Potential Catch Research Articles

The living pelagic resources of the Americas

Abstract Annual catches of pelagic organisms, excluding marine mammals, from the Atlantic and Pacific waters surrounding the Americas for the period 1969–1971 averaged 17, 000, 000 metric tons. Catches of the pelagic organisms from the Pacific alone were nearly 14, 000, 000 tons. However, considering the recent drop in the catches of the Peruvian anchovy, the data for 1972 and 1973 when compiled, will show a drastic decline in the catches of pelagic species. Catches from American waters are compared with those from other waters and their relationship to the area and population of the Americas is examined. The potential maximum catch of pelagic organisms currently utilized is projected to 26, 000, 000 tons, whereas if the markets and fishing technology could be developed for non‐conventional species, then it is estimated that the catch could be increased to 42, 000, 000 tons. Rational utilization of the pelagic resources of the Americas necessitates conservational and managerial measures. This in turn call...

Development of Fisheries for Traditionally Exploited Species

Present catches of traditional marine resources are characterized by a great predominance of pelagic species, especially among the fishes. Since World War II the catch of pelagic fishes has increased by 27.5 million metric tons (mmt) and now constitutes about 70% of the total; production of demersal species has increased by 10.5 mmt. Over 60% of the catch is of plankton-feeding organisms, a little over 25% is predacious fishes, and only 4% bottom feeders.Of the world catch of aquatic organisms in 1970, 63.4 mmt (90%) was fish, 5.2 mmt invertebrates, about 1 mmt whales, and 0.7 mmt seaweeds. About 90% of this catch was from the ocean. From 1950 to 1970 marine catches rose from 16.1 to 55.8 mmt, while those from fresh waters increased from 2.4 to 7.6 mmt.About 70% of marine catches are made up of seven families of fishes, with the Engraulidae having by far the leading role — about 24%. Next in order come Clupeidae and Gadidae. Pleuronectidae, Scorpaenidae, Sparidae, etc. are less important. Only 5.06 million tons (8%) of the catch is of invertebrates. Of these 65–70% are molluscs (mostly squids), 30% crustaceans, and 1% echinoderms.Species such as cod, redfish, rockfish, flounders and clupeids in most areas of the northern hemisphere have reached or almost reached their limit. The greatest increase in demersal catches can be expected from the Falkland–Patagonia area, where landings of hake, poutassou, grenadier, and some other species could reach 3 million tons, and in New Zealand and Australian waters the take may rise to 4 or 5 mmt. Pelagic fishes may eventually yield catches of the order of 17–20 mmt, including sardines, anchovies, mackerels, carangids, sauries, smaller tunas, myctophids, and squids. In all, a future catch of 52 mmt of pelagic species and 30 mmt of demersal species may be possible.In addition, perhaps 1 mmt can be expected from fishing in depths of 800–1200 m for macrurids, rockfsishes, halibuts, etc. The yield of demersal invertebrates may reach 2.2 mmt, anything more would require extensive aquaculture.A total potential catch of 90 mmt of familiar species is estimated — not including krill, other zooplankton, or seaweed. This figure implies adequate and effective conservation regulations, without which catches can be expected to decline rather than increase.

Maximum Sustained Yields from Fluctuating Environments and Mixed Stocks

Using numerical models, effects of environmental variability upon yield were tested for six single-age fish stocks characterized by different kinds and degrees of density-dependent reproduction potential. The two levels of variability examined had extremes of yield standing in the ratios 7:1 and 18:1, respectively. Close regulation of fishing to the optimum percentage for each year's stock improves the long-term average catch taken, the improvement being the greater, the more variable the environment. With the higher level of variability, improvement in average catch among five of the stocks ranged from 26% to 79% increase. However this increase in mean catch is achieved at the expense of increased variability in catch from year to year—in fact, for some kinds of stocks there must be complete cessation of fishing in some years in order to get the long-term maximum. The yield of stocks, in which reproduction per spawner declines at low levels of abundance, is particularly improved by a close adaptation of fishing effort to the supply of fish available.When two or more populations of a species, characterized by different reproduction potentials, are fished in common, total potential catch is less than when each can be fished separately at its optimum level. If a common fishery cannot be avoided, the achievement of maximum average yield may find one of two originally-equal stocks as abundant or even more abundant than before the fishery began, while the other may persist only at a low level or even be exterminated completely.