H.-15

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in a general way that our oyster reproduction shows considerable variation : it takes place more abundantly in some years than in others ; the summer season of 1927-28, for example, which was very warm and genial, was by far the best oyster-spawning season which has occurred between 1925 and 1930 ; the fixation of young oysters is also known to take place on a more generous scale on some beds than on others. Generally speaking, the oyster beds of shallow bays in which the water in summer warms up quickly, give better results than beds which are adjacent to deeper water. It is desirable, however, to have these phenomena recorded in terms of scientific precision. Otherwise oystercultivation and other operations cannot be organized so as to ensure the most profitable return for the output of labour and expenditure. There appear to be some oyster areas where successful spawning is the exception rather than the rule, and where the stock is maintained by the generation of one satisfactory brood in several years. When such beds are in their virgin condition this state of affairs is not easily recognized, and in fact has not been recognized. A concrete instance is the case of the oysters in the Coromandel district. These were once exceedingly well-stocked beds. In the past they were greatly overpicked and seriously depleted. To remedy this, considerable attention was paid to rock-wall cultivation when this kind of work was first taken in hand by the Department. It has, however, produced exceedingly little result, for the reason that the numerous artificial rock-walls were built in places where very little successful spatting has subsequently taken place. Similar rock-walls in the Bay of Islands, on the other hand, have produced oysters abundantly. The difference has undoubtedly been a matter of temperature, though other factors also may have operated to some extent; but the significance of this was not understood at the time when the work was undertaken, and the reason was that no scientific observations had been made. A more extreme case of wasted effort owing to the ignorance of this factor was when, in 1915, northern rock-oysters were transplanted to the Marlborough Sounds where they failed to reproduce, and the experiment proved a failure. In the past year, as mentioned above, we have found that oyster-reproduction has been generally successful in the Kaipara Harbour, but has practically failed in the Bay of Islands and in the Hauraki Gulf. In my report for last year some mention was made of the science of hydrography in connection with the visit of the Danish research steamer. I expressed the opinion that until a series of hydrographical investigations had been made for the elucidation of the physical and chemical character of the seas around New Zealand we should never obtain a complete understanding of the migrations and distribution of many of our important food fishes. The provision for such work still remains a hope for the future. In the meantime, an attempt has been made to gather together such records as exist as to temperature observations in New Zealand seas. By the courtesy of the Naval Secretary records of temperatures taken between 1921 and 1928 on H.M. ships " Chatham," " Diomede," and " Dunedin " have been collected and tabulated for further study and reference. Arrangements have also been made for the regular recording of sea-temperature by the New Zealand Government ship " Tutanekai "in the course of her periodical cruises to the lighthouses. In time we shall thus have more precise knowledge of this aspect of sea conditions, and we may be able to correlate the data with observed conditions with regard to the fisheries. It should also be mentioned that Captain Stewart, on his voyage with the whaling-fleets to the Antarctic in the 1929-30 summer, took daily observations of sea-water temperatures, &c. These records will serve to augment the records which have been made on various Antarctic expeditions. In this connection it may be observed that annual variations in the drift of cold water from the Antarctic must exert a profound influence upon the spawning and migration of fishes off the New Zealand coasts as well as upon the climatic conditions in the Dominion. It is at least possible that an abnormal drift of cold water from the Antarctic to these latitudes was responsible for the inclemency of the weather of last summer and also for the failure of oyster propagation and the delaying of the spawning of certain marine fishes off the east coast of New Zealand. Mussel Observations. Mussel-beds in Whangarei Harbour and in Tauranga Harbour have been inspected and roughly surveyed by the Marine Biologist in conection with the framing of regulations regarding their commercial exploitation. The survey of the mussel-beds in the Hauraki Gulf, which are of great extent and of considerable commercial value, is a task which still remains to be undertaken. A preliminary study of the growth-rate of these mussels has been made by Captain Daniel, Inspector of Fisheries, Auckland, by means of a marking experiment. The experimental cage was interfered with and came to grief, prematurely ending the experiment, but, so far as it went, it showed that the mussels increased in length by approximately 1 in. in a year. Snappek Investigations. The observations begun in 1925 have been continued by Captain Daniel as opportunity allowed. Catches have been measured and stomach contents have been examined with a view to showing the feeding habits of this species throughout the year. Salmon. Collections of scales from both quinnat and Atlantic salmon, for age-determination purposes, have been made by the co-operation of various outside helpers, but nothing in the nature of a comprehensive study of this material can be made until additions can be made to our staff and facilities for research.