Effects of Road Crossings on Habitat Connectivity for Stream‐Resident Fish

Abstract

Road crossings can act as barriers to the movement of stream fishes, resulting in habitat fragmentation, reduced population resilience to environmental disturbance and higher risks of extinction. Strategic barrier removal has the potential to improve connectivity in stream networks, but managers lack a consistent framework for determining which projects will most benefit target species. The objective of this study is to develop a method for identifying and prioritizing action on road crossings in order to restore stream network connectivity. We demonstrate the method using a case study from the Pine‐Popple watershed in Wisconsin. First, we propose a new metric for quantifying stream connectivity status for stream‐resident fish. The metric quantifies the individual and cumulative effects of barriers on reach and watershed level connectivity, while accounting for natural barriers, distance‐based dispersal limitations and variation in habitat type and quality. We conducted a comprehensive field survey of road crossings in the watershed to identify barriers and estimate replacement costs. Of the 190 surveyed road crossings, 74% were determined to be barriers to the movement of at least one species or life stage of fish, primarily due to high water velocity, low water depth or outlet drops. The results of the barrier removal prioritization show that initial projects targeted for mitigation create much greater improvements in connectivity per unit cost than later projects. Benefit–cost curves from this type of analysis can be used to evaluate potential projects within and among watersheds and minimize overall expenditures for specified restoration targets. Copyright © 2014 John Wiley & Sons, Ltd.

Forestry Best Management Practices Relationships with Aquatic and Riparian Fauna: A Review

“…Maintaining stream channel morphology helps maintain ecological communities and populations of riparian species [72]. To safeguard aerial, terrestrial, and aquatic riparian wildlife, stream crossing designs need to consider river morphology, depth, velocity, stream flow, and scouring potential [80][81][82][83]. These considerations are vital to maintaining healthy wildlife populations; poorly designed stream crossings increase sedimentation, cause issues with aquatic organism passage, influence population dynamics, and contribute to loss of suitable habitat [72,76].…”

“…Legacy stream crossings installed prior to the era of BMPs may require replacement or remediation [57]. Although bridges, which usually can be installed to preserve natural channel shape, are a preferred stream crossing type, particularly over larger streams, other factors such as traffic requirements, structural loading capabilities, site features, and economic feasibility often favor use of other stream crossing types [48,83,84].…”

“…Culverts that are improperly sized for the watershed can have reduced capacity to pass water and sediment or accommodate fish passage [83]. Water velocity at the exit from culverts that are undersized for the watershed can exceed the capacity of the channel and cause greater downstream scour [85].…”

“…Water velocity at the exit from culverts that are undersized for the watershed can exceed the capacity of the channel and cause greater downstream scour [85]. Increased velocity and potential culvert suspension could result in habitat and population fragmentation of aquatic species by creating a barrier to aquatic organism movement upstream [73,76,83,86]. Proper culvert size selection is a very basic BMP application [48].…”

“…With careful planning and knowledge of local options, selection of stream crossing types that allow adequate organism passage can be both cost-effective and ecologically compatible. Some designs, such as open-bottom culverts, can mimic natural channel shape and substrate and preserve natural hydrological attributes [76][77][78]83]. Although research on the effects of stream crossings on riparian and aquatic wildlife other than fish [86,87] are relatively limited [71,77,78], culvert BMPs and culvert design have been shown to influence mussels [88], crayfish [77,78], snails [89][90][91][92], and aquatic insects [93][94][95][96].…”