The principal aim in marine fisheries

Tesearch is to find ways and means of

obtaining 'maximum sustained yield'

from year to year and to practise conservation

procedures for realizing such

an end. By 'maximum sustained yield'

is meant the maximum quantity of

fish th at can be harvested by man in

a given year, without adversely affecting

the regenerating or repleni shing

potentialities of the stock with reference

to future fisheries

Bensam, P

CMFRI Digital Repository

On Judicious Exploitation of Marine Fishery Resources P. Bensam Reader Centre of Advanced Study in Marine Biology Porto Novo The principal aim in marine fisheries Tesearch is to find ways and means of obtaining 'maximum sustained yield' from year to year and to practise con-servation procedures for realizing such an end. By 'maximum sustained yield' is meant the maximum quantity of fish th at can be harvested by man in a given year, without adversely affect-ing th e regenerating or repleni shing potentialiti es of the stock with reference to future fisheries. In taking the maximum sustained yield from a marine fishery resource, not only the quantity of the yield that is taken into con-sideration but also the income or profit gained out of it. Ma.rine fisheries -resources are common property resources and are open for exploitation by any-body. Therefore, the natural tendency ·of the exploiter is to obtain as much production as possible. But, once the l evel of maximum sustained yield is crossed, the ensuing overfishing operat-ions shall lead to a decline in th e reg eneratin g capacity o f th e resource .and end in its deplet ion. Although th is by itself may not lead to extinct-ion of the species concerned, the quantity of yield might become so low as to make . centinuous exploitation of ·the species unrewarding . lMarch, 1980 A marine fishery resource is a self-regulating, renewable, natural resource' denoted as 'dynamic resource' , as different from non-renewable, static, resources such as minerals , oiL etc_. The latter will have to be exploited carefully and with reserve, whereas the former could be exploited without. reserve upto the level of maximum, sustained yield becaus e if the 'exploit-ation falls short of it, the fishes wouldc die of natural causes and become a waste to the fish ery. Under the pres-ent state of increasing demand for marine fish, it is essential that marine-fi sheries resources are conserved. man-aged and exploited most judiciously. FACTORS INFLUENCING SIZE OF A RESOURCE:-There are four primary factors that influ ence the size of a marine fish ery resource . These are: (i) recruitment of new individuals to the population; (ii) grow th of dillerent year· classes eXisting; (iii) deaths due to naturar causes and (iv) dea ths due to fishi ng. operations . By harvesting the resourc es man directly influences the last factor. In the un-fished state, population, levels are balanced by natural caus es; and, as such when fishing begins: most of the yield is derived from the accumulated population. Alter the iishery has operated for sometime, the lowered natural mortality, accelerated ·growth resulting from availability of more food, more space to move about and lower disease and parasite infest-ations, etc bring the population into a new state of equlibrium. If this equlibrium is so lowered as to result in such a state of not having the requisite capacity or individuals to re-pro<!uce and replace the biomass re-moved. then the population would become adversely affected with reference to subsequent fisheries. Therefore, in ·undertaklng fishing operations caution has to be exercised to leave out atleast that much of the parent stock which would be able to give rise to the .optimum yield. Usually, man has absol-:utely no control over facors like diseases, :parasites, changes in hydrographical 'Conditions, etc. And, the only f actor on which man can have some control over a marine fishery resource is his .-own fi shing activities. Und er such a 'Circumstance, the management and/or 'Conservation procedures which man can ~ndertake, are also l imited. PROCEDURES OF CONSERVATION:-The conservation procedures which man can exercise over a marine fi shery lesource may be considered as below (a) Reduction of fishing mortality: The fact that fishing operations are allecting the size of a marine fish .population can be recogizad when the 1etal yield registers a decline, the catch per unit of effort becomes lower and 1he mean size of the fish caught is 'r(luch smaller than during normal times. 'Under such a condition, the only control that a fishery m',nager can exercise to ;10 protect future fisheries from failures is to reduce fishing effort. . However, in cases where fluctuations in fisheries are caused by fishery - ind'mendent factors, reduction of fishing mortality may not have the desired ellect. (b) Selective mortality: In some fisheries, employing sel-,ective types of gear would result in ' the capture of only larger fish and permit the escape of smaller fish thus affording opportunity for them to grow and replenish the fishable stock. Use· of nets with large-sized meshes, sel-ective types of gear such as gill-nets, drift·nets, etc may be resorted to in· this connection . Or when small·sized fish are also required to be caught. a maximum proportion Or quantity alone' per unit may be permitted to be' captured. (c) Closure of nursery grounds: Usually, fish of small sizes do not t end to shoal with fish of larger sizes. Capture 01 small sized fish or using gears that are likely to destroy young on es such as tra w l nets, are not de .. sirable in such cases. Also, closure of these regions for fishing operations is an effective way of conserving the resources. In the south·east coast of U. S. A., trawling operations of estuaries are prohibited until praw n juveniles reach a specified size. (d) Protection of spawning grou'nds: Protection of spawning grounds is possible only if the spawning grounds are well delineated and defined . As capture of potential spawners would also have the same effect as capturing spawners, spawning grounds may have to be closed for. fishing operations Seafood E.xport Journak much earlier than spawning time. In ·ease of fi she s with demersal eggs, the use of demersal gear like trawls scrapping the substratum will destroy the eggs deposited and hence such gears will have to be prohibited. LAWS AND REGULATIONS: -Laws and regulations e'nacted to con serve marine fish ery resources should be aimed at protecting th e stock as well as at getting maximum sustained y ield. This could be accom-plished by eith er reducing or limiting th e catches and by protecting certain seclions of populations. (a) Reducing or limiting catches: This could be accompli shed by lowering the efficiency of individual fishing units, such as si ze of fishing v essel. size and type of gear, closing areas to c~rtain types of gear, limiti ng the sizes of bags, restrictions on fishing time, etc. Also, the number of fishing units may be restricted by exercising a quota system for catches as well as by limiting the overall total quantity -of fish that could be caught. etc. ·(b) Protecting sections of populations: Protecting sections of populations such as young on es is amply justified by biological evidence s. This is achiev-ed by changing the fishing gear to allow the escape of small sizes, by closing spawning grounds, spawning seasons, nurseries, etc. from fishing ·operations, etc. Protection of specimens based on sex or condition is also resorted to such as the noncapture of Jobsters carrying eggs. February, 1980 LONGEVITY AND CONSERVATION:-Fishes with a long natural life-sparr are ava ilable for capture for a longer period than those with a shorter life-span. Based on this f act. capture of-the specimens could be determined .. In the 'case of long -living and late·· maturing species, survival of sufficient spawning stock is effected by maintain-· ing a moderate fishing pressure. In· the case of the short-living and early-maturing spec ies, fecu ndity is usual!y high and a much less proportion of" the total stock can provide enough spawn , And. in fact , in most of the· short-lived marine fishes, it has nor been possible to demonstrate an absolute correlation between the size of the parental stock and that of the progeny_ As only a small proportion of the· population would be enough to re--plenish the exploitable stock, th e goali of management in short· lived marine fishes is to harvest each annual brood at such a size and fate as to obtain maximum profit. However. even in such. cases, the success of renewal of the exploitable stock differs from year to· yea r, mo stly influeoced by environmen-tal conditions over which man can have· no control. Most of the marine prawns. in India, the oilsardine and mackerel can very well be included in this category. Based on these facts, there-does not appear to be any cause for concern with regard to their exploitat-ion as much as possible. POLLUTION HAZARDS:-By polluting parts of sea wti~ sewage and industrial wastes. man is likely to ,destory fish and shellfish re-sources . As such, efforts will have to· be taken and legislation enacted to-prevent pollution affecting exploitable-stocks as well as critical stages in their \ lifehistory. Similarly marine fish stock will have to be Pfotected from the effects of radioactiv ty and discharges irom nuclear fission power plants. is essential to understand the factors affecting their life history, abundance and availbility. And, with the back-ground of a sound knowlede on the biology of the population, it should be possibie to devise methods, procedures and laws for their rational exploitation and conservation. • It may be seen from the foregoing that for judiciously e<ploiting and managing marine fisheries resources, it 12 KING FROG brand is the hallmarks of best quality Indian frozen FROG LEGS If it is high quality frozen Shrimp and Scampi you are looking for MINIRUBY is the brand PACKERS: RUBY MARINE FOODS PALLURUTHY, COCHIN-682005 (INDIA) Cable: MINI RUBY - Cochin Telephone: Offi. 25047 & 24641 Res. 25027 Seafood Export Journal 

On judicious exploitation of marine fishery resources

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On judicious exploitation of marine fishery resources

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