WAYS OF THE WILD.

Auckland Star, Volume LIX, Issue 77, 31 March 1928, Page 1 (Supplement)

WAYS OF THE WILD.

A NATURALIST'S NOTEBOOK. MAKO AND WHITE SHARK,

(By A. T. PYCROFT.)

The Mako or Isurus glaucus. belongs to the genus of mackerel >hark~. Ilii.species reaches a length of from twenty to twenty-five feet; it is strong, swift, and voracious. In recent rears it b.ibeen frequently taken oil the rod on parts of the east coat-t of the North Island. It also range* from Hawai and Japan westward to the Hed Sc*. Certain of the teeth were formerly inucli prized by the Maoris as car ornaments. There is only one published acconnt of the occurrence of the Porbeagle la num. nasus on New Zealand coasts. It i* known for its murderous voracity; the teeth are long and lanceolate. with sharp lateral edges and two ba»al cusps. At one time teeth of the porbeagle were brought from An-t ra 1 1:.. where the species is common, for tinpurpose of trading them with the Maoris as those of the Mako, which ire similar, but lack the cusj>.~. TinMaoris, however, saw they were not identical, and they were not appreciated. The colour of the shark is dark >latcy !jrey on the back, merging into black

an the edges of the tins, while underneath. The great While thark belongto the s&tue family as the Mako. The

species is known as Carcliarodon careharias; it is rarely taken on the NewZealand eoasts. but is found in all tropical seas of the world. It i> one of the largest and most formidable of all sharks, and reaches a length of thirty feet. The finely serrated teeth of this species were also highly prized as ornaments bv the Maoris.

This completes a short description <>f all recorded species of sharks found in New Zealand waters. Phosphates and Fossilised Shark's Teeth.

Mr. W. E. Watkins, of Otahuhu. is interested in the discovery of fossilised shark's teeth found in Moroccan phosphate and desires to know what kind of shark's teeth they are. and what iknown about phosphate, now co largcly used as a fertiliser. The phosphate referred to was brought from Morocco by the s.s. Indianola. It was loaded at Casa Blanca on the West African coast, being brought to that port, from the workings situated about one hundred and fifty miles inland. Phosphate rock is a sedimentary deposit which occurs is a hard rock interstratined with beds of sandstone, shale, or other sediments. Phosphate deposits of the North African beds are of this tyj>e. A lame percentage of Moroccan phosphate is obtained in powder form and the rest i* luite friable. This field ha> been a factor in the world's production of phosphate rock since 1921. when 3."!.0(tn tons were produced, while in iy 225,000 tons were produced. Another type of deposit commonly classed as phosphate rock is the porou?oraline, or other limestone, of tropical islands which has been permeated with phosphata leached from guano. Chrbtmas Island in the Indian Ocean, and Nauru and Ocean Islands in the Pacific, near the equator, arc examples. The phosphate deposits of these three islands are among the richest of the world's supply. Leached Tuano deposits are also found in the West Indian Islands. Two of these

islands, Christmas and Ocean, have Inn;' been a part of the British Enipir«T. The other, Nauru, belonged to Germany until November, 1914, when it was seized by the British Navy and assijrned permanently to the British at the Peace Conference by the Nauru Islands Agreement Act of 1919. The phosphate was to be divided between England, Australia and New Zealand in the ratio of 47, 47 and 16 per cent respectively. One of the notable features of the last two or three decades is the steady increase in the world's population. Huge Deposits.

On account of a diminution in virgin soil fertility throughout the world the human race is using up the available phosphate supply at an increasing raJ«*. Fortunately the discovery and opening up of new deposits have so far helped to keep paee with the increased demand, so that there does not seem to be any danger for some time to come of phosphate shortage threatening the agricultural world. In 1907 the total output of phosphate rock for the world wa» 4,780,000 tons. The United States supplied practically half. In 191;; tb<total output for the world was 7,230.000 tons, the United Stales again contributing approximately fifty per cent of this amount.

There are said to be no less tlian 100,000,000 tons of phosphate on Nauru and Ocean islands. How these extensive and wonderfully rich deposits came into existence has been the subject of much conjecture. What is known asthe "Bird" theory is the most popular and generally accepted.

The original guano, in the form of bird excreta, must have been deposited many thousands of years ago. There is evidence that the islands have been submerged on several occasions. The result is that all impurities have long since been washed away and practically "odlv the pure phosphate of lime remains. Nauru phosphate contains nearly eightvsix per cent of tricalcic pbosphaf« of lime. The birds believed to be responsible for these deposits are now* extinct, and the islands to-day are rarely if ever visited by birds.

Fossilised Teeth. The finding of fossilised shark's tmh in the Moroccan phosphate show? thai these deposits have been submerged and during the period of submergence sharks, which are cartilagenous fish and were among the first fish to appear in the seas, left us as evidence of th'-ir existence at that time only their teei ii and fin spines. The tee'th shown t.> me appear to be identical with those <.f the Porbeagle, having two basal m-pi-. The teeth are those of members 01 1 h.family Lamnidae. Members of tlis family are the swiftest, stronp. -t. a T,d most voracious of all sharks. Teeth i f members of the Lamnoid families ar« especially numerous as fossils. TbHr teeth abound in all suitable i.«ek deposits from Mesozoic times till u<jw. A most primitive form is the com von sand shark of the Atlantic Coa-t, v liirh has similar teeth. There is silso a similar form in the Mediterranean. A do>cly allied family are the Goblin sharks, found in the Kuro Shiwo. warm "Black Current,"' or Gulf Stream of Jajiart. These are characterised by the development of the snout into a lonj; fiat blade extending far beyond the month. Another variety is a very remarkable survival of a very ancient form. It is a a interesting fart that the centre c-f abundance of these relic* of ancient Bfg is in tin "«■* Current of Japan.