Flood pulse effects on multispecies catch in the Amazon Basin

Abstract

Tropical river-floodplain fisheries feed tens of millions of people and depend on the flood pulse, the seasonal rise and fall of water that drives fish recruitment, growth, and catch. Yet we cannot predict how catch will respond to changing flood regimes. Evidence is fragmented; most models emphasize high-water dynamics while ignoring low-water dynamics, and species-specific responses are rarely linked to the life-history traits that shape them. These gaps matter, as dams, deforestation, and climate change reshape flood pulses worldwide. This dissertation builds a mechanistic, trait-based, and climate-forward understanding of the flood pulse–fish catch relationship in the Brazilian Amazon. I synthesized evidence from 27 studies across tropical basins. I then paired 20 years of daily fish landings (1991–2011) from 11 Amazon ports with daily water levels to identify which flood pulse features drive catch, tested whether life-history traits moderate taxon-level responses across 14 dominant taxa, and projected catch to 2100 under climate scenarios. A composite hydrological signature capturing prolonged high water, elevated minimums, and gradual rises, lagged two years, predicted catch better than any single metric, explaining 78% of the deviance. Size at maturity most strongly moderates species responses: early-maturing taxa lose up to 22% of catch under high flood conditions, while later-maturing taxa gain up to 11%. Under mid-century climate projections, basin-wide catch appears nearly stable, but this aggregate conceals near-universal declines across 8 of 9 regions and all 14 taxa, concentrated in the drying tributaries. The flood pulse–fish catch relationship is mechanistic, trait-filtered, and forecastable, but basin-wide metrics mask the regional and taxonomic losses where climate impacts are felt. Anticipating impacts in river-floodplain fisheries requires standard hydrological metrics, tributary-scale projections, trait-specific models, and management strategies that match each species' flood sensitivity.