PHOSPHORESCENT FISH

Waikato Times, Volume 108, Issue 18076, 21 July 1930, Page 3

PHOSPHORESCENT FISH

THE STUDY OF PLANKTON. HAUNT OF SEALS AND WHALES. THRILLING CHASE BY •‘KILLERS.” (By Professor T. Harvey Jehnston.) (All rights reserved). Whales constitute a very Important part of the sub-Antarctic and Antarctic marine fauna and were especially looked for during the voyage of the Discovery in the Mawson Expedition. Whaling is undertaken from eertain bays in Kerguelen as headquarters, the chief whales taken being the blue, the dinner, and the humpback, ( the last being captured in the early part of the season and the first named constituting the most important of the three. . We saw a few finners x and killers and a number of pike whales before entering the pack-ice. The lastnamed became very abundant in the pack-ice and at this time the huge blue whale—the largest member of the animal kingdom—began to make its appearance. Its’ occurrence was sporadic, though in some localities, such as near Enderby Land, they were very abundant, especially along the edge of the close pack-ice and in the larger leads in the pack. As is wellknown, the prevalence of Blue whales in any locality depends on the abundance of the particular kind of crustacean,” kril on which it feeds. Other cetaceans seen occasionally during the voyage were various dolphins, blackfish and sperm whale. On one occasion, three killers were seen pursuing a crab-eating seal which they captured just before the latter was able to reach the safety of an ice doe. The major part of the biological work of the Experition was concerned willi plankton—that great body of organisms which drift or swim more or less feebly in the superficial as well as the deeper waters. of the ocean. It is not always easy to draw; a line of demarcation between plankton and nekton, a term used to include actively swimming organisms such as fish and cuttlefish which have a much greater individual range of movement and are not so restricted to a parti- j cular environment. The remainder j of marine life may be classed as ben- 1 thos, a term comprising fixed, sedentary or slowly moving - organisms associated with the sea floor or living between tide marks; sponges, starfish and most molluses and worms falling under this category.

Sea Animals Food Supply. It. is from the plankton that the majority, of animals in the sea ultimately derive their supply of food — hence the importance of its study. It consists' largely of microscopic plants called diatoms, and of small . crustaceans together with pelagic molluscs (pteropods), various kinds of worms and jelly fish, the larvae of fish and invertebrates, and lowly animals belonging to the protozoa, such as radiolaria and foraminifera. As many of these organisms have skeletons of silica or of lime, there becomes built upon the ocean floor, as a result of the death of these small creatures, an ooze, classified accordingly to its main constituent and varying according to depili and locality. Diatom ooze predominates on'the Antarctic sea floor, the diatoms occurring in enormous numbers in the more superficial portions of Antarctic and sub-Antarctic waters, imparting to them a peculiar greenish appearance markedly different from the deep blue oolour of water of similar depth, but containing relatively few-of these siliceous plants. • As this surface layer becomes frozen, it is usual to find a broad yellowish or greenish band in the pack-ice, the colour being due lo these included diatom§. Since diatoms are able to build up living material from inorganic matter in the ocean and to store up energy derived from the sun’s rays, they,*,together with other- microscopic pelagic plants (phytoplankton), form the great source of food supply from which animal life derives its nourishment, directly or indirectly. Hence abundance of phytoplankton is correlated with abundance of planktonic animal life, ranging from microscopic species to those measuring an inch or more in length, e.g., kril. Of course there are much larger organisms in the plankton—such as medusae, certain worms, eto., but they probably play a minor role as sources of food supply for other organisms. "• l' The study of plankton Is oarried on quantitatively as well as qualitatively; in other words, one desires to know not only what kinds of plants and animals constitute it in any particular locality or. depth of ooean, hut also what bulk of eaoh of the Important types occurs in a known quantity of water. Hence a standardised method of collecting has been adopted. Series of nets eaoh of a particular diameter and mesh are lowered Into the water for a known distance and hauled, up again at a known rate. In some cases a device is attached so that the net j is made to-close on its way up when! it reaches a definite distance from the surface. Thus one learns what kinds 'and numbers of organisms oocur in a certain volume of water between certain depths. Other nets are towed obliquely behind the ship for a known distance at a known speed so that a kind of cross section of the life of the more superficial waters is obtained.

Like Liners With Lighted Portholes. For larger organisms a net with a much greater diameter and a wider mesh was used, more especially for the capture of such as lived at much greater depths. Though small pelagic fish were taken on many occasions in the finer nets, especially from the deeper levels, it was the large net which led to the capture of most of the fish as well as larger • nedusae, such as atolla, crustacea, cuttlefish, etc., some of these animals being transparent and others brightly coloured. The “phosphorescent” fish were very striking on account of the arrangement of the luminous organs or photophores. One author has likened them to miniature ocean liners with all portholes brilliantly lighted and standing in marked contrast with the surrounding darkness. Practicallyj all these deep sea fish came up ! damaged, partly through the great | diminution of pressure and partly through their activities in endeavouring to -escape from the net or from the strong metal bucket in which the net terminates. ■. The nature of the beach at Possession and Heard Islands was such that no shore dwelling organisms were obtained, though specimens cast up by heavy weather were collected. At Hoyal Sound, Kerguelen, conditions 1 were quite different, on account of the fiord-like bays and sheltered coves, and permitted good collections to be made between tide marks. The abundance of small fish, or several species,

living under stonps near low spring tide njark is. rathef striking, the same species occurring also in defeper water among the kelp. Some of these fish have a very wide distribution in the sub-Antarctic regions, having been reported from similar situations “at Tierra del Fuego, Falklands, South Georgia and Macquarie Islands, one of them extending to Graham’s Land in Antarctica. The great development of mussel banks is quite a feature of some parts of the Sound, while empty shels of these . molluscs, together with of limpets thrown ashore along with the kelp on which they live, occur in great quantity scattered over the lower parts of the landscape, indicating the extent to which these creatures had been utilised as food by birds, the black-back-ed gull especially. In order to collect organisms from deeper waters dredging was resorted J to, various kinds of dredges being j utilised according-to the depth. A] fine collection of specimens has been j obtained as a result of this work and will be distributed later on to specialists in various parts of the world for investigation and report. The Albatross Diot. Throughout the cruise, when time permitted, an examination of the various vertebrates collected—fish, i

birds and mammals—was made with a view tb ascertaining the nature of their food as revealed by their stomach contents, and at the same time any parasites occurring on the surface of these animals or in their digestive tracts were added to the collections. The fish were found to feed on other fish, worms or crustacea. The albatross and the majority of' petrels utilised cuttlefish of various species, and the remainder fed on crustaceans. Some penguins fed on fish and others on crustaceans such, as kril (whale food). Other birds captured insects or organisms living between tide marks, while some w T ere scavengers apd others were fish eaters. Amongst the external parasites obtained were species of marine leeches and parasitic crustacea from fish; and mallophaga (or feather lice), and ticks from birds. Many internal parasites | were taken and included' tapeworms, I chiefly from seals, albatrosses and I petrels; flukeworms from fish; and j various round-worms from seals, birds jand fish.