PRESENTATION
B.T. Halloran, B. T., M.D. Kaller, W.E. Kelso, and D.A. Rutherford mahihmahi1@hotmail.com
School of Renewable Natural Resources, Louisiana State University, Baton Rouge, Louisiana, 70803
Abstract
It is believed that fishes in riverine systems have evolved to exploit the seasonal advance of floodwaters. Though the proximate effects of overbank flooding include: (1) the resetting of nutrient cycles; (2) stimulation of primary production; (3) robust zooplankton communities; and, (4) increased hydrological connectivity; it is unclear if the arrival of a floodpulse results in successful fish recruitment. Although, the cue for floodplain‐dependent fish reproduction is thought to originate from a rising springtime hydrograph; post‐flood conditions are often highly unstable and, as a result, potentially lethal for newly hatched fishes with limited motility and strict physiological thresholds.
In the Atchafalaya River basin (ARB), LA., a sub‐optimal physicochemical backcloth (i.e., widespread chronic hypoxia) often overlaps with the peak spawning times of many fishes. Yet, the adult fish community in the ARB is consistently strong, indicating that young‐of‐the‐year survivorship is high. To examine the structuring affects of floodwaters on recruitment, we examined the yearly distribution of larval fishes in limnetic (open water) and floodplain environments. Regardless of flooding regime, we were unable to document abundant and speciose ichthyoplankton communities in recently flooded backwater microhabitats. Our observations found that the most dominant taxa have protracted spawning cycles with larvae that appear to be able to withstand a wide degree of variation in water quality regardless of the scale of inundation. Consequently, reproductive “hedging” for the proper combination of physicochemical and/or flow “windows” might be a disadvantageous approach in hydrologically unpredictable ecosystems, such as the ARB. |