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Investigations on the reproductive biology of Puntius sarana an indigenous species and Tiiapia remialli (melanopleura) an exotic, in an ancient man-made lake, Parakrama Sarnudra (Sea of Parakrama), in Sri Lanka, carried out from February 1978 to May 1979 are presented. The overall female to male ratio in T. rendalli and P. sarana were 1.1:1.0 and 1.5:1.0, respectively. Considerable deviation from the mean ratio was observed and are attributed to their spawning behaviour and migrations. In the larger size groups in T. rendalti males were dominant while the reverse was observed in P. sarana. Both species were found to breed through out the year, with well defined peaks in the case of P. sarana which were coincidental with the main rainy seasons. Both species are multiple spawners, fecundity ranging from 760 to 6160 in T. rendalli with length and weight varying from 18.8 to 25.8 cm and 126 to 380 g, respectively. In P. sarana. with a length of 23.8–38.0cm and a weight of 180–792 g, fecundity ranged between 16,000 and 290,000. 相似文献
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K. B. Chandrani Pushpalatha Mohottala G. Kularatne Jayantha Chandrasoma Upali S. Amarasinghe 《Fisheries Management and Ecology》2021,28(2):112-125
Culture-based fisheries (CBF) are increasingly accepted as strategies for enhancing inland fisheries, especially in tropical Asia. In Sri Lanka, CBF development in irrigation reservoirs has gained momentum due to concerted efforts of government fisheries authorities for inland fisheries enhancement. In the present study, production trends of five irrigation reservoirs of Sri Lanka before and after the introduction of CBF were investigated and apparently optimal CBF yields were not realised. Hence, the stochastic frontier production function (SFPF) was employed to quantify technical efficiencies (TE) of CBF. For each reservoir, annual averages of input data from 2005 to 2018 (14 years) were used in the TE analysis. Hence, total sample size for estimation of SFPF was 70. Although CBF production gradually increased in all five reservoirs from 2005 to 2018, there were substantial variations of total fish production across the reservoirs. The SFPF indicated that CBF production could be further increased through more efficient management of inputs (i.e. number of fishers, mean number of fishing days per year and stocking density). 相似文献
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Selection of scale for Everglades landscape models 总被引：3，自引：0，他引：3
This article addresses the problem of determining the optimal “Model Grain” or spatial resolution (scale) for landscape modeling
in the Everglades. Selecting an appropriate scale for landscape modeling is a critical task that is necessary before using
spatial data for model development. How the landscape is viewed in a simulation model is dependent on the scale (cell size)
in which it is created. Given that different processes usually have different rates of fluctuations (frequencies), the question
of selection of an appropriate modeling scale is a difficult one and most relevant to developing spatial ecosystem models.
The question of choosing the appropriate scale for modeling is addressed using the landscape indices (e.g., cover fraction, diversity index, fractal dimension, and transition probabilities) recently developed for quantifying overall
characteristics of spatial patterns. A vegetation map of an Everglades impoundment area developed from SPOT satellite data
was used in the analyses. The data from this original 20 × 20 m data set was spatially aggregated to a 40 × 40 m resolution
and incremented by 40 meters on up to 1000 × 1000 m (i.e., 40, 80, 120, 160 … 1000) scale. The primary focus was on the loss of information and the variation of spatial indices as
a function of broadening “Model Grain” or scale.
Cover fraction and diversity indices with broadening scale indicate important features, such as tree islands and brush mixture
communities in the landscape, nearly disappear at or beyond the 700 m scale. The fractal analyses indicate that the area perimeter
relationship changes quite rapidly after about 100 m scale. These results and others reported in the paper should be useful
for setting appropriate objectives and expectations for Everglades landscape models built to varying spatial scales. 相似文献
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In a field study in an upper mountain rain forest in Sri Lanka leaf litter decay rates for nine tree species were measured using the standard litterbag method. The leaf species showed a wide variation in decomposition rates with k values ranging from 0.19 to 9.6 (t0.99 values ranging from 0.5 to 24 years), but it was possible to recognize fast, medium and slow decomposition groups. While there were considerable differences in physical and chemical litter properties these were poor predictors of decomposition rates. There was considerable variation in the N, P and lignin contents of mature green leaves and freshly fallen dead leaves of the different tree species. Percent resorption of N varied from 0 (one species) to 56 and of P from 0 (three species) to 73. There were no consistent patterns of nutrient mobilization and net release of N and P in the five leaf litter species studied. 相似文献
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