Habitat Preferences of the Rainbow Darter, Etheostoma Caeruleum, with Regard to Microhabitat Velocity Shelters

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Microhabitat velocity shelters or flow refugia within the stream bed are important habitat components for benthic fishes such as the rainbow darter (Etheostoma caeruleum), yet actual water velocities within potential flow refugia have not previously been quantified. Rainbow darter water velocity microhabitat preferences in the Mad River, Ohio, were quantified on scales of millimeters using a thermistor flow meter. Water velocities at and directly above (midwater column) observed darter sites were compared to adjacent (within 5 cm) benthic and middepth (0.6) water column velocities to describe the darters' physical microhabitat in terms of dynamic parameters (water velocities). Population assessments in six representative transects were made in conjunction with velocity measurements to determine the role that benthic water velocity plays in rainbow darter habitat selection. The Mad River is a relatively low gradient river with seasonal periods of low discharge (June-Sept.). Darter site velocities were significantly lower than adjacent (< 5 cm) benthic velocities in all months (May-Sept.) and lower than potential habitat benthic velocities in July, August, and September; thus darters were consistently found in microhabitat velocity shelters. Rainbow darter middepth velocities were significantly lower than nondarter-related middepth velocities in May, July, and September, indicating that darters use water column areas, as well as microhabitats, with lower velocities. Rainbow darter microhabitat velocity shelters have average threshold water velocities ≤3-5 cm s-1 across macrohabitat units and seasons. As ambient velocities along the substrate surface increase, physical shelters created by static and dynamic habitat components are the preferred microhabitat choice for this species.




American Society of Ichthyologists and Herpetologists (ASIH)



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