The evaluation and management of fisheries resources requires knowledge of spatial and temporal changes in the habitat-associations of fishes as well as studying the biology and dynamics of commercial fishes of that fishery. The thin lip mullet, L. ramada is one of the most important and high valued species in Bardawil lagoon, Egypt. Long term commercial catch statistics show a significant decrease in the commercial landings of grey mullet in Bardawil lagoon since 1995. By learning more about this species and protecting the habitat upon which it depends, we can ensure that this important valuable fish remains abundant. Age was determined based on scale's readings of fish collected in May 2017 to December 2017 and in May 2018 to October 2018. Growth parameters, mortality rates, exploitation level as well as the critical lengths and ages were estimated. Based on yield per recruit analysis, the mullet fishery in Bardawil lagoon was found to be heavily exploited. The study suggested some applicable reference points for sustaining and optimizing the thin lip grey mullet yield in Bardawil lagoon.
The lakes’ fisheries play an important role in the Egyptian economy. Egyptian lakes face many challenges such as over-fishing, illegal and destructive fishing methods, human activities and pollution which affected the fish production from it. The lakes’ contribution to the Egyptian fish production decreased from about 50% in 80’s to the only 10% during 2017. Lake Nasser, as one of the largest artificial lakes in the world, plays a significant role in Egyptian fisheries. Its mean annual fish production is about 28,000 ton, this constituted 18% of the total fish harvested from Egyptian lakes. The catch and effort data over 15 years were collected from the lake and analyzed to assess its status and to summerize the main problems facing its development and management. Maximum Sustainable Yield of Nasser lake with special reference to the Nile tilapia, the main species in the lake, is estimated based on catch and effort data from 2003 to 2017. The computer software packages of ASPIC had been used. The surplus production model of Schaefer was applied in this study. The obtained results proved the over exploitation situation for the lake fishery and to achieve the sustainability many applicable measures are recommended.
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Keywords:Lethrinus lentjan Age Growth mortality rate Red Sea Egypt Age, growth and mortality are very important parameters for rational exploitation and management of the fish population. Age, growth, mortality and exploitation rates were studied to assess the current status of the redspot emperor Lethrinus lentjan stock in the Egyptian sector of Red Sea. The study was based on a total of 943 specimens that collected during 2014 and 2015 with total length range of 11.5 to 50.7 cm. Results showed that, the maximum life span of L. lentjan in the Egyptian Red Sea was 6 years and age group one is the most frequent one forming up to 54% of the total catch. L. lentjan attains its highest growth in length at the end of the first year of life (24.45 cm) after which the annual increment in length decreases gradually with the further increase in age. The b-value of length-weight relationship was estimated at 3.03 indicating a tendency towards isometric growth. The composite coefficient "k c " and the relative condition factor "K n " were fluctuated according to different fish length groups and months. The length at first capture was L c = 20.11 cm with corresponding age T c = 0.58 year. The total mortality of L. lentjan (Z= 1.52/yr), natural mortality (M = 0.35/yr) and fishing mortality (F = 1.17/yr) were lead to an exploitation ratio of E = 0.77. The high values of both F and E are reflecting the high level of exploitation of this species in the Egyptian Red Sea waters.
Clariid catfishes are of great economic importance as protein food in adequate prices. For several years, species of the genus Clarias (Scopoli, 1777) have been used in local fish culture, where they proved to be a fast growing protein source. Age, growth, mortality and relative yield per recruit of Clarias gariepinus in Lake Manzalah, Egypt, were investigated. The maximum life span based on otoliths' readings was 8 years, while the von Bertalanffy growth parameters were L∞= 86.88cm, K= 0.31/year and t 0 =-0.39 year. The mean annual instantaneous total, natural and fishing mortality coefficients were 0.98, 0.37 and 0.61/year, respectively. Accordingly, the exploitation ratio was 0.62, which was higher than the optimum one. Relative yield per recruit analysis revealed that C. gariepinus is over exploited in Lake Manzalah where the E 0.5 was lower than the current one (E 0.5 = 0.35). Some recommended management actions should be applied to strengthen the ban of fishing in the spawning season or in the nursery ground and to adopt a legal minimum size to protect the young and small-sized fish. In addition, to make any regulation more effective, all stakeholders (fishermen, scientists, non-governmental organizations and policy makers) should work together to establish a comanagement plan to conserve this valuable stock.
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