Abstract
Seasonally fluctuating water levels, known as ‘flood pulses’, control the productivity of large river fisheries, but the extent and mechanisms through which flood pulses affect fishery yields are poorly understood. To quantify and better understand flood pulse effects on fishery yields, this study applied regression techniques to a hydrological and fishery record (years 1993–2004) for 42 species of the Amazon River floodplains. Models based on indices of fishing effort, high waters and low waters explained most of the interannual variability in yields (R2=0.8). The results indicated that high and low waters in any given year affected fishery yields two and three years later through changes in fish biomass available for harvesting, contributing 18% of the explained variability in yields. Fishing effort appeared to amplify high and low water effects by changing in direct proportion to changes in fish biomass available for harvesting, contributing 62% of the explained variability in yields. Although high waters are generally expected to have greater relative influence on fishery yields than low waters, high and low waters exerted equal forcing on these Amazonian river-floodplain fishery yields. These findings highlight the complex dynamics of river-floodplain fisheries in relation to interannual variability in flood pulses.
Highlights
Fluctuating water levels, known as ‘flood pulses’, control the structure and function of large river ecosystems [1]
Previous studies have shown that flood pulses influence the dynamics of fish populations and 2 associated fishery yields
This study addressed the following questions: (i) do flood pulses influence multispecies fishery yields when fishing effort is accounted for? (ii) Are fishery yield responses to flood pulse variability explained by feeding strategies? (iii) What is the relative strength of the influence of high and low waters on fishery yields? These questions were addressed through analyses of 12 years of data on water levels and fishery yields and effort for 42 species in a river-floodplain of the Amazon Basin that is near-pristine hydrologically
Summary
Fluctuating water levels, known as ‘flood pulses’, control the structure and function of large river ecosystems [1]. Flood pulses promote high rates of biological production and drive the generally high productivity of large river fisheries that provide food and income to millions of people globally [2,3,4]. Previous studies have shown that flood pulses influence the dynamics of fish populations and 2 associated fishery yields. Fish growth and recruitment rates generally increase as fish find protection from predators and abundant plant-based food resources, including algae, detritus, and tree fruits and seeds [7,8]. Declining water levels trigger mortality processes by constraining fish to river channels and floodplain lakes, where increased fish densities intensify predation rates and water quality is often poor [4,9,10,11,12,13,14]. Flood pulse indices in a given year have been correlated with annual multispecies yields or standing biomass in subsequent years: 92% in the Niger, 82% in the Shire, 57% in the Kafue and 83% in the Amazon [4,17]
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