NATURE NOTES

New Zealand Herald, Volume LXXIII, Issue 22320, 18 January 1936, Page 1 (Supplement)

NATURE NOTES

BY It. A. FALLA

WARM WATER FISH

It was customary in the days of sailing ships to describe the pleasant climatic conditions in sub-tropical seas as "flving-fish weather." In a vessel from New Zealand homeward bound by way of Cape Horn the first flying fish seen in the South Atlantic Ocean was a sign that cold and stormy weather was at last a thing of the past, at least for some weeks. The association of the flying fishes with warmer seas represents correctly the distribution of that interesting family; it is determined strictly by a certain minimum temperature of the sea. This means that their distribution may be extended somewhat from the tropics during the summer season in both hemispheres, and their extended range will be represented by the isotherm of that minimum temperature—that is, the imaginary line showing the limits of water of that temperature at any time of year. In the South Pacific Ocean a few flying fish of the hardier species reach New Zealand seas in mid-summer and are to be seen commonly olf the north-east coast and in the Bay of Plenty. They are familiar to yachtsmen, deep-sea fishermen and campers near the ocean beaches; in fact, one of the best flight displays I have seen from one of these fish was inside the Tauranga Harbour. I have been looking up some notes of observations of flying fish made on this occasion and also during a spring voyage across the South Indian Ocean, prompted by the fact that Dr. E. L. Gill, of the Capetown Museum, has recently written to the journal Nature on the subject. Dr. Gill summarises what seem to him the most obvious facts about their flight. He considers that the motive power is the same in the air as in the sea: it is that of the tail shaft musculature exerted through the tail against the water. The flight is usually started by a swift rush at a low angle up to and through the surface, liut if this fails, for example, through jostling in a crowd, the fish is easily able to make a "standing start" from the surface itself; a quivering vibration of the tail launches it almost instantaneously into full flight. The same manoeuvre is regularly used to prolong the flight. At the end of the initial skim the fish often dives abruptly, but almost as often it dips the lower blade of the tail into the water instead and drives itself on for another stage. This may be repeated up to five or six times. It is surprising to see how short is the duration of the quivering dip and what vigorous fresh impulse is derived from it.

Dr. Gill considers that the impulse is derived entirely from the caudal fin or tail. The wide pectoral fins during the flight are stiffly spread; they are used with great skill as planes, but never as wings. He also expresses an opinion that the flight is not a blind rush; while its way lasts the fish can steer and turn up and down the waves and along them as gracefully as a petrel. This observation is possibly correct, but it has been questioned by other observers. For evidence of actual, "steering" it would be necessary to eliminate all possibility that changes of course might be due to wind and up-draughts from the surface of the sea. The fish mentioned above as observed at Tauranga rose from a "standing start" in Pilot Bay and flew on a curving course toward the entrance to the harbour, but this direction may well have been due to wind sweeping round the foot of Mount Maunganui.

In another observation, also, Dr. Gill is slightly at variance with other observers. He states that the usual end of a flight is a sudden dive with closed wings, but that sometimes the dive is preceded by a sailing action with slightly up-tilted body and planes, like a seagull gliding to rest on the sea. This second method is the more common in my observations of flying fish and the dive head-first is rare. In fact, the comparison of a seaplane alighting with the roar of the floats touching the water first is exactly the habit of most of the flying fish seen in New Zealand waters. It must be remembered, however, that there are many diiferent species of flying fish and conceded that both methods may be used.

The origin of the power of flight is thought to be the habit seen in some other fishes of "skittering" along the surface when escaping from their pursuers in the water. It is probably a means of securing safety, also, in the flying fishes. The most important modification of the body structure making it possible is the elongation and strengthening of the lower lobe of the caudal fin or tail. The spreading pectoral fins appear to have only secondary value, for they are even * better developed in the so-called "flyinggurnard," which does not fly so well as the true flying fish. As Dr. Gill remarks, the real mystery is not that the flying fish can fly, but that one small group* should have acquired a fin and tail structure adapted to flight and a singular adroitness in using it. The scientific study of the group has a long way to go before this mystery can be solved.

An able biologist, Dr. A. f. Bruun, of Denmark, has begun well with a review of the flying fishes of tho Atlantic, published last year. In it he detects the presence of two groups with different habits, one more primitive in structure and inhabiting coastal waters, the other more oceanic. Dr. Bruun visited New Zealand in 1028 during tho voyage of the Danish Research Ship Dana, and we may look forward to the publication of some of his observations in the Pacific at an early date.

A fish of very different appearance and habits from the flying fish was described to me some time ago in a letter from the Tuparoa Native School, lUiatoria. From an excellent sketch by Turei Grace it is recognisable as a porcupine fish, a sluggish species protected by an effective coat of armour. The spikes with which its body is entirely covered are modified scales built into a rigid interlocking system and part of the fish's external anatomy. As if this were not enough to deter a possible enemy the porcupine fish can puff itself up like a balloon by swallowing water, and when taken out of the water it achieves the same result by swallowing air. They are comparatively common in the warmer parts of New Zealand seas.

A valuable study of the life history of tho sea lion of the Falkland Islands has recently been completed by Mr. «T. E. Hamilton, of the Discovery Investigations staff. The method of research should be adopted in the case of all wild creatures that are likely to be exploited commercially. Mr. Hamilton concludes that adult males are the only class that can be reduced without damage to the herd and that such reduction must be within the rate of natural increase, which must be first determined by investigation.