Fish movement, habitat selection, and stream habitat complexity in small urban streams

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2006-08-04

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Urbanization impacts have become more evident in the last 30-50 years, due to human population increase and subsequent land use change. Many aspects of stream ecosystems are influenced including hydrology, geomorphology, water quality, ecosystem function, riparian vegetation, and stream biota. Effects of urbanization on ecosystem structure and function are discussed, and the urban stream syndrome is introduced in Chapter 1. Chapter 2 reports differences in stream fish assemblages in the eastern Piedmont and Coastal Plain of Maryland, USA due to urbanization, and establishes a foundation for hypotheses presented in subsequent chapters. Chapter 3 describes a physical habitat survey that attempts to understand what instream and channel habitat attributes change across the urban-rural gradient (0-81% urban land use; ULU). While changes in stream habitat appear at 30% ULU, significant impacts occurred once a watershed has >45% ULU, at which point stream channels can not accommodate the power and intensity of impervious surface runoff. Fish habitat patch selection is examined in Chapter 4, which involved instream habitat manipulation experiments. I tested fish selection response of instream habitat using three treatments (woody debris, shade, and both) in first order urban (>60% ULU), suburban (27-46% ULU), and rural (<15% ULU) eastern Piedmont streams in Maryland. Blacknose dace (BND) Rhinichthys atratulus and creek chub (CKB) Semotilus atromaculatus selected shade and woody debris combined significantly more than other treatments in rural and suburban streams. Urban fish selected the shade treatment the most of all enhancements. CKB who selected the enhancement were significantly larger than those found in the control. Urban fish prefer shaded habitat providing overhead protection due to the general lack of habitat complexity in urban channels. CKB behavior may indicate intraspecific competition, particularly between juvenile and adult individuals for prime habitat positions. Chapter 5 presents a fish movement study, comparing rural and urban fish population behaviors. Urban BND and CKB displayed significantly larger home ranges than rural fish. The rural fish movement distribution was more leptokurtic. Competitive interactions are suggested as the reason for greater movement in urban stream populations. Finally, conclusions are submitted with significant findings in Chapter 6.

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