128 resultados para biologia pesqueira


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The present study deals with the performance of shrimp in shallow waters in Sofala Bank presents both seasonal fluctuations as well as fluctuations year to year. These variations may be due to several reasons: abundance of shrimp, fishing effort, fishing techniques and environmental conditions such as the turbidity of the water, tides, temperature and salinity.

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The paper presents the results of a survey carried out in the water of Angoche, Quelimane and Beira referring to the fishing methods used to catch shrimp in the Sofala Bank.

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The shallow-water shrimps represent the most economical resource in Mozambique. Therefore, annual surveys have been carried out to investigate the state of the stock, the fishing methods for a better analyses catch/effort statistics. Resource assessment was conducted on principal species - Metapenaeus monoceros and Penaeus indicus - to estimate levels of abundance and distribution in the Sofala Bank.

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The paper deals with the proper management of fishing resources of shrimps in shallow waters, those currently constitute the main source of foreign currency trade of the country. The analysis of the level of the productive sector is presented by the local Institute of Fisheries Research.

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Although it is known enough of the biology of shallow+ waters shrimps, knowledge of the deep-waters shrimp is still limited. This is due to the fact that: these resources are relatively new and the study of deep waters species is more difficult and expensive. Some biological informations on the main species of shrimp in depth of Mozambique have been collected during investigation cruises (Sports et al., Pacule, 1987) and through sampling carried out on board commercial vessels (DDR fleet) between 1983 and 1986.

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The species Palinurus delagoae is distributed at 17 °00' S of latitude, at a depth greater than 200 meters. However the main area with a fishing intensity station is located at 22°00'S of latitude from 200 and 400 meters. The fishing of these resources is made with cages and trawling nets.

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In volume 60 of the FAO Statistical Yearbook of Fisheries, we can see that the world shrimp catch in 1985 was 1.9 million tons. This represents an increase, since 1980, of 250 tons (15%). Catches of shrimp is about 2.5% of global marine fishery products. But as we know, its economic value in the global market is much higher, reaching a value of 30%.

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The total abundance of small pelagic species in Mozambican waters was estimated to be 100 (plus or minus 45) thousand tonnes of which scad and mackerel constituted 57 (plus or minus 39) thousand tonnes. These abundance estimates must be considered as minimum estimates of biomass as the efficiency of the trawl was assumed to be equal to 1.0.

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The results obtained during the third phase of Nauka are reported concerning the standing stock estimates, population length structure and gonad development of scad and mackerel stocks and the catch composition in Mozambican waters.

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The fishery for scad and mackerel along the coast of Mozambique began as a licensed fishery in 1977. In 1980, Mosopesca, a joint venture between Mozambique and the Soviet Union was formed and the licensed fishery ceased. Mosopesca started fishing with four vessels, but since 1984 the number of vessels has gradually been increased and at the end of 1985 a total of seven vessels was in operation. This report contains an updated assessment based mainly on information collected from July 1984 to May 1986.

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The worldwide shrimp landings in 1988 were reported to be 2.484.000 tons an increase of about 460.000 tons compared with 1985. The majority of shrimp fishing areas located in the tropical and sub-tropical regions with a contribution of more than 2 million tone. The most important species are the shallow water Penaeid shrimps. This quantity of about 2.5 million tons represents approximately 3% of the world marine catch. In terms of value, it represents almost 30% of the world trade in fish products. Main management objectives include: long term resources conservation; to maximize physical catches; to maximize the total income from catches or foreign exchange; to maximize economic profits; to reduce the shrimp by catch or improve its utilization; other social and economic interests. These objectives are in part interconnected and some are in conflict. Resource conservation is a basic condition for all other management objectives. Management policy definition should be in accordance with national goals and based on available scientific knowledge of the resources and of the fishing industry. The definition and selection of management objectives is an important process, to which the scientists must contribute the best way they can, mainly in providing the necessary information and options for management.

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A summary of the shrimp fishery history as well as the most important recommendations for the period 1977-1990 is presented. During the last years the catch rates have decreased. Although many possible causes can be appointed, such as, weather conditions and increase of effort, there is no clear explanation for it. A relationship between catch rates in the main period of recruitment (January to March) and the level of recruitment of the same year was established. Based on this relationship, the total annual catch is predicted for the level of fishing mortality chosen. Fishing mortality is estimated as 2.28 yearˉ¹ and a gradual reduction of fishing effort is recommended until 2.17 yearˉ¹ calculated as F(sub)0.1.

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Biological effects of management measures introduced in the shrimp fishery from 1985 to 1990 are analysed as well as the results from simulation of different closed seasons. Observed changes in recruitment, total catch, biomass and average individual weight during 1985 to 1990 for Penaeus indicus and Hetapenaeus Monoceros are also analysed. Further studies on a stock-recruitment relationship are important due to decline of recruitment levels in this period. A three-month closed season starting in January is recommended, without increases in the monthly fishing effort. The TAC shall be fixed according to the recruitment level each year.

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The objective of this study is to recommend management measures for the industrial shallow-water shrimp fishery in Sofala Bank after estimating the economic affects considering different alternatives and assessing the level of exploitation of this fishery. The short-term economic analysis was based on the results of the total catch and average weight of the shrimp caught obtained by a simulation model in which different combinations of exploitation patterns and levels of fishing intensity were tasted. The variable parameters used were the mash size and the duration and period of the closed season, and all the remaining parameters were fixed. Economic and production data of the main industrial shrimp fishing companies for the period 1987-90 were also used.

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An estimation of the total industrial catch of the shallow water shrimp by-catch for the period 1986-1990 is presented. By-catch species compositions based on landings and onboard samples at ex-Emopesca/Beira (Marbeira) and Pescamar are also presented. The by-catch is essentially composed by 2nd and 3rd commercial fish categories, other crustaceans and cephalopods appearing in varying proportions in the catch. The total catch of shrimp by-catch estimated for the period is approximately 17 to 25 thousand tons per year.