Abstract
The influence of the flood pulse on fish populations has been posited, but infrequently tested or quantified. Here, we tested the effect of habitat on population size, using Prochilodus nigricans as a case study species. Floodplain habitat was based on the littoral zone area occupied by P. nigricans to feed. The magnitude of this habitat in each hydrological year, the moving littoral (ML), was expressed as the sum of daily littoral areas during the advancing flood pulse, using satellite-based passive microwave data. Annual population size was estimated by age class, using a dynamic age-structured model (MULTIFAN-CL) based on catches, effort and fish length frequencies from the Manaus-based fishery over 12.75 years. The principal null hypothesis was that the ML, using three lag times, had no effect on population size of a single age class of P. nigricans. The population size at 29 months of age was positively related (p = 0.00030) to floodplain habitat (ML) earlier in the same year, when the fish were 21–27 months old. The result implies a density-dependent relationship for the population with respect to its feeding habitat. Potential mechanisms governed by flood pulse variation and habitat quality for this and other species using floodplain habitats are discussed.
Highlights
How does a fish population respond to hydrological variation in a river floodplain? This question can be indirectly addressed by analysing a time series of fishery yield as a function of hydrological variables that are thought to increase or decrease
In the central Amazon floodplain, the post-larval and young juvenile fish were found in the moving littoral (ML) from 0 to 3 m depth corresponding to up to about 100 m from the current shoreline
This has been proposed as a factor to compare river-floodplain systems [11], and for explaining fish growth differences within hydrological seasons [30], but it has not been used for year-to-year effects within a system
Summary
How does a fish population respond to hydrological variation in a river floodplain? This question can be indirectly addressed by analysing a time series of fishery yield as a function of hydrological variables that are thought to increase or decrease. The null hypothesis we tested, using various lag times, is that the magnitude of floodplain habitat availability, as influenced by the annual hydrological regime, has no effect on the population size of a given age class of P. nigricans. We used fishery data to estimate annual population size by age class and a combination of field samples and remote-sensing data to derive estimates of the amount of floodplain habitat available to P. nigricans for each hydrological year. Our study is organized as follows: first we describe Prochilodus life history, including habitat use and growth of P. nigricans in the study area (figure 1) This information is combined with hydrological and remote-sensing data to provide annual estimates of the magnitude of the moving littoral (ML) habitat [10,11] preferred by this species when occupying the floodplain. Background and methods are included as appropriate in the following four sections
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