Abstract
Fishes were sampled on the restored floodplain of the Cosumnes River in Central California in order to determine patterns of floodplain use. The floodplain was sampled for seven years (1998-2002, 2004-2005) during the winter-spring flooding season. The fishes fell into five groups: (1) floodplain spawners, (2) river spawners, (3) floodplain foragers, (4) floodplain pond fishes, and (5) inadvertent users. Eight of the 18 abundant species were natives, while the rest were aliens. There was a consistent pattern of floodplain use, modified by timing and extent of flooding. The first fishes to appear were floodplain foragers, inadvertent users, and juvenile Chinook salmon (river spawners). Next were floodplain spawners, principally Sacramento splittail and common carp. At the end of the season, in ponds of residual water, non-native annual fishes, mainly inland silverside and western mosquitofish, became abundant. Adult spawners left when inflow decreased; their juveniles persisted as long as flood pulses kept water levels up and temperatures low. Juvenile splittail and carp quickly grew large enough to dominate floodplain fish samples, along with smaller numbers of juvenile Sacramento sucker and pikeminnow (river spawners). Such juveniles left the Relatively few fishes that used the floodplain for spawning or rearing became stranded, except late season alien fishes. Most alien fishes had resident populations in adjacent river, sloughs, and ditches and were not dependent on the floodplain for persistence. This indicates that Central Valley floodplains managed to favor native fishes should have the following char- acteristics: (1) extensive early season flooding, (2) complete drainage by the end of the flooding season, (3) few areas with permanent water, (4) a mosaic of physical habitats, (5) regular annual flooding but with high variability in flood regime.
Highlights
California, like most other regions of the western world, has placed levees between its rivers and their floodplains, to free land for farms and cities
Fishes use floodplains in many different ways, the widely used classification system developed for European rivers divides them into just three categories: (1) species with a strong dependence on the river, (2) species that live mainly in backwaters and floodplain lakes, and (3) species that occur in both broad habitat types (e.g., Grift et al 2003)
The 16 species captured on a regular basis were about divided among rheophilic, eurytopic, and limnophilic species, rheophilic species dominated at the beginning of flooding season and limnophilic species dominated at the end (Figure 5)
Summary
California, like most other regions of the western world, has placed levees between its rivers and their floodplains, to free land for farms and cities. Eurytopic fishes are labeled “grey fishes.” Galat and Zweimuller (2001) assessed the importance of floodplain habitats by dividing fish into three categories: fluvial specialist species, fluvial dependent species, and microhabitat generalists. Their fluvial specialists are basically rheophilic species that are found only in flowing water, while the fluvial dependent species are a subset of rheophilic and limnophilic species that require rivers for some stage of their life history. Their microhabitat generalists include eurytopic species plus less specialized limnophilic species
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