation Club. |

Actions to help native fish

» Protect and restore riverside vegetation. » Protect spawning areas at river mouths. » Ensure all dams, culverts and other obstacles in waterways are built to allow fish passage.

» Tighten controls on whitebaiting. > Refrain from introducing trout to waterways where they have not yet been liberated. » Give native fish priority over introduced fish in managing waterways.