Interannual flow variability in a large subtropical–temperate floodplain: a challenge for fish reproduction

Abstract

Fluctuations of temperature and water levels are the two main drivers of aquatic life in river floodplain ecosystems. The large Middle Paraná River floodplain exhibits marked seasons and important interannual hydrological changes. Using a three-factor-based approach (fish reproductive traits, hydroclimatic conditions, and floodplain recruitment patterns), we analyzed how fish life history evolves within this fluctuating environment. We observed that hydroclimatic conditions can be considered through three main interannual variations that prompt the most abundant Paraná species to adopt four different main reproductive strategies: (i) typical periodic strategists are dependent on large spring–summer floods and juveniles strongly predominate in the floodplain when such a condition occurs, (ii) periodic–opportunistic strategists are associated with floods, regardless of their timing, (iii) periodic–equilibrium strategists take advantage of spring–summer floods whatever the intensity and duration, and (iv) equilibrium strategists have low flood dependence and higher stability in temporal fish recruitment. This work brings forth a first synthesis of fish life history in the Middle Paraná River and evidences how important both hydrological and temperature fluctuations are to interpret its complexity.

Discrimination of hydrologic variations for spatial distribution of fish assemblage in a large subtropical temperate river

“…In HFP, the highest SCBD were found in species with diverse life histories, and they have sedentary behaviors, or make short lateral migrations into the floodplain or long upstream migrations. These characters support the transitional nature of this hydrological phase (see species reproductive traits in Abrial et al, )…”

Variability of hydrological connectivity and fish dynamics in a wide subtropical–temperate floodplain

“…Fish were collected by gill nets of various mesh size (3, 4, 5, 6, 7, 8, 10, 12, 14, and 16 cm between opposite knots), covering an area of 180.9 m 2 and checked every 8 hr while fishing for over 24 hr. Supplementary information on the characteristics of the study area and the methodology of fish sampling is available in Abrial et al () and Espínola et al ().…”

“…Floodplain connectivity was quantified, at different river levels, as the areas of lentic environments connected to the lotic ones within a total area of 15 km 2 containing all sampling sites (Figure b). The methodology based on the processing of satellite images is provided in Abrial et al (). This methodology allows to calculate the exact surface of flooded areas available for fish along the range of water levels occurring during the studied period (eight values from 2.3 to 6.4 m).…”

“…The middle reach of the Paraná River (MPR; Argentina) presents a huge floodplain in a subtropical–temperate low‐land region characterized by five main geomorphic units (Iriondo, Paggi, & Parma, ). In the tributary deltas (the present study takes place in this geomorphic unit), seasons are marked, and floods, which do not necessarily occur in phase with the warm period, strongly modify the accessibility and amount of flooded areas for fish (Abrial, Espínola, Rabuffetti, Amsler, & Wantzen, ). These conditions are likely to trigger significant fish movements from one place to another, as it has been defined in other floodplains (e.g., Fernandez, ; Wantzen et al, ).…”

“…Other factors that may influence fish structures such as water composition and seasonality are also considered. Nonetheless, knowing the strong variations of connectivity within tributary deltas (Abrial et al, ), we expect fish assemblages to respond primarily to this environmental factor, allowing us to identify the river heights that trigger the following ecological changes in the floodplain: fish dispersion into the new flooded areas, fish concentration into the remaining floodplain lakes, and migrations back to the minor channels acting as fish refuges during low waters.…”