Fishing down the food chain revisited: Modeling exploited trophic systems

Several highly cited papers suggest that commercial fishing is altering marine ecosystems by “fishing down the food chain”. Recent evidence calls into question the generality of the original findings, but the papers all raise the question: what mechanisms lie behind exploitation patterns in a trophic system? This paper develops a simple model that shows how economic factors drive patterns of exploitation in a trophic system. We show that while fishing down the food chain is possible, there is no reason to suppose that the relevant economic factors favor such an outcome. As we show, other patterns are just as plausible. We also discuss and show how an index of trophic level-weighted harvest is not necessarily a good indicator of ecosystem health if biomass abundance is important.

► Pauly asserts a “fishing down the food chain” effect of sequential overexploitation. ► We explore how economic factors affect patterns of exploitation in a trophic system. ► We replicate Pauly's hypothesized sequential exploitation of top level predators. ► We also show that fishing up the food chain is as likely as fishing down the chain. ► We contrast indices based on trophic levels of harvests with biomass-based measures.