A SURVEY OP ?'HE PELAGIC FISHERIES OF THE WORLD Part I: GENERAL CONSIDERATIONS BY H. Srinivasa Rao INTRODUCTION the Gulf of Mexico and the Carribbean Sea, and (2) the Pacific and Indian Oceans with their con- It has been a great privilege to be asked to open nections in the South with the Antarctic, and with the discussion on the World Pelagic Fisheries in the a northern connection for the former Ocean with symposium arranged by Dr. G. L. Kesteven as part the Arctic by the Behring Sea. The Red Sea, the of the proceedings of the Singapore Inaugural Meet- Arabian Sea, the Bay of Bengal and the Andaman ing of the Indo-Pacifi~Fisheries Council. The litera- Sea, the China Sea, the Sulu Sea, and the Java, Sunda, ture on the subject is very extensive, and scattered Arafura, Banda and Celebes Seas of the East Indies in many books, journals and periodicals published in and the Japan and Yellow Seas are more or less the five continents. Owing to the shortness of land-bounded. notice for the preparation of the paper, it has not been possible to review any but a fraction of the Oceans of the The oceanic mass of water literature on the subject, and no one is more con- world as a thus constitutes for marine organ- scious than myself of the incompleteness and inade- corr tinuous isms a sinrrle continuous domain L. quacy of the paper presented. I hope, however, that domain for whose populations are, as a rule, ef the more salient features of the subjecx: have been marine organ- greater density in the upper strata touched upon in this brief review, and that these isms. of water than the lower, and exhi- will lead to a fruitful discussion. I should like to bit in the former a greater diver- take this opportunity to offer my sincerest thanks to sity of form and organisation. With the exception Dr. G. L. Kesteven, F.A.O. Regional Representative of a few of the higher forms of life such as the seals, (Fisheries) for every encouragement and for readily whales, dolphins, turtles, snakes, which have second- placing at my disposal a list of bibliography on the ariIy adapted themselves to life in the sea, the subject which lie had prepared, and to my colleague, majority of sea organisms have the ocean as their Dr. N. K. Panikkar who, at very short notice, was original home. This marine domain or bio-cycle has able to get together a considerable part of the locally been estimated to have about 300 times the habitable available literature at Madras and to prepare a .general space provided by the terrestrial and fresh water bio- connected account of the biology of pelagic fishes cycles together. It may be broadly divided into the from his own and my notes on the subject. primary and secondary biotic divisi0.n~ based upon the physical nature of the sea or upon the nature of The paper is presented in two parts: (1) the biota. - General considerations of the pelagic environment as influenced by latitude, climate, currents, tides, and Physical and The two primary divisions of the biological and physico-chemical contents of the biological the oceans are (I) the benthic in- sea and their influence on fish and fisheries; (2) Bio- divisions of cluding all the ocean floor and (2) logy of pelagic fishes, chiefly of the shoaling forms the oceans. the pelagic including the whole such as herring, mackerel, horse-mackexel, flying fish, mass of water. Although this so far as is known and has been possible to gather article deals specifically with the latter division, the in the short time at our disposal. physical and biological continuity of the marine domain or bio-cycle makes it necessary that the Geograjhical . The pelagic region of the characteristic features of both the divisions be taken divisions of oceans is a part of the marine bio- into account if the significance of factors affecting the oceans. cycle of the world which may be pelagic fisheries is to be fuily understood. The pela- divided geographically into two gic division is further sub-divided into the hTeritic main divisions, viz (1) the Atlantic with and the Oceanic regions corresponding to the lit- its connections in the North and the South toral and the abyssal sub-divisions of the benthic, with the Arctic and Antarctic waters res- in reference to the depths to which light penetrates pectively, and the associated partially land-girt seas- the neritic and oceanic regions and to the extent and the North Sea, the Baltic Sea, the Mediterranean Sea, depth of the continental shelf. These are not, how- ever, absolute divisions as depth of penetration of the sea. It has been shown that the ~eri~h~ticbac- light in the neritic region may be affected by the terial population of pelagic waters has a tendency to turbidity conditions of the sea and the extent of follow closely the distribution of plankton ensuring the continental shelf may be correlated with the thereby the thorough decomposition of dead plank- geological formation of land masses and the extent tonic organisms even before they have had time to of terrigenous deposits brought in by rivers. sink to great depths and the regeneration of miner- alized plant nutrients in the upper layers of water Physical and Fishes of both the benthic and both in and below the eu~hoticzone. The upper biological the pelagic divisions of the ocean layers of water have however a relatively poor con- characteris- have to depend for .their sustenance centration of nutrients as compared to the bottom tics of the on the organisms and organic sub- layers, more particularly in the interface between benthic div- stances produced in it either in the mud and water, unless augmented with nutrients isions of the form of plants or animals or in from the bottom by processes of vertical diffusion, sea. the form of organic detritus. The convection overturn and upwelling. benthic division from the shore to the abyss is usually covered by Biological The oceanic pelagic life is sedimentary terrigenous deposits, organic or pelagic characteris- made up of animals independent oozes, and red clay. Except for the fact that the tics of the of the bottom throughout their deep sea deposits, consisting of nutrient organic and oceanic regions development (Radiolarians, Fora- inorganic matter, may be brought within the range of the pelagic minifera, Hydromedusae, Siphono- of the neritic region by upwelling and currents in division. phores, Ctenophores, Chaetognaths, the ocean, the terrigenous deposits restricted to the . copepods and hyperines among configuration of the continental shelf seem to influ- crustacea, heteropods, pteropods, appendicularians, ence the greater productive capacity of the coastal salps, pyrosomas, some sharks; a great number of bony region in reference to fisheries. Plants are the real fishes with air-bladder and some without, and the sustainers of animal life in the sea in general, and whales). The neritic pelagic includes, in addition the production and distribution of plants in the sea to the above, animals which are dependent on the depend upon a great variety of factors chief among bottom during part of their existence (medusae with which are light and available nutriment in the biotic alternating generations, Iarvae of benthic animals, division in which they occur. The eulittoral zone floating eggs of many fishes, water fleas, Podon & of the benthic division which can support large Evadne whose eggs sink to the bottom, and the ostra- attached plants constitutes only about two per cent cod Philomedes and numerous other free-living crus- of the sea floor, and even here unfavourable sub- tacea). Many cephalopods, most sharks and rays, stratal conditions restrict the production of such many bony fishes of the neritic pelagic are included plants, which rest at the bottom at night. The sea turtles, seals and walruses which belong to the pelagic region The function of primary food production in the feed on benthic forms. The time and season of sea therefore devolves on the unattached floating dependence on the bottom vary with different ani- plants, e.g. phyto-plankton-such as, algae, diatoms, mals so that periodic changes in the composition of aagellates, coccolithophores, etc. which occur in the neritic pelagic are much more pronounced than enormous numbers. The phytoplankton may be the.oceanic. The outer seaward boundary of the divided broadly into neritic and oceanic populations. neritic pelagic, is generally the 200 metre contour As the conditions of salinity, temperature, turbidity of the benthic region, and includes the banks as and other environmental factors vary considerably in well as coastal waters. This boundary is the obvious the neritic region as contrasted with the more stable result of dependence on.the bottom. Inhabitants of conditions in the oceanic region, it may be supposed the neritic and oceanic pelagic are usually mixed at that phytoplankton production in the coastal belt the boundary, and currents carry nexitic forms out may be adversely affected, but in actual fact the and oceanic ones in, generally to their destruction, waters of the neritic region are believed to be fifty although the eels are a notable exception. times more productive than the open oceanic waters (Lohmann, 1908) as substantiated by the abundant As the Maximum production of phytoplankton benthic and pelagic fauna in the former. The pro- is restricted to the lighted zone, animals of the pela- duction of phyto-plankton is in general conditioned gic region, whether aduit or lgvae, which perma- by light and latitude, and by available nutrients in nently or temporarily live in it to feed on phyto- solution.