THE LIFE OF THE WHITEBAIT

Hokitika Guardian, 22 October 1930, Page 7

THE LIFE OF THE WHITEBAIT

SPAWN IN CRASS. m __ \ t - NEW LIGHT ON PUZZLE. The investigations being carried on at present by the Marine Department into the life' history of the whitebait attenuatus) are proving most fruitful, and when the complete text of the results obtained by Captain L. Hayes, which will form the subject of a treatise to be published in the Transaction of the New Zealand Institute, are published, the public will realise that so much that is new has been discovered in regard to whitebait that many conceptions of its habits have been proved erroneous states the “Post.” When it is realised that the adult whitebait (the common minnow, or inanga) spawn at the limit of highwater mark amongst the grass in about an inch and a half of water, the eggs remaining fertile provided there is sufficient evaporation from the soil to keep them moist, for periods ranging to as many as fifty days and that this spawning is done within a few miles of the mouths of New Zealand rivers, the damage caused by the grazing of these lands by heavy-foot-ed stock may be readily assessed. In a piece of turf some seven inches in diameter—the sine of a draught horse footprint—6o6o whitebait were recovered by artificial hatching, the unfertile eggs proving a very small fraction of the whole. The report of the Marine Department to the Government says, under scientific investigations”:—“Until the gaps in our knowledge of the life history of this species could be filled up we were not in a position to tackle ;the framing of regulations for its conservation with due insight into the fundamental facts of the situation. In particular it was recognised that light should be thrown on the spawning of the species. Besides the well-known fact that whitebait, which are inanga, at a juvenile stage, enter the mouths of rivers from the sea, there existed convincing evidence that the adults when about to spawn migrated in shoals from fresh water down to tidal water. The Maoris believed that the, inanga spawned in the sea, and this view has been accepted by European and New Zealand writers on the subject.

SPAWNING MYSTERY SOLVED

• “The exact location and identification of the naturally deposited spawn and the distribution of the larval (pre -whitebait) stages were unknown until (the Department’s investigations were made. Sbme preliminary light was thrown on the subject when, in May 1929, ripe inanga of both sexes were obtained from the Whaknpuni drain, ' Siear Foxton, and the ova artifically fertilised by Cnptain L. Hayes. Different lots of these ova were kept dur-

ingfetEe incubation stage in water of i'ou’iUdffferent grades of salinity—(l) Sea-water from Wellington harbour, (2) a r mixture of two parts of sea-wat-or’aSiif one part of fresh water, (3) a mixture of one part sea-water and two parts’fresh water, (4) fresh Wellington tap water (dervided from the Wainuiomata). “The somewhat surprising outcome of this was that healthy larval fishes hatched out from each lot, indicating that both eggs (embryos) and larvae w’ere tolerant to either fresh, brackish or salt water, which is in itself a very exceptional phenomenon. It suggested* that' the natural incubation of this species ’tools place under very variable cofiditiOns with regard to the salinity of tiie surrounding water, such as would be found, for instance, near the mouth of a tidal river. it was also found that the eggs preserved their vitality, when kept -packed in damp moss .for several days. By this experiment -also the character of the egg and ;of the newlv-hatched larva was determined —a necessary startingpoint for the identification of the same when found naturally occurring. The number of eggs produced by a single female inanga has beeen found to.-vary from 1500 in the smallest (2fin) fish to over 13,000 in a very large (o£in) specimen.

A .HIGH TRADE ROMANCE “A further step now-, to lie recorded is the actual observation of the act of spawning, the location of the spawn, the s incubation period, the emergence of the newly-hatched young fish, and their natural distribution. These observations were carried out by Captain Hayes on tfie Mannwatu River between about three and a half and eight miles from its mouth, on a visit made amout the middle of March, 1930, and v6b:-shb.fejuent visits. The main facts which he brought to light are as follows: The ripe fish migrate to the tidal water in shoals, arriving at the time of -spring tides. These migrations were observed to take place in the Manawatu River- this year in March (once), April (twice), and May (twice). There was evidence to support the supposition that a spawning had also taken place in February. For spawning the shoal approached the - yery, margin of the river at the time of-high' water. The minute eggs are deposited among rushes, grass, or other vegetation which affords conceal ment for the spawning fishes and cover for the eggs, which adhere in masses on the ground about the base of the stems of rushes or grasses. Spawning did not take place till the highest of the spring tides had passed.

“The ova were thus left ‘high and dry’ when the tide receded, and since they were deposited as near the water’s edge as ihe fish could get, and the tides which followed were of diminishing height, there could he no further cohtact with the water until the next spring tides occurred. The spawn is thus assured complete protection from any aquatic enemy for practically the whole of the incubation period. When the eggs are once more submerged on the next spring tidq\reaching them, hatching takes

place and the larvae are carried down by the ebb tide. At the time when the eggs were hatching out considerable quantities of the larvae were taken by tow-netting in tile estuary just above the bar. ' It lias been demonstrated that if the spring tides succeeding the one on which spawning took place are not so high, and therefore do not reach the zone where the spawn is deposited, the embryos remain unharmed while hatching is deferred. •AN UNGUARDED DANGER “The period between spawning and batching may thus be about fourteen days, or it may lie extended to as much as forty-eight days. This provision by which the parent fish deposit their spawn at places which are only covered with water at the highest tides practically ensured immunity from enemies under the original natural conditions which held previous to the colonisation of New Zealand. Under present-day conditions, however, adverse factors come into play which were not contemplated, so to speak, in the original natural state of affairs. In the locality investigated it was found that horses, cattle and even human beings, by trampling over the ground on which the whitebait eggs were deposited in hundreds o'f thousands, wrought a considerable amount of destruction. A full account of these observations and other points connected with the natural history of the whitebait will appear in a later report.”