Sri Lankan reservoir fishery: a case for introduction of a co-management strategy

The inland fisheries of Sri Lanka are essentially artisanal on most of the reservoirs in the country. The annual inland fish production declined dramatically after 1990, when state patronage for the development of the inland fisheries was discontinued for 4 years. This decline was shown to be a result of growth overfishing of the two dominant cichlid species which accounted for over 90% of landings. This was a result of using small mesh ( < 6.9 cm) gillnets in the absence of the State-sponsored monitoring procedure in the fishery after 1990. This indicates that it is necessary to monitor inland fisheries management in Sri Lanka through a centralized authority in the current situation. However, in some Sri Lankan reservoirs, fishing communities can be categorized as 'organized' because they collectively make decisions to define procedures for the rational exploitation of the fishery resources. In reservoirs with 'organized' fishing, the communities themselves have developed mechanisms to regulate the landing sizes of dominant cichlid fish species through community-based fisheries management strategies. In such reservoirs, over-exploitation of fish stocks was not evident, even after 1990, when state-sponsored monitoring procedures were suspended. Based on these observations, an alternative approach is recommended for the management of Sri Lankan reservoir capture fisheries in which the Government and resource-users have equal responsibilities in the management of the resources.     

Yield predictive models for Sri Lankan reservoir fisheries

Tropical reservoirs are primarily constructed for irrigation, generation of hydroelectricity and water supply schemes. Development of inland fisheries is a secondary use of most reservoirs. In Sri Lanka, most reservoirs are scattered in the rural areas of the country so that investigation of the fisheries of individual reservoirs with a view to developing management plans is prohibitive. The present study was instigated to explore the possibilities of developing suitable yield predictive models, which can be used in developing management strategies for the Sri Lankan reservoirs. The study was carried out in 11 perennial reservoirs of Sri Lanka. Basic limnological parameters (conductivity, dissolved phosphorus, total phosphorus, chlorophyll a [chl a] content and alkalinity) were determined in each of these reservoirs. Daily data on fish catch and fishing effort were collected in each reservoir. Data on catchment areas (CA), reservoir area (RA) and reservoir capacity (RC) were obtained from the irrigation and survey departments. It is evident that chl a is positively influenced by nutrients (dissolved phosphorus and total phosphorus), morphoedaphic indices derived as alkalinity to mean depth (MEIa) and conductivity to mean depth (MEIc) ratios and CA/RC ratios. MEIa and MEIc are also positively influenced by CA/RC ratios. All these morphological and edaphic parameters were found to positively influence fish yield in reservoirs. As fishing intensity (FI) is also a major determinant of fish yields, fish yield was better accounted by multiple regression models in which FI and individual morphological and edaphic parameters were used as independent variables. Of these multiple regression relationships, the best predictive power for fish yield (Y in kg ha?1 yr?1) was found by Y=18.9+6.78 FI+0.0073 CA/RC where FI is expressed as boat‐days ha?1 yr?1 and CA and RC are in km2 and km3, respectively. In this relationship, FI and CA/RC account for about 68% of the variation in fish yield.     

Status of the introduced cichlid Sarotherodon mossambicus (Peters) in the reservoir fishery of Sri Lanka: a management strategy and ecological implications

Abstract. The inland fishery in Sri Lanka (6–10°N; 79–82°E) is essentially a fishery confined to man-made lakes and is dominated by the introduced cichlid Sarotherodon mossambicus (Peters). Catch statistics of 20 such major reservoirs indicate that the yield of this species ranges from 64·0 to 918 kg per ha and accounts for between 56 and 99% of the total yield in individual reservoirs. The yield of S. mossambicus is closely related to the fishing pressure exerted. Catch/effort data from the individual reservoir fisheries when analysed collectively simulate changes in a single large fishery. In the fishery the relationship of yield to effort is described by the equation: Y = 4·OX – 53·8X ( r = 0·92; P < 0·001), where Y = yield in kg per ha per annum and X = number of craft-days per ha per annum, indicating that the reservoirs in Sri Lanka remain underfished. However, very high increases in fishing pressure in two reservoirs, for which data are available over a 5-year period, indicate that the increases have resulted in a significant decline in the catch per unit effort. The reasons for the success of the S. mossambicus fishery in individual reservoirs, and also simulation of features of a single large fishery in reservoirs, with widely different hydrological and limnological regimes, are discussed in qualitative terms. It is hypothesized that the abundance is determined by factors other than food availability. Fresh management strategies to optimize the fishery from the point of view of optimal fishing pressure permissible from the present analysis are suggested.     

Impact of Oreochromis mossambicus × O. niloticus (Pisces: Cichlidae) hybridization on population reproductive potential and long-term influence on a reservoir fishery

Abstract Exotic cichlids, introduced to Asia during the second half of the twentieth century, contribute significantly to the reservoir fisheries in the region. The two major cichlid species, Oreochromis mossambicus (Peters) and O. niloticus (L.), tend to interbreed easily. In Sri Lankan reservoirs, introgressive hybridization of these two cichlids takes place. The reproductive biology of O. mossambicus, O. niloticus and their hybrids in three reservoirs in Sri Lanka was evaluated. An imbalance in sex ratio with male dominance was evident. The estimated fecundity for 20-cm fish, using fecundity-total length relationships for various populations, indicated that there was a decline in fecundity in hybrid forms. It is hypothesized that the long-term effect of crosshybridization between the two cichlids might lead to a decline in fish yields in perennial reservoirs of Sri Lanka. The importance of the findings of the present study for the management of the reservoir fisheries in Asia is highlighted.     

Efficiency of culture-based fisheries production in village irrigation systems of Sri Lanka

Despite the growing popularity of culture-based fisheries (CBFs) associated with village irrigation systems (VISs) in Sri Lanka, there is less knowledge about factors that influence productivity levels. CBFs compete with rice for access to water in the VIS, so maximizing the efficiency of CBFs is essential to ensure that the limited water resources are used most effectively. To address this, primary data from 325 fish farming groups were used to estimate a stochastic translog production frontier. Technical efficiency in these irrigation systems was found to be generally low, and substantially lower than that of other aquaculture production systems in other Asian countries. This suggests that production can be increased substantially with better management using existing technology and resources. Removing subsidies, improving consultation with extension officials and improving water user rights – in particular, the introduction of a transferable community quota system – were found to be key means for improving efficiency.     

EVALUATION OF COMMUNITY PARTICIPATION FOR THE DEVELOPMENT OF CULTURE-BASED FISHERIES IN VILLAGE RESERVOIRS OF SRI LANKA

In this paper, an attempt is made to identify the socioeconomic characteristics of a community that influence the development and management of culture-based fisheries in village reservoirs of Sri Lanka. Socioeconomic data were collected from 46 agricultural farming communities associated with 47 village reservoirs in Sri Lanka. Principal component analysis indicated that scores of the first principal component were positively influenced by socioeconomic characteristics that are favorable for making collective decisions. These included leadership of the officers, age of the group, percentage of active members of the group, percentage of kinship of the group, percentage of common interest of the group, and percentage of participation of the group. The size of the group had a negative effect on the first principal component. The principal component scores of communities were positively related to willingness to pay (P < 0.001). The communities with socioeconomic characteristics favoring collective decision making were in favor of culture-based fisheries. Homogeneity of group characteristics facilitated successful development of culture-based fisheries.     

Culture-based fisheries in non-perennial reservoirs in Sri Lanka: production and relative performance of stocked species

Abstract In Sri Lanka, there is a great potential for the development of culture-based fisheries because of the availability of around 12 000 non-perennial reservoirs in the dry zone (<187 cm annual rainfall) of the island. These reservoirs fill during the north-east monsoonal period in October to December and almost completely dry up during August to October. As these non-perennial reservoirs are highly productive, hatchery-reared fish fingerlings can be stocked to develop culture-based fisheries during the water retention period of 7–9 months. The present study was conducted in 32 non-perennial reservoirs in five administrative districts in Sri Lanka. These reservoirs were stocked with fingerlings of Indian (catla Catla catla Hamilton and rohu Labeo rohita Hamilton) and Chinese (bighead carp Aristichthys nobilis Richardson) major carps, common carp Cyprinus carpio L., genetically improved farmed tilapia (GIFT) strain of Nile tilapia, Oreochromis niloticus (L.) and post-larvae of giant freshwater prawn, Macrobrachium rosenbergii De Man, at three different species combinations and overall stocking densities (SD) ranging from 218 to 3902 fingerlings ha⁻¹, during the 2002–2003 culture cycle. Of the 32 reservoirs stocked, reliable data on harvest were obtained from 25 reservoirs. Fish yield ranged from 53 to 1801 kg ha⁻¹ and the yields of non-perennial reservoirs in southern region were significantly (P < 0.05) higher than those in the northern region. Naturally-recruited snakehead species contributed the catches in northern reservoirs. Fish yield was curvilinearly related to reservoir area (P < 0.05), and a negative second order relationship was evident between SD and yield (P < 0.05). Chlorophyll-a and fish yield exhibited a positive second order relationship (P < 0.01). Bighead carp yield impacted positively on the total yield (P < 0.05), whereas snakehead yield impact was negative. Bighead carp, common carp and rohu appear suitable for poly-culture in non-perennial reservoirs. GIFT strain O. niloticus had the lowest specific growth rate among stocked species and freshwater prawn had a low return.     

Use of geographical information systems as a tool for predicting fish yield in tropical reservoirs: case study on Sri Lankan reservoirs

Use of geographical information systems (GIS) in inland fisheries has hitherto been essentially restricted to site evaluation for aquaculture development and assessment of limnological changes in time and space in individual water bodies. The present GIS study was conducted on the land-use pattern of the catchments of nine reservoirs in Sri Lanka, for which detailed fishery data, viz. yield, fishing intensity, landing size of major constituent species, together with selected limnological data such as conductivity and chlorophyll- a , were available. Potential statistical relationships (linear, curvilinear, exponential and second-order polynomial) of fish yield ( FY , in kg ha⁻¹ yr⁻¹) to different land-use patterns, such as forest cover ( FC , in km²) and shrub-land ( SL , in km²), either singly, or in combination, and/or the ratio of each land type to reservoir area ( RA in km²) and reservoir capacity ( RC in km³), were explored. Highly significant relationships were evident between FY to the ratio of SL and/or FC + SL to RA and/or RC . Similarly, the above land-use types to RA and RC ratios were significantly related to limnological features of the reservoirs. The relationships of FY to various parameters obtained in this study were much better correlated than those relationships of FY to limnological and biological parameters used in yield prediction in tropical and temperate lacustrine waters previously.     

Notes on the occurrence of two tropical species of Anguilla in reservoirs in south-eastern Sri Lanka and preliminary data on the populations

Abstract. The occurrence and abundance of eels were investigated in five lowland reservoirs in south-eastern Sri Lanka. Paired fyke nets and longlines were used for sampling eels. Two tropical species of eel. Anguilla bicolor McClelland and Anguilla nebulosa McClelland, were caught. In two of the five reservoirs investigated only A. bicolor was found and in another two reservoirs both species were caught. Eels seemed to be absent from one reservoir. The CPUE in reservoirs with eel was between 0·13 and 2·60 eels of both species per fyke net and night, and the total weight was between 81 and 814g. A small capture-recapture experiment in Badagiriya, where eels seemed to be most plenliful, gave a population estimate of only six eels or 1·2 kg per ha (eels longer than 40cm). Such a low abundance was regarded as unrealistic. Stocks of eel could presumably, at least in some reservoirs, withstand commercial exploitation but more information is needed on recruitment, growth and migration before any advice can be given on the management of stocks.     

Biochemical evidence of hybrid gene introgression in some reservoir populations of tilapia in southern Sri Lanka

Abstract. Two species of tilapia, Oreochromis mossambicus (Peters) and O. niloticus (L.), from five reservoirs in southern Sri Lanka as well as fish from a fish hatchery and laboratory stock were studied by starch gel electrophoresis at 18 enzyme loci, to determine the degree of mixing of the two species. Two reservoirs showed little or no mixing between O. mossambicus and O. niloticus , while two other reservoirs as well as the hatchery stock showed a high degree of mixing of the two species. The laboratory stock of O. niloticus also showed introgression of O. mossambicus alleles. The similarities of the local stocks to the original African as well as other Asian stocks is discussed.     

Ornamental Fish Industry in Sri Lanka: Present Status and Future Trends

The aquarium fish industry in Sri Lanka has become a valuable foreign exchange earner during the past few years, earning Rs. 530 million in 1998. Sri Lankan ornamental fish exports for the international market include locally wild caught marine, brackish-water and freshwater species as well as captive bred freshwater fish. Presently, there are about 18 registered aquarium fish exporters and together they currently contribute approximately 1% of the world's demand for ornamental fish. Of the freshwater fish species exported from Sri Lanka, the guppy ranks the highest (67% by number), followed by swordtails, angels, platies and various species of tetras. This study aims to assess the present status and future trends in the ornamental fish industry in Sri Lanka; to overview the present fish production system which caters for the international market; and to identify present constraints within the industry. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evaluation of the robustness of predictive yield models based on catchment characteristics using GIS for reservoir fisheries in Sri Lanka

Land-use patterns in the catchment areas of Sri Lankan reservoirs, which were quantified using Geographical Information Systems (GIS), were used to develop quantitative models for yield prediction. The validity of these models was evaluated through the application to five reservoirs that were not used in the development of the models, and by comparing with the actual fish yield data of these reservoirs collected by an independent body. The robustness of the predictive models developed was tested by principal component analysis (PCA) on limnological characteristics, land-use patterns of the catchments and fish yields. The predicted fish yields in five Sri Lankan reservoirs, using the empirical models based on the ratios of forest cover and/or shrub cover to reservoir capacity or reservoir area were in close agreement with the observed fish yields. The scores of PCA ordination of productivity-related limnological parameters and those of land-use patterns were linearly related to fish yields. The relationship between the PCA scores of limnological characteristics and land-use types had the appropriate algebraic form, which substantiates the influence of the limnological factors and land-use types on reservoir fish yields. It is suggested that the relatively high predictive power of the models developed on the basis of GIS methodologies can be used for more accurate assessment of reservoir fisheries. The study supports the importance and the need for an integrated management strategy for the whole watershed to enhance fish yields.     

Putting the fish into inland fisheries – A global allocation of historic inland fish catch

Inland waters support the livelihoods of up to 820 million people and provide fisheries that make an essential contribution towards food security, particularly in the developing world where 90% of inland fisheries catch is consumed. Despite their importance, inland fisheries are overlooked in favour of other water use sectors deemed more economically important. Inland fisheries are also driven by external factors such as climate change and habitat loss, which impedes our ability to manage them sustainably. Using a river basin approach to allocate fish catch, we have provided an integrated picture of how different inland water bodies contribute to global inland fisheries catches. There is a substantial amount of information available on inland fisheries, but it has never been synthesised to build this global picture. Fishery statistics from river basins, lakes, floodplains, hydrobasins, and countries covering a time span from 1960–2018 were analysed. Collation of basin-scale fisheries statistics suggests a global inland catch of ≈17.4 million tonnes (PSE = ±3.93 million tonnes) in 2010, considerably more than the 10.8 million tonnes published by the United Nations Food and Agriculture Organization (FAO), but in line with estimates based on household consumption. The figure is considered a likely maximum due to recent reductions in catches because of closures, threats, and fisheries declines in the most productive fisheries. It is recommended that sentinel fisheries, which are important for food provision, employment, or where threats facing a fishery could cause a deterioration in catch, are identified to provide the baseline for a global monitoring programme.     

贵贵州地区碳汇渔业潜力研究

我国是当今世界水产品产量最高的国家，渔业呈现地区发展不平衡、不充分的格局，内陆地区渔业发展水平总体上远低于沿海地区。在当前“碳达峰”和“碳中和”双碳战略背景下，渔业迎来了前所未有的机遇和挑战尤其是对于内陆淡水渔业，碳汇渔业将成为未来的一个重要发展方向。该文主要根据《中国水产统计资料》和《中国渔业统计年鉴》，以贵州省为例，结合贵州地区近年来的渔业发展现状，估算了贵州省近五年(2016—2020年)的渔业碳汇强度，分析了贵州地区发展碳汇渔业的潜力。渔业碳汇强度估算结果显示，2016—2020年贵州省渔业碳移出量在1.4 t到1.7 t之间，平均碳移出量为1.5 t。贵州省渔业发展相对落后，水产品捕捞产量和养殖产量均远低于全国平均水平，但贵州省近年来大力推广稻渔综合种养和湖库养殖等生态渔业模式，到2020年稻田养殖和湖库养殖面积分别占全省水产养植总面积的74.2%和19.2%，二者产量达到全省总产量的一半以上，远高于全国平均水平。稻渔综合种养和湖库养殖等生态渔业成为贵州省水产养殖业的重要养殖模式，未来这类具备碳汇功能的生态渔业规模将会进一步扩大，是贵州地区扭转渔业养殖模式和渔业经济增长方式的机遇，对碳汇渔业的全面推广和渔业的可持续发展具有重要指导意义。     

Why have global shark and ray landings declined: improved management or overfishing?

Global chondrichthyan (shark, ray, skate and chimaera) landings, reported to the United Nations Food and Agriculture Organization (FAO), peaked in 2003 and in the decade since have declined by almost 20%. In the FAO's 2012 ‘State of the World's Fisheries and Aquaculture’ report, the authors ‘hoped’ the reductions in landings were partially due to management implementation rather than population decline. Here, we tested their hypothesis. Post‐peak chondrichthyan landings trajectories from 126 countries were modelled against seven indirect and direct fishing pressure measures and eleven measures of fisheries management performance, while accounting for ecosystem attributes. We found the recent improvement in international or national fisheries management was not yet strong enough to account for the recent decline in chondrichthyan landings. Instead, the landings declines were more closely related to fishing pressure and ecosystem attribute measures. Countries with the greatest declines had high human coastal population sizes or high shark and ray meat exports such as Pakistan, Sri Lanka and Thailand. While important progress had been made, country‐level fisheries management measures did not yet have the strength or coverage to halt overfishing and avert population declines of chondrichthyans. Increased implementation of legally binding operational fisheries management and species‐specific reporting is urgently required to avoid declines and ensure fisheries sustainability and food security.     

Review of trends in the development of European inland aquaculture linkages with fisheries

Aquaculture is a multifaceted, dynamic food production sector in Europe. The average annual growth rate of aquaculture production in Western Europe was 5.5% between 1988 and 1998, while in Eastern Europe production declined by 56% during the same period. The main growth in aquaculture production has taken place in the marine environment, particularly in the expanding salmon, Salmo salar L., industry of Northern Europe. Inland aquaculture only contributed 19% of the total aquaculture production in 1998. Trout in Western Europe, and common carp, Cyprinus carpio L., in Eastern Europe are the dominant species in inland aquaculture. Inland fisheries production has been stagnant in Western Europe and has declined considerably in Eastern Europe. The importance of recreational fisheries is increasing all over Europe, although no reliable data are available on angler catches. The major interactions between aquaculture and fisheries are pollution by untreated effluents from farms and impacts on indigenous fish stocks. The conflict is decreasing as more advanced systems are used in inland aquaculture, including water recirculation and effluent treatment. The positive benefit of aquaculture is that the sector supports extensive stocking programmes in commercial and recreational fisheries all over Europe.     

Culture-based fisheries in non-perennial reservoirs of Sri Lanka: influence of reservoir morphometry and stocking density on yield

Abstract  Culture-based fish yield in non-perennial reservoirs of Sri Lanka was related to reservoir morphometry and stocking density. The reservoirs were stocked mainly with fingerlings of one Chinese and three Indian major carp species, common carp, Cyprinus carpio L., and the genetically improved farmed tilapia strain of Nile tilapia, Oreochromis niloticus (L.), at four pre-determined species combinations and a range of stocking densities [ SD (fingerlings ha⁻¹)]. Twenty-three reservoirs were harvested successfully at the end of the culture period of 2002–2003. Basic limnological and morphometric parameters, including shoreline development ( D _L ) and shoreline area ratio ( R _LA ), were estimated for each of the 23 reservoirs. Bray–Curtis similarity and non-metric multidimensional scaling using mean values of limnological data revealed that reservoirs could be ordinated into two major clusters, one with intact sample distribution due to similar trophic characteristics and the other with scattered sample distribution. Reservoirs in the cluster with similar trophic characteristics showed significant correlation ( P  < 0.05) between R _LA and total fish yield ( Y ). A multiple regression equation, Y  = −693 + 4810  R _LA  + 0.484 SD , was generated to estimate fish harvest in relation to SD .     

A fresh look at inland fisheries and their role in food security and livelihoods

The role of inland fisheries in livelihoods, food security and sustainable development is often overshadowed by the higher profile interest in ocean issues. Whilst inland fisheries' catch and contribution to global nutrition, food security and the economy, are less than that of marine fisheries, global‐level comparisons of fish production obscure considerable livelihood impacts in certain countries and sub‐national areas. To highlight these contributions, this paper synthesizes recent data and innovative approaches for assessing such livelihood contributions and their importance in countries with limited access to ocean resources and aquaculture. Inland fisheries are crucial for many socially, economically and nutritionally vulnerable groups of people around the world, but the challenges in monitoring inland fisheries preclude a complete understanding of the magnitude of their contributions. This situation is rapidly improving with increasing recognition of inland fisheries in development discourses, which has also encouraged research to enhance knowledge on the importance of inland fisheries. We review this work, including collated information published in a recent Food and Agriculture Organization report, to provide an up to date characterization of the state of knowledge on the role of inland fisheries.     

Factors contributing to the outcome of stocking programmes in Cuban reserviors

Abstract In less-developed countries, fisheries enhancement using stocking is a common practice to manage reservoirs for biomass production. In many cases, there appears to be little control over whether the stocking activity is appropriate or necessary. Cuban reservoir fisheries have been usually managed to maximize fish biomass. Blue tilapia have been introduced and supplemented in reservoirs, and Chinese carp are introduced and maintained in reservoirs throughout the entire island. Supplemental stocking with introduced fish species is a usual practice to manage large and medium-sized reservoirs. Small and very small reservoirs have been managed as semi-intensively enhanced fisheries with carp and tilapia stocking. The main purposes of the present paper are to study the factors contributing to the outcome of stocking programmes in reservoirs and to test the hypotheses that supplementary stocking for self-sustained fish populations usually cannot contribute to increase fish yield. Yield and stocking data by groups of fish species were available for Cuban reservoirs. Total fish yield was only slightly related to total fish stocking density for the complete set of reservoirs. However, this result was mainly because of the relationship between total yield and cyprinid stocking for semi-intensively-used reservoirs. Tilapia yield was not significantly related to tilapia stocking for both extensively and semi-intensively-used reservoirs. However, yield and stocking for cyprinids were highly related for both reservoir subsets. Therefore, cyprinid stocking was effective in certain reservoirs, but tilapia stocking was not effective in any reservoir. Moreover, tilapia stocking was a superfluous activity for reservoirs where tilapia have an adequate natural reproduction cycle.     

Regional socio-economic importance of fisheries in Finland

The total value of Finnish fisheries production in 1997 was almost FIM 2 billion. The bulk of this sum was from processing and wholesaling, but in terms of value added, somewhat more than half was contributed by the primary sector, i.e. fishing and fish farming. In economic terms, fisheries accounted for 0.1% of gross domestic product (GDP) in 1997 and the relative job creation capacity was 0.15%. This paper examines the structure of Finnish fisheries in terms of production value and employment. It also considers the level of dependency on fisheries and of value added along the production chain. The focus is on concentration of the industry and on input to the economy at the regional level. The concentration of fisheries and regional dependence on fisheries are assessed in absolute and relative terms. Examining employment and value added in these two ways enables the regional nature of fisheries to be shown in greater detail. The input of fisheries to the regional economy is examined by the share of value added and by location quotients. The location quotient compares an area's share of a particular activity with that area's share of some basic or aggregated phenomenon. The location quotient showed that fisheries have importance not only in the coastal area but also inland.