BIVALVE BIOLOGY

Evening Post, Volume CXX, Issue 22, 25 July 1935, Page 25

BIVALVE BIOLOGY

THE POPULAR OYSTER

AND TASTY TOHEROAS

The habits of the oyster, and to a lesser extent those of the toheroa and

pipi, were presented in an entertaining and instructive light by Mr. A. E. Heffofd last night when he talked to members of the Wellington Philosophical Society on the subject of these bivalves and on some of the problems connected with shellfish in general. The oyster, he suggested, needed no introduction; they had been eaten since the Stone Age, and they had been written about in rather glowing terms since before the begininng of the Christian era. They had, too, been the object of artificial cultivation for at least 2000 years, and in the last 50 years especially had been the object of very extensive and intensive scientific research. "So, in spite of his natural predisposition to habits of quiet seclusion, the oyster," remarked Mr. HefTord, "has made quite a big splash in classical, literary, commercial, and scientific circles. The toheroa in comparison is a relatively unknown quantity—and quality—wasting his sweetness on the desert air of a few lqnely beaches in remote parts of New Zealand; which is a very good thing for the toheroas and for those responsible for their conservation." The occurrence in New Zealand of oysters almost identical with the common European oysters was briefly touched upon, and it was interesting to note that oysters are found in the hottest parts of the world, but not in the higher- latitudes. They cannot endure really cold climates. The oyster's anatomy and physiology and spawning habits were detailed by Mr. Hefford, and mention was made of its ability to change its sex from time to time. European and American oysters usually began by functioning as males when only a year old. A small proportion of these, about one in ten, changed over to females and produced eggs in the following spawning season, but the majority did not change until two years had passed. Females sometimes changed back to males and produced both eggs and sperms in the same year. Generally there was a tendency for the majority of young oysters to be males and for the majority of old oysters to be females. Other species, including the rock oyster, had been more recently found to be hermaphrodite, and it seemed quite possible that this habit of alternating sexes was general. OYSTER CULTIVATION. When speaking about the oyster's enemies and the problems connected With artificial cultivation, Mr. Hefford said that amongst Western nations the French had to be given pride of place as successful oyster cultivators. The main question was that of food for the larvae, this food consisting of very minute organisms. Projects for oyster farming in New Zealand had been formulated first in 1894. By 1898 most of them* had been recognised as failures or doomed to failure, and they were all abandoned by 1902. "It may be," said Mr. Hefford, "that even in those days of comparatively low wages the labour required to make artificial stocks of oysters a commercial success was too expensive to enable the producer to compete with the supplies from the existing natural beds, but it is also quite likely that the schemes when in actual operation presented practical 'difficulties that had not been anticipated. The same fate has met similar oyster cultivation schemes allover the world—unanticipated factors have i intervened, involving <^los 3 instead of profit—and that is why in the great centres of consumption there is still an unsatisfied demand for. oysters of good quality." Prospects in New Zealand, however, he thought, had become brighter than they were a few years ago. Interesting figures as regards the World's oyster trade revealed the fact that New Zealand oyster production has averaged about 38,000 three-bushel sacks annually. In 55 years England's oyster production has declined from 53,577,000 oysters in 1887 to 10,740,000 in 1932. French production, too, showed a decline, but the United States had shown a fairly constant figure. MILLIONS OF TOHEROAS. Although the genus to which the toheroa belonged was fairly widely distributed throughout the world, the species to which the toheroa belonged was apparently peculiar to New Zealand, Mr. Hefford went on to say. All the areas where toheroas occurred had, without exception, two characteristics. They are all firm, rather flat, sandy beaches where normally a heavy surf breaks. And in every case there is close proximity to fresh-water drainage, either in the form of seepage from lagoons situated on the landward side of the coastal dunes or else from numerous springs or small creeks. This, it was suggested, was due to the fact that in such localities an adequate food supply was ensured. "The officials of the fisheries branch of the Marine Department are primarily interested ili toheroas as a "sea product of importance as a foodstuff and as a commercial commodity. As a subject for intensive biological research it has to be left, like so many similar subjects, to non-departmental investigators or to the time when the necessary staff and facilities for such work will be provided by the State. We try to ensure that the toheroa is utilised rationally, and that supplies may be conserved for the benefit of posterity by getting, as a basis' for regulations, such information on the fundamental facts about their distribution and abundance as we can from the occasional opportunities for observation that present circumstances allow." Toheroas apparently tolerate overcrowding. Estimates of the toheroa population on the Ninety-mile Beach were not loss than 11A millions of toheroas over three inches in length spread over 30 miles of bench. The toheroa, added Mr. Hefford, In conclusion, grew at about the rate of one inch per , annum.