Trophic Downgrading

Trophic downgrading describes the reduction in mean ecosystem trophic level caused by the preferential exploitation of large apex predators and the "fishing down food webs" that follows. As top predators are depleted, fishing effort shifts to progressively smaller, lower-trophic-level species. This reduces mean trophic level of the catch and destabilises ecosystem structure through a cascade of trophic interactions. Trophic downgrading has been documented in marine systems globally and is associated with increased primary productivity, harmful algal blooms, and jellyfish outbreaks.

The mean trophic level of global fishery landings declined from ~3.3 in 1950 to ~3.05 by 2010 (Pauly et al. 1998, updated), reflecting the systematic depletion of larger, higher-trophic species and replacement by smaller "forage" fish.