Readers of the Transactions will be aware that valuable researches have, during recent years, been carried out by Prof. Malcolm, of Otago University, on the food value of certain New Zealand fishes, of oysters and other products.
Among the substances investigated is Mutton Bird oil. This oil has been found to be very rich in Vitamin “A”; in fact, it is stated by Malcolm (Trans., vol. 56, p. 658, 1926), that Mutton Bird oil is one of the richest natural sources of Vitamin “A.” It is proposed to discuss here not the importance and value of vitamines but the source of this oil.
The oil, as examined by Malcolm, was obtained from the crops of fledgling Mutton Birds (Aestrelata Lessoni). It is a remarkable fact that young birds, in the down, may contain in their crops so large a quantity as 100 to 120 cc. of oil. The number of Mutton Birds on the coast of New Zealand is enormous.
In the Otago Daily Times of November 24th, 1925, an account is given by the writer of a flight of Mutton Birds in which it was estimated that 216,000 birds passed a point on the coast in three hours. It is believed that the oil is fed to the young birds by their parents. The supply of this must obviously be very abundant.
Mutton Bird oil is characterised by the presence in it of cetyl alcohol. Numerous attempts have been made to discover the source of this oil: various fishes and other possible foods of the Mutton Bird have been examined but no oil containing cetyl alcohol has been discovered.
Being asked by Dr. Malcolm on April 2nd, 1927, to be present at the examination of some Mutton Birds I suggested the possibility of pelagic cephalopods being an important source of food for the Mutton Birds and hence a possible source of the oil. It had been shown by Sir James Hector, many years ago, that these organisms form an important part of the diet of the ocean-ranging Diomedeae.
The oil of the young Mutton Bird examined with Dr. Malcolm was found to contain a large number of glistening scales which at first suggested suspended particles of mica, but examination with the microscope showed them to be pigmented cells such as are commonly found in the cutis of mollusca.
Proceeding to the examination of the contents of the gizzard for beaks of cephalopods and other resistant debris it was immediately
apparent that beaks of small cephalopods were present in large numbers.
A portion of one of these is shown in the accompanying photograph (Fig. 1). The beaks were packed with striped muscular fibres: these may represent the food of the cephalopod; or they may have been packed into position by the action of the gizzard, since free muscle fibres were abundant in the gizzard contents.
In addition to the beaks, above described, there were numerous spherical lenses and parts of lenses of the eye of some animal.
The largest of these, which resembled fish lenses, were 2.5 mm. in diameter, the smallest were mere bead-like remains of an amber colour.
A group of these lens remains is shown in Fig. 2.
On dissection these lenses were found to be composed of serrated fibres with closely-fitting inter-digitations. (See photo-micrograph Fig. 3).
The question arose:—Are these lenses derived from the eye of the cephalopod or from some other animal such as a small fish?
Professor Benham very kindly supplied me with the lens of a squid (Ommastrephes sloani). This on examination showed an entirely different structure, viz., laminated plates with sinuous—not serrated—borders.
We have therefore in the gizzard of the Mutton Bird two possible sources of the Mutton Bird oil, viz:—
(a) the cephalopod,
(b) the fish or other animal on which the cephalopod feeds.
The beaks found measured up to 7 mm. in length; they must therefore have belonged to a small cephalopod, either a young animal or a small species. Several small species of cephalopod are known in the neighbourhood of N.Z. e.g. Pinnoctopus cordiformis, described by Quoy and Gain (Encycl. Brit.) and others from the Kermadec Islands, described by Berry (see Trans. N.Z. Inst., vol. 46, p. 134, et seq., 1913). The former is 8 to 9 inches long; the latter vary from 90 to 120 mm. Some of the latter are littoral forms and others deep-sea forms but there may be pelagic forms yet to be discovered.
The next step in the enquiry will be to obtain some of these pelagic cephalopods, to compare their beaks with those found in the Mutton Bird, to examine their tissues for cetyl alcohol and their stomach contents for the remains of fish.
It is hoped that this note may stimulate those who have the facilities and the opportunities to follow up the enquiry.
Note: The optic lens of the fish is composed of serrated fibres and the muscle fibres of the fish are of the striated variety.