Flooded flatheads: evidence of increased growth in Mississippi River Pylodictis olivaris (Pisces: Ictaluridae) following the Great Midwest Flood of 1993

摘要

Both the Mississippi and Missouri rivers experienced major flooding in the spring and summer of 1993, inundating much of their floodplains for long periods, and allowing fish access to vast but previously inaccessible benthic foraging areas. In response to the latter, we hypothesized that flathead catfish (Pylodictis olivaris) would exhibit altered post-flooding growth as compared to like-aged fish whose lives were flood-free. To test this hypothesis, we obtained the left pectoral fin spines from hoop-netted Mississippi River flathead catfish collected in the vicinity of Crystal City, Missouri, USA, and conducted an individual-based back-calculated growth comparison of individuals captured pre-flood (1991) and post-flood (1996). For like-aged cohorts, our back-calculated length-at-age data clearly show that the post-flooding growth in 1996-collected fish was superior to that of the 1991-collected fish that had experienced less exceptional flow regimes. This outcome suggests that increased forage or/and foraging opportunities can be a consequence of flooding, and that flathead catfish are able to capitalize on this. The natural flooding regime of big rivers may thus be an important contributor to the growth and success of certain fish species; consequently, modifying the river's natural hydrograph and channel morphology may be detrimental.