Penaeus indicus H. Milne Edwards, 1837: resumo das conclusões dos cruzeiros de pesca exploratória entre 1979 e 1983 no banco de Sofala em Moçambique

From 1979 to 1983, several surveys were carried out with research and fishing vessels at Sofala Bank in Mozambique. Their main objective was the assessment of shallow water prawn stocks, as this resource is of great economic importance for the country. A summary of the conclusions of these surveys regarding the species Penaeus indicus is presented. During the rainy season the species occurs closer to the shore than during the dry season. Estimates of biomass are very variable. The spawning peak seems to occur at the beginning of the rainy season (September-October). The spawning areas are located very close to the shore in the northern part of Sofala Bank and South of 17 degree 10'S in the 15-25 m depth interval.

Penaeus indicus H. Milne Edwards, 1837: a summary of the conclusions from the fishing exploratory surveys between 1979 and 1837 at Sofala Bank, Mozambique

From 1979 to 1983, several surveys were carried out with research and fishing vessels at Sofala Bank in Mozambique. Their main objective was the assessment of shallow water prawn stocks, as this resource is of great economic importance for the country. A summary of the conclusions of these surveys regarding the species Penaeus indicus is presented. During the rainy season the species occurs closer to the shore than during the dry season. Estimates of biomass are very variable. The spawning peak seems to occur at the beginning of the rainy season (September-October). The spawning areas are located very close to the shore in the northern part of Sofala Bank and South of 17 degree 10'S in the 15-25 m depth interval.

Yield isopleths of Tilapia esculenta Graham 1928 in Lake Victoria and Tilapia nilotica (Linnaeus) 1757 in Lake Albert

The yield equation given by BEVERTON and HOLT (1957) has several parameters which are difficult to estimate for tropical freshwater fish species. Nevertheless, some simplifying assumptions can be made and the most relevant parameters used to enable the construction of yield isopleths. Tilapia esculenfa has the following parameters: maximum length (L ∞=33.8 c.m. growth rate (K) = 0.32, natural mortality rate (M)=0.17 and the length at maturity (1 m)=22 cm. The optimum yield is obtained by catching the fish at a length of first capture of 26 em and a fishing mortality rate of 0.5. Tilapia nilotica with L ∞=49 cm, 1 m=36 cm, K=0.50 and M= 0.30 gives optimum yield when caught at a length of first capture of 35-36 cm with a fishing mortality rate of 0.5-0.6. The stuned Tilapia nilotica of Lake Albert has L ∞=17 cm, K=2.77,1 m=12 cm and M=3.37. With such a very high natural mortality, maximum yields would be obtained hy using a length of first capture less than 9 cm and a fishing mortality rate exceeding 1.8.

On the ecology and explorations of the fisheries of an East African rift valley lake, Part 1: On the bionomics and population structure of Tilapia nilotica Linnaeus 1757 in Lake Baringo, Kenya

An ecological survey of the fisheries of Lake Baringo, Kenya was carried out between August, 1972 and August, 1973. The bionomics and population structure of T. nilotica is described. Sampling was done with multifilament gillnets of graded mesh sizes from 51 mm to 178 mm in approximately 12.5 mm increments. The Lake was divided into three sampling and ecologically different zones - the south, central and north zones. The size range of T. nilotica of both sexes caught was between 5 and 27 cm (mode 16 cm) with a mean length of 16.07 cm. For all the collections, males dominated (55.3%) and a higher proportion of males were caught in January, August and November. The smallest mature male and female was 9 and 10 cm respectively. Males grow faster and mature at larger sizes than females. 50% of all males and females mature at 17.4 and 16:4 cm respectively. The periods of intense spawning were between August and October and January to April. The Tilapia were feeding best in central and north zones and the feeding intensity was reduced in January. Two endoparasites Contracaecum sp. and Clinostomum sp. were isolated from the Tilapia. The "condition" of the fish was better in the north than in the other two zones.