Modelling the food web for assessment of the impact of stock supplementation in a reservoir ecosystem in India

Abstract

Comparative estimates of trophic status and energy flow were carried out in a tropical reservoir ecosystem in India to assess the impact of fish stocking. Mass‐balanced models of the reservoir ecosystem were constructed for two periods – 1982–1983 and 2002–2003 – using ecopath software to determine the impacts on different groups before and after stocking. Mixed trophic impact (MTI) analyses indicated that phytoplankton and detritus have a positive impact on most groups. There was a decrease in nutrient flow through the system from pre‐stocking to post‐stocking (22.28%). The baseline was higher by 0.29% in the post‐stock phase indicating maturity. The ecosystem indices tested indicate that the reservoir was in a more resilient state post‐stocking than during the pre‐stocking phase. The ‘health’ of the ecosystem showed an improvement, which indicates a positive impact of stocking.

Species Distribution Modeling And Assessment of Environmental Drivers Responsible To Distribution And Preferred Niche of Critically Endangered Endemic Ornamental Freshwater Fish Species of The Genus Sahyadria

“…The spatial predicted distribution model was developed for the two important sh species S. denisonii and S. chalakkudiensi in the Western ghat ecosystem and priority ecological niche forecasted relating the relative contribution of bioclimatic features. Though in inland waters few models were reported in sheries (Panikker and Khan, 2008;Khan, 2015;Sarkar, 2019 and2021), however, this is the rst attempt which predicted the geographical distribution of an important species in relation of environmental and climatological dataset. The pattern of distribution range under seasonality was noticed and depicted.…”

Changing foodwebs of Indian aquatic ecosystems under the threats of invasive species: An overview

“…Exotic carps, Cyprinus carpio and Grass Carp, Ctenopharyngodon idella were reported to have a negative impact on murrels and minor carps in Hemavathy reservoir in Karnataka (Khan et al, 2015). Oreochromis mossambicus in Vellayani Lake modeled by Bijukumar et al (2015) was found to have a strong adverse impact on barbs and carpels, and a slight impact on the other native fishes like the needle fishes, gobiids, and nandids.…”

“…In this particular reservoir, nonnative carps Cyprinus carpio and the grass carp, Ctenopharyngodon idella were stocked along with the Indian major carps (Catla catla, Labeo rohita and Cirrhinus mrigala). The biomass of the nonnative carp group was estimated as 0.447 and 2.56 t km -1 year -1 in the fishery during 1982-83 (pre-stock phase) and 2002-03 (post-stock phase) respectively (Khan et al, 2015). The mixed trophic impact routine showed that an increase in biomass of the non-native carps showed a slight negative impact on the eels but did not impact any other fish groups in the ecosystem.…”

“…The introduction of fish in a system through stock supplementation can cause substantial effects on the foodweb (Mbabazi et al, 2004). A mass-balanced model study in Hemavathy, a large reservoir in Karnataka, southern state of India was conducted for two periods (before and after the introduction of fish seeds) using ECOPATH to assess the impact of non-native fish seed stocking on the foodweb of the ecosystem (Khan et al, 2015). In this particular reservoir, nonnative carps Cyprinus carpio and the grass carp, Ctenopharyngodon idella were stocked along with the Indian major carps (Catla catla, Labeo rohita and Cirrhinus mrigala).…”

“…In the Hemavathy reservoir of Karnataka, India (Khan et al, 2015), the trophic flows basically happened in the first four trophic levels and the food -web was characterized by the predominance of low trophic level organisms during the two different phases which were modelled. The comparative trophic models showed a variation in the foodweb structure and system summary statistics in the reservoir during the two phases despite the changes in biomass of the natives and non-native fishes (Khan et al 2015). Connectance index (CI) and omnivory index (OI) are ecological indicators that are correlated with the maturity of the reservoir ecosystem as described by Odum (1971).…”