Top-Down Control

Top-down control is the regulation of a marine food web by predators, where the abundance of higher trophic levels limits the levels below them. Removing apex predators through fishing can release their prey, which then suppress the next level down, a trophic cascade documented in systems where collapsing cod and shark stocks let mesopredators and forage species surge. It contrasts with bottom-up control, where nutrient supply and primary production set the ceiling. Both operate at once in most systems; ecosystem-based fisheries management weighs top-down effects that single-species assessment, which fixes natural mortality, cannot represent.