Fish Population Studies

Generally, we hear such questions as "what is the magnitude of our oil sardine or mackerel resources?" "Can we get more catch from these resources?" It is, therefore, proper that we carefully examine what is meant by a fishery resource e. g., oil sardine or mackerel resource. A fishery resource is just like any other natural resource (e. g., mineral resource, hydro-electric resource etc.) which is exploited by man. But at the same time, it differs considerably to character from other types like mineral resources. The coal resource in a region is limited in magnitude, even though sometimes we do not know the magnitude. From this fixed resource we can exploit at any desired rate. The resource will be completely exhausted after a period of time depending on the rate of exploitation. In this sense a mineral resource can be described as a non-renewable natural resource which is liable to get exhausted after some period of time. It is also a static resource because we always know how much of the resource remains, once we know how much has been removed. A fishery resource is very much different in character. It is a self-regulating renewable natural resource. Consider a fish population occupying a certain area of the sea. Now when a certain portion of the population is removed, the remaining portion in the habitat gets better food, more area to move about, and this results in faster growth rate, lesser mortality rates and also the spawns get better chance of survival- The result is that the resource resuscitates itself quickly. Apart from fishing, the population is also affected by many other fishery-independent environmental factors such as available food supply, change in salinity, temperature of the water, change in ocean-currents etc. Thus the fishery resource is a dynamic resource, ever changing due to impact of fishing and other fishery-independent factors

A note on the production trend of marine shrimps in India

The paper reviews the production statistics of marine shrimps in the different maritime states of India from 1950 to 1962. It is pointed out that for a correct appraisal of the status of any fishery, it is necessary to have data on effort E and catch per unit effort in addition to the conventional data on catch C. A relationship between U and E has been developed and the status of the fishery of Metapenaeus dobsoni has been discussed in this connection with reference to the data on catch and effort obtained from trawler operations off Cochin

The Indian mackerel; V Population

Pradhan (1956) examining the mackerel landings at Karwar from 1948-49 to 1952-53 concluded that the sex composition of the commercial catches during the fishing season was roughly as 45% male and 55% female. Similar qualitative statements regarding sex distribution of commercial landings at various specific centres are available in the annual reports of the Central Marine Fisheries Research Institute. In 1965-66, the sex ratio studies at Cannanore indicated that the proportion of males was slightly higher than females (53.18:46.32) in the adult population. The predominance of males was also seen in Juveniles (modal size 135 mm). In the medium sized fish (modal size 205 mm) which contributed to the bulk of the catch, the sex-ratio was in the reverse order (40.7M;59.3F). In the same year, at Cochin females dominated the catches except for April and September (Central Marine Fisheries Research Institute Annual Report 1966). In 1966-67 season, the sex ratio during the fishing season was found to vary though in some centres was almost equal (Cenrtal Marine Fisheries Research Institute Annual Report 1967). In the first half of 1967-68 season, the sex-ratio of a sample analysed at Karwar showed that females were more numerous. At Mangalore, males were more numerous in the aggregate. Sexes were almost equally represented at Cochin and Cannanore. At Vizhinjam males were predominant in March. In the second half of the year, at Cannanore the females increased to more than twice that of males (Central Marine Fisheries Research Institute, Annual Report 1968). The above excerpts will show that there is no uniformity in the sex distribution in the commercial catches either among various centres or between various fishing seasons. In the absence of

On the relative fishing power of trawlers operated off Cochin

All vessels do not have same fishing power. The absolute fishing power of a vessel is measured in terms of the fishing mortality generated by it. But since the latter cannot be measured directly, a relative fishing power of a vessel has been defined as the ratio of the catch per unit fishing time of the vessel to that of another fishing vessel taken as standard when both are fishing on the same ground and the same density of fish. In this way, a fishing power can be allotted to each vessel. Once the relative fishing power of different vessels are known, it will be easy to Compute the total intensity of fishing effort, an accurate estimate of which is so essential in the study of stock assessments of fisheries

Survey of the sea fisheries of India

A preliminary account is given of the design and technique of the sampling method employed for estimating the landings of sea fish at some selected centres along the East and West coasts of India. Statistics of marine fishing villages, fishing populations, boats and nets are presented along with app roximate percentages of the occurrence of important fishes and also the estimated monthly landings of fish during 1949 at some representauve places