The Atchafalaya River Basin in south-central Louisiana (USA) comprises the largest contiguous riverfloodplain swamp in North America and functions as a distributary for the Mississippi River to the Gulf of Mexico. We assessed the impact of the annual flood pulse on fisheries production at a basin-wide scale. We modelled flood duration (days/year Butte LaRose gauge height >3.6m) and magnitude (mean daily gauge height) against long term (19872009) fishery-independent and fishery-dependent data on largemouth bass (Micropterus salmoides), crappie (Pomoxis spp.), blue catfish (Ictalurus furcatus), buffalofish (Ictiobus spp.), gizzard shad (Dorosoma cepedianum) and crayfish (Procambarus spp.). When the Atchafalaya River at Butte LaRose is at flood stage ( 3.6m gauge height) for approximately 121157days/year, then annual relative abundances of largemouth bass, crappie, blue catfish and buffalofish are optimized during the fall (OctoberDecember). In contrast to the tenets of the flood pulse concept, gizzard shad abundance was optimized during low flow years, when flood duration is 10days/year. Annual proportion of age-1 largemouth bass was associated positively with flow magnitude during the previous year, whereas proportions of age-2 largemouth bass and crappie were associated positively with flood magnitude 2years prior to the fish sample. Results for commercial production metrics were ambiguous. Crayfish catches were associated positively with flood magnitude and duration, whereas gizzard shad landings peaked at a relatively small flood magnitude level and were not related to flood duration. Blue catfish and buffalofish annual landings were not influenced by the annual flood pulse. The annual flood pulse can be managed to optimize the availability of recreational (largemouth bass and crappie) and some commercial fisheries resources (blue catfish and crayfish). We estimate that a minimum discharge of 8807m3s1 is required at the river's source for approximately 45months during the winterspring months to optimize fisheries production. Copyright (c) 2011 John Wiley & Sons, Ltd.
