Food habits of Selected Fish Species in the Shenandoah River Basin, Virginia

Food habits of redbreast sunfish (Lepomis auritus), smallmouth bass (Micropterus dolomieu), and white sucker (Catostomus commersoni) populations in the Shenandoah River Basin, Virginia, were assessed during 2002 to identify dietary pathways and patterns potentially affecting mercury uptake. Aquatic insects (71% to 83%) were the principal food item of redbreast sunfish, while smallmouth bass mainly consumed aquatic insects (32% to 48%), crayfish (19% to 31%), and fish (22% to 29%). Principal food items of white sucker included aquatic insects (20% to 26%) and detritus (66% to 70%). Dipterans, ephemeropterans, and trichopterans were the main taxa of aquatic insects consumed by all species. As redbreast sunfish and smallmouth bass increased in size, redbreast sunfish diversified their diet, while smallmouth bass shifted from a diet mainly composed of aquatic insects to one primarily composed of crayfish and fish. Seasonal dietary shifts included decreased consumption of aquatic insects from spring to fall by smallmouth bass and white sucker and increased consumption of terrestrial insects during summer and fall and reduced consumption during winter by redbreast sunfish and smallmouth bass. Smallmouth bass in the South Fork of the Shenandoah River were more dependent on aquatic insects at larger sizes and for longer periods than smallmouth bass in the South River and North River, which consumed greater percentages of crayfish. Differences in forage fish composition were also noted among rivers for smallmouth bass. Results of this study have uncovered important dietary pathways and patterns potentially affecting mercury uptake by the selected fish species and provided the foundation necessary for future investigations concerning mercury dynamics in the aquatic food web of the Shenandoah River Basin and ultimately remediation efforts. Key words: food habits, mercury, redbreast sunfish, smallmouth bass, white sucker

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