Upali Amarasinghe | University of Kelaniya (original) (raw)
Papers by Upali Amarasinghe
Sri Lanka Journal of Aquatic Sciences, 2016
The grey mullets (Family: Mugilidae) have been described as plankton feeders, herbivores, omnivor... more The grey mullets (Family: Mugilidae) have been described as plankton feeders, herbivores, omnivores, slime feeders, foul feeders, bottom feeders, etc. In general, grey mullets are known to be benthic feeders. During a comprehensive trophic ecological study of fish assemblages in brush-parks in the Negombo estuary, Sri Lanka, carried out from 2014 to 2016, a food item that was not found in the aquatic environment, such as zooplankton, phytoplankton, macrophyte or detritus, was observed in the gut contents of mugilids. In this communication, the authors report that the frequency of occurrence of these peculiar items in the gut contents were shedded gill epithelia. Even though shedded gill epithelia were not considered as a food item, they were the most common item in the stomach contents contributing to 49.9% of the mean volume of stomach contents.
Asian Fisheries Science
Growth and mortality were estimated from the length-frequency data of Oreochromis mossambicus fro... more Growth and mortality were estimated from the length-frequency data of Oreochromis mossambicus from the gillnet fishery of Parakrama Samudra, a manmade lake in Sri Lanka, separately for its three basins. The asymptotic length (L_) and the growth constant (K) of 0. mossambicus in the northern basin of the lake (34.9 cm and 0.3, respectively) are appreciably different from those in other two basins (middle basin, L.. = 38.8 cm and K = 0.24; southern basin, L.. = 40.6 cm and K = 0.22). Total mortality rates in the northern, middle and southern basins are 2.22, 1.64 and 1.07, respectively. The spatial differences in growth are suggested to be due to different fishing pressure and environmental conditions. Yield-per-recruit analyses indicate that in the populations with low I.._ and high K, exploitation level should be maintained at a low level. Fish yield could be optimized by increasing the size of first capture and exploitation rate in the populations with high L.. and low K.
Participation of community groups is one of the main requirements for culture-based fisheries (CB... more Participation of community groups is one of the main requirements for culture-based fisheries (CBF) in non-perennial reservoirs of Sri Lanka. Homogeneity of the group characteristics facilitates to arrive at collective decisions. And as such can be considered as positive feature for development of CBF. In this paper an attention made to identify the most important social and economic characteristics affecting the group decisions for development and management of CBF in non-perennial reservoirs of Sri Lanka. Principal component analysis (PCA) revealed that out of 25 measured parameters only 4 namely, the group size of fishers, participation rate in fisheries activities, caste of community and participation rate for regular meetings, were important in determining socioeconomic heterogeneity of the sample. Average income derived from CBF was appreciably high in communities with small group size and high participatory level in-group activities. Contingent evaluation of willingness to pay also demonstrated that the involvement of more people with fishing attitude would be preferred for the successful CBF activities. This analysis indicates that socioeconomic characteristics of rural communities can be meaningfully used for selecting non-perennial reservoirs suitable for development of CBF in Sri Lanka.
Fisheries Research, 2009
The conference 'Fish Stock Assessment Methods for Lakes and Reservoirs: Towards the True Picture ... more The conference 'Fish Stock Assessment Methods for Lakes and Reservoirs: Towards the True Picture of Fish Stock' (FSAMLR) was held in September 2007 in Ceske Budejovice, Czech Republic. A total of 110 participants from 34 countries attended the meeting and 93 lectures were presented. Great advances were reported in fish surveys using hydroacoustics and multimesh gillnet techniques, with nearly 60% of all presentations dealing with these topics. In contrast, the use of other active sampling gear, especially trawling and purse seining, received relatively little attention and still requires substantial further development. Reviews of standardization of fish sampling in the European Union, Russia and North America were also presented and clearly showed the benefits of standardized procedures. A number of contributions emphasized the need to use a combination of several methods for the same habitat. A true picture of the fish stock includes knowledge of the abundance, biomass, number of species, size and age compositions. Obtaining results of assured quality for all important lake and reservoir habitats and time periods still presents a significant challenge, although good progress is being made towards this important objective.
Asian Fisheries Science, Jul 21, 2010
Population dynamics of dominant fish species in two lowland reservoirs of Sri Lanka were studied ... more Population dynamics of dominant fish species in two lowland reservoirs of Sri Lanka were studied based on length-based stock assessment methodologies, as implemented in FiSAT II software. The estimated growth parameters of Oreochromis mossambicus in Udawalawe and Chandrikawewa reservoirs and those of O. niloticus and Labeo dussumieri in Udawalawe reservoir fall within the growth space of auximetric plots of cichlids and cyprinids indicating reliability of estimates. In the Chandrikawewa reservoir where O. mossambicus exhibited faster growth, increased fishing pressure might lead to push the population towards the extreme of 'rselected' life strategy so that continuation of the fishery at the present exploitation level is advisable. Relative yield-per-recruit (Y'/R) analyses indicate that for O. niloticus and L. dussumieri in Udawalawe reservoir, exploitation levels can be increased to optimize Y'/R. However, since these two species and O. mossambicus are caught in the same fishing gear, exploitation rate for O. niloticus and L. dussumieri has to be increased to a level that would not lead to over-exploitation of O. mossambicus stock.
Asian Fisheries Science, 2002
The fishery of a shallow irrigation reservoir in Sri Lanka was investigated. Catch and effort dat... more The fishery of a shallow irrigation reservoir in Sri Lanka was investigated. Catch and effort data of all species and length frequency data of cichlid species, O. mossambicus (Peters) and O. niloticus (L.) which form over 80% of landings, collected over a period of 13 months were analyzed. Yield-per-recruit analyses of the two cichlid species, performed using FiSAT computer software package indicated that both cichlid stocks in the reservoir are optimally exploited. Annual fish yield and monthly mean fishing intensity (FI in boat-days per month) were estimated for two scenarios, i.e., reservoir area at full supply level (FSL) and actual monthly mean reservoir area. They indicate that the estimates of yield (228 kg·ha-1 ·yr-1) and FI (2.9 boat-days·ha-1 ·month-1), which are computed for the reservoir area at FSL are about 23 and 21% respectively of the estimates of yield (985.5 kg·ha-1 ·yr-1) and FI (13.3 boat-days·ha-1 ·month-1) based on actual monthly mean reservoir area. Fish stock assessment and fisheries management strategies, which are based on Y and FI estimated on the basis of reservoir area at FSL are therefore bound to be inaccurate. Potential implications of difference of yield and FI estimates based on monthly mean reservoir area and area at FSL, in determining the optimal fishing strategies are discussed.
Sri Lanka Journal of Aquatic Sciences, 2016
INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary res... more INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary research program undertaken over the period 1998–2001. Three reservoirs in Sri Lanka (Victoria, Minneriya and Udawalawe) of different morphology, age and geographic location, Ubolratana reservoir, in Thailand, and Lake Taal, in the Philippines, are the object of this study. The scope of the project encompasses a comparison of the limnology, fisheries and socioeconomic aspects of local communities in order to determine whether the trophic characteristics and key ecosystem processes sustain the available fisheries, and to examine the ecological potential for increased fish production by intensive cage culture. The paper first presents integrated results on trophic state, trophic structure and food web relationships of different water bodies. The results demonstrate the importance of ecosystem-orientated analysis in order to optimise management strategies. The broad spectrum of Asian water bodies studied allows testing of a set of hypotheses on: 1) the control of the trophic state of lakes and reservoirs by geographic, climatic and morphometric conditions; 2) the significance of the structure of the fish assemblages (bio-geography, exotic species) on ecosystem processes; 3) bottom up versus top down control under Asian reservoir and lake conditions (in comparison to established concepts for water bodies in the temperate zone); and 4) the human impact and resilience of ecosystem processes and trophic conditions towards human impact.
The fishery of a shallow irrigation reservoir in Sri Lanka was investigated. Catch and effort dat... more The fishery of a shallow irrigation reservoir in Sri Lanka was investigated. Catch and effort data of all species and length frequency data of cichlid species, O. mossambicus (Peters) and O. niloticus (L.) which form over 80% of landings, collected over a period of 13 months were analyzed. Yield-per-recruit analyses of the two cichlid species, performed using FiSAT computer software package indicated that both cichlid stocks in the reservoir are optimally exploited. Annual fish yield and monthly mean fishing intensity (FI in boat-days per month) were estimated for two scenarios, i.e., reservoir area at full supply level (FSL) and actual monthly mean reservoir area. They indicate that the estimates of yield (228 kg·ha-1 ·yr-1) and FI (2.9 boat-days·ha-1 ·month-1), which are computed for the reservoir area at FSL are about 23 and 21% respectively of the estimates of yield (985.5 kg·ha-1 ·yr-1) and FI (13.3 boat-days·ha-1 ·month-1) based on actual monthly mean reservoir area. Fish stock assessment and fisheries management strategies, which are based on Y and FI estimated on the basis of reservoir area at FSL are therefore bound to be inaccurate. Potential implications of difference of yield and FI estimates based on monthly mean reservoir area and area at FSL, in determining the optimal fishing strategies are discussed.
The pleurocercoid stages of Ligula intestinalis (L.) were found in the body cavities of 333 among... more The pleurocercoid stages of Ligula intestinalis (L.) were found in the body cavities of 333 among the 1105 Amblypharyngodon melettinus (Valenciennes) examined from the Victoria Reservoir, Sri Lanka from January 1999 to January 2000. Mean prevalence of this parasite was 23.38%. Mean intensity of infection of L. intestinalis in A. melettinus was 1.006. Mean body condition (CF) of infected A. melettinus was 0.009991 that was significantly different from that of uninfected fish (CF = 0.010445; t = 2.03; p<0.05).The occurrence of this parasite in A. melettinus represents the first record of L. intestinalis in any freshwater fish of Sri Lanka.
The status of the fisheries of Udawalawe and Chandrikawewa, two reservoirs in the Walawe river ba... more The status of the fisheries of Udawalawe and Chandrikawewa, two reservoirs in the Walawe river basin of Sri Lanka was investigated along with an assessment of the potential role of fisheries societies in fisheries management. Higher annual fish yield was reported in Udawalawe (137.6 kg ha-1) than in Chandrikawewa (69.9 kg ha-1). In both reservoirs, catches of cyprinids (Labeo dussumieri and exotic carps such as Labeo rohita and Catla catla) showed a positive correlation with rainfall. The high fish yield in Udawalawe was mainly due to high seasonal catches of these cyprinids during rainy season. In Chandrikawewa, a major proportion of the landings was formed by Oreochromis mossambicus and O. niloticus. Being situated within a wildlife sanctuary, some regulatory measures are in force in Udawalawe such as limiting the fishing time, banning the use of harmful fishing methods and need for obtaining fishing licenses, which help control fishing pressure. However, fish vendors were influential in making management decisions in this reservoir. In Chandrikawewa on the other hand, it is possible to establish mechanisms for better involvement of resource users in decision-making. For effective management of the fisheries of the two reservoirs, a strong fisheries extension mechanism is needed through which reservoir fishing communities could be motivated to establish institutions and mechanisms for achieving consensus among fishers which can be treated as platforms for resource use negotiation.
Sri Lanka Journal of Aquatic Sciences, 2016
The grey mullets (Family: Mugilidae) have been described as plankton feeders, herbivores, omnivor... more The grey mullets (Family: Mugilidae) have been described as plankton feeders, herbivores, omnivores, slime feeders, foul feeders, bottom feeders, etc. In general, grey mullets are known to be benthic feeders. During a comprehensive trophic ecological study of fish assemblages in brush-parks in the Negombo estuary, Sri Lanka, carried out from 2014 to 2016, a food item that was not found in the aquatic environment, such as zooplankton, phytoplankton, macrophyte or detritus, was observed in the gut contents of mugilids. In this communication, the authors report that the frequency of occurrence of these peculiar items in the gut contents were shedded gill epithelia. Even though shedded gill epithelia were not considered as a food item, they were the most common item in the stomach contents contributing to 49.9% of the mean volume of stomach contents.
Asian Fisheries Science
Growth and mortality were estimated from the length-frequency data of Oreochromis mossambicus fro... more Growth and mortality were estimated from the length-frequency data of Oreochromis mossambicus from the gillnet fishery of Parakrama Samudra, a manmade lake in Sri Lanka, separately for its three basins. The asymptotic length (L_) and the growth constant (K) of 0. mossambicus in the northern basin of the lake (34.9 cm and 0.3, respectively) are appreciably different from those in other two basins (middle basin, L.. = 38.8 cm and K = 0.24; southern basin, L.. = 40.6 cm and K = 0.22). Total mortality rates in the northern, middle and southern basins are 2.22, 1.64 and 1.07, respectively. The spatial differences in growth are suggested to be due to different fishing pressure and environmental conditions. Yield-per-recruit analyses indicate that in the populations with low I.._ and high K, exploitation level should be maintained at a low level. Fish yield could be optimized by increasing the size of first capture and exploitation rate in the populations with high L.. and low K.
Participation of community groups is one of the main requirements for culture-based fisheries (CB... more Participation of community groups is one of the main requirements for culture-based fisheries (CBF) in non-perennial reservoirs of Sri Lanka. Homogeneity of the group characteristics facilitates to arrive at collective decisions. And as such can be considered as positive feature for development of CBF. In this paper an attention made to identify the most important social and economic characteristics affecting the group decisions for development and management of CBF in non-perennial reservoirs of Sri Lanka. Principal component analysis (PCA) revealed that out of 25 measured parameters only 4 namely, the group size of fishers, participation rate in fisheries activities, caste of community and participation rate for regular meetings, were important in determining socioeconomic heterogeneity of the sample. Average income derived from CBF was appreciably high in communities with small group size and high participatory level in-group activities. Contingent evaluation of willingness to pay also demonstrated that the involvement of more people with fishing attitude would be preferred for the successful CBF activities. This analysis indicates that socioeconomic characteristics of rural communities can be meaningfully used for selecting non-perennial reservoirs suitable for development of CBF in Sri Lanka.
Fisheries Research, 2009
The conference 'Fish Stock Assessment Methods for Lakes and Reservoirs: Towards the True Picture ... more The conference 'Fish Stock Assessment Methods for Lakes and Reservoirs: Towards the True Picture of Fish Stock' (FSAMLR) was held in September 2007 in Ceske Budejovice, Czech Republic. A total of 110 participants from 34 countries attended the meeting and 93 lectures were presented. Great advances were reported in fish surveys using hydroacoustics and multimesh gillnet techniques, with nearly 60% of all presentations dealing with these topics. In contrast, the use of other active sampling gear, especially trawling and purse seining, received relatively little attention and still requires substantial further development. Reviews of standardization of fish sampling in the European Union, Russia and North America were also presented and clearly showed the benefits of standardized procedures. A number of contributions emphasized the need to use a combination of several methods for the same habitat. A true picture of the fish stock includes knowledge of the abundance, biomass, number of species, size and age compositions. Obtaining results of assured quality for all important lake and reservoir habitats and time periods still presents a significant challenge, although good progress is being made towards this important objective.
Asian Fisheries Science, Jul 21, 2010
Population dynamics of dominant fish species in two lowland reservoirs of Sri Lanka were studied ... more Population dynamics of dominant fish species in two lowland reservoirs of Sri Lanka were studied based on length-based stock assessment methodologies, as implemented in FiSAT II software. The estimated growth parameters of Oreochromis mossambicus in Udawalawe and Chandrikawewa reservoirs and those of O. niloticus and Labeo dussumieri in Udawalawe reservoir fall within the growth space of auximetric plots of cichlids and cyprinids indicating reliability of estimates. In the Chandrikawewa reservoir where O. mossambicus exhibited faster growth, increased fishing pressure might lead to push the population towards the extreme of 'rselected' life strategy so that continuation of the fishery at the present exploitation level is advisable. Relative yield-per-recruit (Y'/R) analyses indicate that for O. niloticus and L. dussumieri in Udawalawe reservoir, exploitation levels can be increased to optimize Y'/R. However, since these two species and O. mossambicus are caught in the same fishing gear, exploitation rate for O. niloticus and L. dussumieri has to be increased to a level that would not lead to over-exploitation of O. mossambicus stock.
Asian Fisheries Science, 2002
The fishery of a shallow irrigation reservoir in Sri Lanka was investigated. Catch and effort dat... more The fishery of a shallow irrigation reservoir in Sri Lanka was investigated. Catch and effort data of all species and length frequency data of cichlid species, O. mossambicus (Peters) and O. niloticus (L.) which form over 80% of landings, collected over a period of 13 months were analyzed. Yield-per-recruit analyses of the two cichlid species, performed using FiSAT computer software package indicated that both cichlid stocks in the reservoir are optimally exploited. Annual fish yield and monthly mean fishing intensity (FI in boat-days per month) were estimated for two scenarios, i.e., reservoir area at full supply level (FSL) and actual monthly mean reservoir area. They indicate that the estimates of yield (228 kg·ha-1 ·yr-1) and FI (2.9 boat-days·ha-1 ·month-1), which are computed for the reservoir area at FSL are about 23 and 21% respectively of the estimates of yield (985.5 kg·ha-1 ·yr-1) and FI (13.3 boat-days·ha-1 ·month-1) based on actual monthly mean reservoir area. Fish stock assessment and fisheries management strategies, which are based on Y and FI estimated on the basis of reservoir area at FSL are therefore bound to be inaccurate. Potential implications of difference of yield and FI estimates based on monthly mean reservoir area and area at FSL, in determining the optimal fishing strategies are discussed.
Sri Lanka Journal of Aquatic Sciences, 2016
INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary res... more INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary research program undertaken over the period 1998–2001. Three reservoirs in Sri Lanka (Victoria, Minneriya and Udawalawe) of different morphology, age and geographic location, Ubolratana reservoir, in Thailand, and Lake Taal, in the Philippines, are the object of this study. The scope of the project encompasses a comparison of the limnology, fisheries and socioeconomic aspects of local communities in order to determine whether the trophic characteristics and key ecosystem processes sustain the available fisheries, and to examine the ecological potential for increased fish production by intensive cage culture. The paper first presents integrated results on trophic state, trophic structure and food web relationships of different water bodies. The results demonstrate the importance of ecosystem-orientated analysis in order to optimise management strategies. The broad spectrum of Asian water bodies studied allows testing of a set of hypotheses on: 1) the control of the trophic state of lakes and reservoirs by geographic, climatic and morphometric conditions; 2) the significance of the structure of the fish assemblages (bio-geography, exotic species) on ecosystem processes; 3) bottom up versus top down control under Asian reservoir and lake conditions (in comparison to established concepts for water bodies in the temperate zone); and 4) the human impact and resilience of ecosystem processes and trophic conditions towards human impact.
The fishery of a shallow irrigation reservoir in Sri Lanka was investigated. Catch and effort dat... more The fishery of a shallow irrigation reservoir in Sri Lanka was investigated. Catch and effort data of all species and length frequency data of cichlid species, O. mossambicus (Peters) and O. niloticus (L.) which form over 80% of landings, collected over a period of 13 months were analyzed. Yield-per-recruit analyses of the two cichlid species, performed using FiSAT computer software package indicated that both cichlid stocks in the reservoir are optimally exploited. Annual fish yield and monthly mean fishing intensity (FI in boat-days per month) were estimated for two scenarios, i.e., reservoir area at full supply level (FSL) and actual monthly mean reservoir area. They indicate that the estimates of yield (228 kg·ha-1 ·yr-1) and FI (2.9 boat-days·ha-1 ·month-1), which are computed for the reservoir area at FSL are about 23 and 21% respectively of the estimates of yield (985.5 kg·ha-1 ·yr-1) and FI (13.3 boat-days·ha-1 ·month-1) based on actual monthly mean reservoir area. Fish stock assessment and fisheries management strategies, which are based on Y and FI estimated on the basis of reservoir area at FSL are therefore bound to be inaccurate. Potential implications of difference of yield and FI estimates based on monthly mean reservoir area and area at FSL, in determining the optimal fishing strategies are discussed.
The pleurocercoid stages of Ligula intestinalis (L.) were found in the body cavities of 333 among... more The pleurocercoid stages of Ligula intestinalis (L.) were found in the body cavities of 333 among the 1105 Amblypharyngodon melettinus (Valenciennes) examined from the Victoria Reservoir, Sri Lanka from January 1999 to January 2000. Mean prevalence of this parasite was 23.38%. Mean intensity of infection of L. intestinalis in A. melettinus was 1.006. Mean body condition (CF) of infected A. melettinus was 0.009991 that was significantly different from that of uninfected fish (CF = 0.010445; t = 2.03; p<0.05).The occurrence of this parasite in A. melettinus represents the first record of L. intestinalis in any freshwater fish of Sri Lanka.
The status of the fisheries of Udawalawe and Chandrikawewa, two reservoirs in the Walawe river ba... more The status of the fisheries of Udawalawe and Chandrikawewa, two reservoirs in the Walawe river basin of Sri Lanka was investigated along with an assessment of the potential role of fisheries societies in fisheries management. Higher annual fish yield was reported in Udawalawe (137.6 kg ha-1) than in Chandrikawewa (69.9 kg ha-1). In both reservoirs, catches of cyprinids (Labeo dussumieri and exotic carps such as Labeo rohita and Catla catla) showed a positive correlation with rainfall. The high fish yield in Udawalawe was mainly due to high seasonal catches of these cyprinids during rainy season. In Chandrikawewa, a major proportion of the landings was formed by Oreochromis mossambicus and O. niloticus. Being situated within a wildlife sanctuary, some regulatory measures are in force in Udawalawe such as limiting the fishing time, banning the use of harmful fishing methods and need for obtaining fishing licenses, which help control fishing pressure. However, fish vendors were influential in making management decisions in this reservoir. In Chandrikawewa on the other hand, it is possible to establish mechanisms for better involvement of resource users in decision-making. For effective management of the fisheries of the two reservoirs, a strong fisheries extension mechanism is needed through which reservoir fishing communities could be motivated to establish institutions and mechanisms for achieving consensus among fishers which can be treated as platforms for resource use negotiation.