Impact of species enrichment and fishing mortality in three species food chain models

In the present article, we consider two food chain models with three trophic levels: one is 'prey-predator-top predator' system where the top-predator consumes only the predator trophic level and the another one is 'prey-predator-generalist predator' system where the generalist-predator (top trophic level) consumes both the predator and the prey species. We examine the impacts of different levels of nutrient supply to the bottom species (prey) in both the models. We derive conditions when additional nutrient supply cannot bring the top trophic level to coexist in both the systems if the top trophic level is absent prior to nutrient supply. Once the three trophic levels are present prior to an additional nutrient supply, biomass of the predator trophic level reduces or even the predator trophic level goes to extinction in the 'prey-predator-generalist predator' system due to a massive amount of nutrient supply. We also explore the impacts of fishing mortality to achieve maximum sustainable yield (MSY) from individual trophic level. The most important conclusion is that harvesting the predator at MSY level is a sustainable fishing policy in 'prey-predator-generalist predator' system.