The Effects of Embeddedness on the Seasonal Feeding of Mottled Sculpin

Excess sediment in streams (measured as embeddedness), whether from natural or anthropogenic sources, has adverse effects on the biota that inhabit these systems. Aquatic macroinvertebrates exhibit reductions in diversity and abundance, which in turn leads to a reduction in the availability and quality of food for their fish predators; however, macroinvertebrate communities were not significantly different from one another. The predator-prey relationship between mottled sculpin (Cottus bairdii) and macroinvertebrates was examined in four headwater streams with differing embeddedness levels (15% and 35%) in Garrett County, MD. Embeddedness was not different enough to cause a shift in the macroinvertebrate community. Sculpin in both streams showed a pattern in which larger individuals were consuming larger prey items, and in turn more energy, in certain seasons. This pattern was evident in the summer, autumn, and winter for the 15% embedded streams and spring and autumn for the 35% embedded streams. Compositional analysis revealed that sculpin from the lower embeddedness level were consuming ephemeropterans regardless of their abundance, and sculpin from the higher sediment level preferred chironomids. A reduction in body condition was found at one of the 35% embedded sites, possibly due to consuming smaller, lower energy prey. It may be possible that increasing embeddedness levels are not changing the macroinvertebrate community but might restrict benthic fish access to valuable prey resources.