Habitat alterations and fragmentation caused by anthropogenic modifications of the riverine landscape have affected fish biodiversity by reducing the number of fish species. Fish are a major element of the aquatic environment, and they play an important role in maintaining ecosystem resilience. However, an incomplete understanding of links between river ecosystem functions and processes with fisheries is one of the major reasons for the alarming rate of decline of fish species. Recognizing the ecosystem services generated by fish populations is essential and is one step toward comprehensive, ecosystem-based management of riverine fisheries. Therefore, this paper is motivated by the need to explore the dimensions of fisheries as an ecosystem service. The data was collected from primary field observations and checklist-based key informant interviews at the seventeen fishing sites selected across an 800 km river stretch of the river. In addition, two focused group discussions with fishers at two sampling sites were held to provide first-hand knowledge of ecosystem services generated by fisheries. At first, the role of fisheries in generating ecosystem services for riverine ecosystem functioning and human demands is outlined using the Millennium Ecosystem Assessment approach. Then, the findings of a survey carried out from the headwaters to the delta of the Cauvery river are presented detailing the fisheries provisioning services, livelihoods, and other ecosystem services. The findings showed that the provisioning and cultural services are highly represented among the four categories of ecosystem services identified by the Millennium Ecosystem Assessment. However, in the literature reviewed, supporting, and regulating services are not well-represented. Based on these findings, the applicability of the ecosystem service concept can be elaborated to inform researchers and policymakers to enhance conservation efforts for fisheries.

Study region: Upper Cauvery river basin, India Study focus: Reservoir construction is one of the major contributors to changes in natural river flow regime characteristics. This study aims to understand the hydrological alterations resulting from the construction of reservoirs and water abstraction in the upper regions of the basin. The impacts of dams on river flow regimes where data is available only for periods after the construction of the dams is assessed. A landscape-based hydrological model, FLEX-Topo, is used to model the flows contributed by the upstream and downstream areas of four major reservoirs in the study area. A separate reservoir operation model is developed for each of the reservoirs. Next, the hydrological model is integrated with the reservoir model and the modelled flow at the downstream streamflow gauging station of each of the corresponding four sub-basins is calibrated. The modelled flow regimes with and without reservoirs are then compared using the indicators of hydrological alterations to understand the degree to which the flows have been altered by the reservoirs. New hydrological insights for the region: The results indicate that flow regimes have been modified from their natural state following reservoir impoundment and water abstractions. Significant impacts are observed in median monthly flow, 1-day minimum flow and low pulses. Such information could provide a reference to water managers to replicate the natural flow regimes, help sustain natural biota and thus contribute toward the sustainable management of river basins in India.

The process of development has led to the modification of river landscapes. This has created imbalances between ecological, economic, and socio-cultural uses of ecosystem services (ESs), threatening the biotic and social integrity of rivers. Anthropogenic modifications influence river landscapes on multiple scales, which impact river-flow regimes and thus the production of river ESs. Despite progress in developing approaches for the valuation ecosystem goods and services, the ecosystem service research fails to acknowledge the biophysical structure of river landscape where ecosystem services are generated. Therefore, the purpose of this review is to synthesize the literature to develop the understanding of the biocomplexity of river landscapes and its importance in ecosystem service research. The review is limited to anthropogenic modifications from catchment to reach scale which includes inter-basin water transfer, change in land-use pattern, sub-surface modifications, groundwater abstractions, stream channelization, dams, and sand mining. Using 86 studies, the paper demonstrates that river ESs largely depend on the effective functioning of biophysical processes, which are linked with the geomorphological, ecological, and hydrological characteristics of river landscapes. Further, the ESs are linked with the economic, ecological, and socio-cultural aspect. The papers show that almost all anthropogenic modifications have positive impact on economic value of ESs. The ecological and socio-cultural values are negatively impacted by anthropogenic modifications such as dams, inter-basin water transfer, change in land-use pattern, and sand mining. The socio-cultural impact of ground-water abstraction and sub-surface modifications are not found in the literature examined here. Further, the ecological and socio-cultural aspects of ecosystem services from stakeholders’ perspective are discussed. We advocate for linking ecosystem service assessment with landscape signatures considering the socio-ecological interactions.

Background. The East Kolkata Wetlands in India (a Ramsar site) are sewage-fed, nutrient-rich water bodies successfully used for fish production. The vermiculated sailfin catfish, Pterygoplichthys disjunctivus (Weber, 1991), exotic to India, has invaded these wetlands. The management and control of this catfish has been hindered, because of the lack of information on its abundance, population structure, biological traits, level of establishment, and competition with native fish species. Materials and methods. Within 2013–2015 studies were carried out on the population structure of P. disjunctivus, its food habits, reproductive biology, and initial impacts in the wetlands through monthly and seasonal collection of samples, examination of food items, reproductive parameters, catch data, and gathering fishers experience. Results. The length (TL) and weight of the specimens ranged from 10 to 55 cm and from 120 to 1250 g, respectively. Major food items of the catfish were detrital matter (%IRI 56), unidentified plant matter (%IRI 11), fish eggs (%IRI 11), polychaete worms (%IRI 5), and other minor items (%IRI 0.3 to 4). At 50% similarity, the food items of P. disjunctivus overlapped with that of Macrognathus pancalus, Channa punctata, Nandus nandus, Anabas testudineus, Clarias batrachus, Oreochromis niloticus, Cirrhinus mrigala, and Cyprinus carpio while at 80% it overlapped with that of C. mrigala and C. carpio. The fecundity of P. disjunctivus, in the wetlands, was the highest recorded for the species. Females attained the first maturity at 24 cm TL and reproduced multiple times within July–November. The breeding period of the species overlapped with 13 native fish species, of which it seriously overlapped with that of Gudusia chapra, Amblypharyngodon mola, Pethia conchonius, P. ticto, N. nandus, C. punctata, and A. testudineus. The sailfin catfish has established reproducing populations in the wetlands and reached ‘invasive’ proportions constituting 4.83% (300.04 t · year^–1) of the mean annual fish catch (6203.85 t · year^–1) from the wetlands. The invasive risk assessment showed a high risk of the species in the current scenario and probable climate change scenarios in future in the region. Conclusions. Pterygoplichthys disjunctivus has successfully colonized the sensitive East Kolkata Wetlands, which might easily spread to neighbouring water bodies including the sensitive Ganga River and Sundarban mangroves and cause ecological and economic disturbance unless preventive measures are taken as the species has high invasive risk in the region.