INTERPRETATION OF FISH SHOAL INDICATIONS IN THE ARABIAN SEA V. A. Puthran & V. Narayana Pillai Central institute of Fisheries Operatives, Cachill. Jntroduction Some knowledge regardir.g the pre­ sence of similar fishable concentrations Availability of resources is perhaps of fish and other marine life is of great one of the most il1)p~rt2nt factors which importance to the technical ski:] working determines the success of any industry. on board fishing vess" ls. Their technical In the case of the fishing industry, at the knowledoe in fishing could be put to basic production level. the availability use more-eifectively ..,>,hen posit ive indi­ of fishable concentrations of fishes and cations with regard to the avaiiability of other mHine life is the decisive factor shoals are known to them. The correct which c~ntrols the economy of the whole and quick interpretation of these indi­ system. Even when well e quipped cations would Dlace them in a better vessel, fishing gear an d trained person­ position from where they can use their nelare available, the success of the indu­ judgment towards achieving great stry is dependent on the availability of success in this endeavour. fishable concentrations of commercially important marine life at the appropriate In India, only very little werk seems time. By the word' fishable concentra­ to have been done along these lines tions', the implication is availability of especially to arrive at a positive corre­ sizeable quantities of fishes which could lation between certain natural indica­ be definitely caught using a particular tions and presence of fishable concent­ type of craft and gear in a particular rations of comITl "rciallv important area at a particular time. Naturally, with marine life, especially the shoaling the availability of fishable concentrations fisbes. The work done by Ba lan (1 961 ) of comnercially important marine life, is worth mentioning in th is context the chances of getting a good ca tch are where the autho r has ma de certain always high. He nce it assumes great observations on the shoalir:g behaviour significance at the basic productio n of the oil sardine of! Calicut along the level of the industry, Kerala coast. June, 1974 9 Fish shoals " be two types viz, those which are visi­ ble and those which are not visible, Fish shoals are naturally accumulated The visibility is u sually governed by group of fishes which under nor mal con­ factors such as amount of Ii ght and ditions show a tendency to remain to­ transp arency of the water column and gether. The c ommercial feasibility of above all the depth at which the shoal operating certain specific types of nets moves. Based on their habits, shoaling (Purse seines, Cast net, Ring nets , Ram­ fishes give diffe rent types of indica- pani nets, Patta bala, Mar i bala, Colli tions suggesting their presence ip a 1 vala etc.) is dependent on the availabi­ particular area/depth of the sea. The Iityof fishable concentrations of com­ c orrect interpretation of these indica­ mercially important shoaling fishes. The tions is of great importance as otherwise necessary knowledge regarding the there is every possibility of losing the behaviour of similar shoaling fishes will chances of a good catch, by employing enable us to use the specific type of a particular type of fishing method. fishi ng g9ar m~re effectively, thereby increasing the catches. Absence of such Indications and Interpretations knowledge can result in wastage of valuable time, labour and above all (A) Movement in the surJace waters: m oney. The behaviour of a fish shoal When the shoal moves up in the surface is cer tainly decided by the variations waters small sized r ipples are c reated observed in the various environmental depe nding upon the size of individual factors both mete orological and hydro­ fishes. It is presumed that the d istance graphic, such as dire ction and force of between two successive wave s is more wind, amount of cloudiness, phase of or less equal to d ouble the thickness of the moon and tide, temperature, sali­ individual fishes. They can be spotted nity, dissolved oxygen conte nt. currents, from a distance of 7 to 8 km, a nd are pre sence of organic and inorganic p ar­ usually dark in colour. Fishes which ticles and their intensity and the like. are found in similar shoals are mostly Eventhough, in general, fishes are cat fishes, sciaenids, seerlish, anchovies known to swim against the prevailing barracuda, carangids, macker e l, sar­ curre nts during day time, at night many d ines. gray mullets, etc. of them are found to drift along with the current, sometimes evidently in the (B) Taking water through the mouth midst of food items on which they feed. while moving: During winter when sea water temperature shows a sudden fall, Fish shoals common around Indian certain fishes move towards the sea .ur­ waters could be broadly d ivided into face and while moving they keep their two major groups, viz .. m ouths open half above the water sur­ I) Surface shoals face. Cat fishes, sciaenids , Otolithus sp., 2) Submerged shoals. gray mullets, carangids e tc. belong to this category and can be easily spotted. In the case of the first cate gory, the shoal itself or rather individual fishes (C) Showing the dorsal fin above the (of sufficiently large size) would be water level while moving: This is a typical visible from the d eck of a fishing ve ssel. characteristic of Cat lishes and caran­ Among the second category there c an g ids. 10 &aJood Ezport Journal (D) Flying movemenls above Ihe waler thereby splashing the water surface . If level: Certain fishes when they get the movement is s low, the water move­ frightened or when chase d by other ment caus ed by this splashing wil l r e ­ fishes exhibit flying movements above semble the moveme nt caused by rainfall the water surface, covering distances of at the sea surface. Similar indications 20 to 30 m. at a time. The typical exam­ are characteristic of shoals of anchovies, ples are the flying fish (E xocoetus sp.) carangids, and Ambassis sp. (near fr e sh and fishes like Hemiramphus sp. etc. water outle ts into the sea) (E) Keeping Ihe gills open while moving: (I) Individual fi,ltes CUlling Ihe water While moving in a shoal, fishes like surface and moving back: Sometimes from mackerel and sardines are known to a moving shoal a few of the fishes move keep their gills wide open and move up and cut the water surface by their sideways. t,il and move down to join the shoal. If the sheal is m wing nearer to the sea (P) Splashing nlO vem' nls : According surface, the shoal would b e visible. to the law of nature, bigger carnivorous Fishes like Tuna, seer fish , leather skins fishes feed on smaller fishes. These and carangids give similar indications. carnivorous fishes usually take advant­ age of fish shoals. When the shoal is (J) Shoals which release a thin film of suddenly attacked the smaller fishes oily secretion: O ily secretions are chao show a t9nj9noy to mJ'/e faster to racteristic of waters where shoals of cat escape the predators and while doing fish, sharks rays (espe cially Ae lobates so cause a certain amount of splashing sp.), mackerel, sardine and caran g ids ~ of water at the sea surface. Eg. sar­ are common . Ce rtain varieties also g ive dines, m,ckerel, silver bellies, prawns a peculiar sme ll. One canno t a lways etc. The common predators encount­ expect [he shoal directly underneath ered are Sharks, seer, fish dolphins, these oily patches as these patches are saw fish, leather skins etc. found to move along with the prevailing wind and water currents. (G) Jumping movements: Some fishes are in the habit of jumping above the (K ) Changes observed in the colour of water line, at certain intervals. Some­ surface and bOllom walers : Generally, tim"!s it so happens. that they push the fishes which exhibit coloured indica­ anterior part of their bodies up and tions do not make other visible signs. before the tail portion leaves the water The dorsal surface of a·large number of surface, the head once again plunges fishes in a shoal when seen from the back into the water. Sometimes similar surface reveals specific color Blions movements are repeated .t longer inter­ depending upon the species . In the vals of 5 to 6 minutes. Cat fishes, sar­ case of fishes like pomfrets w hich exhi­ dines, silver bellies, anchovies etc. be­ bit sidew~s motion, the colou rauc n long to this category. exhibited is that of the lateral side. Bottom fish shoals like those of g olden (H) Individual fishes moving up and anchovy reveal a reddish tinge, proba­ splashing the waler surface and then going bly brought about by a comb inatio n of down: In a fish shoal, sometimes indivi­ the dorsal colouration of some of these dual fishes come up and go down quickly fishes and also the reflected-radiation June. 1974 11 from ths .ea bottom . S'Hface fish shoals, resulting water motion at the in general, are bl.ckish in colour. surface can b e so high th a t it can capsize small boats' which The ab~ve said .feature is noticed in the following · varities of fishes go nesr the shoal. viz. Crescent perches, ~harks, sales, (4) When a sufficiently fast moving prawns, white fish. rays, kilirneen, rib- fish shoal moves at the sea bot- bon fishes, polynemids etc.