Effects of Flow Restoration and Exotic Species Removal on Recovery of Native Fish: Lessons from a Dam Decommissioning

Abstract

Flow diversion and invasive species are two major threats to freshwater ecosystems, threats that restoration efforts attempt to redress. Yet, few restoration projects monitor whether removal of these threats improve target characteristics of the ecosystem. Fewer still have an appropriate experimental design from which causal inferences can be drawn as to the relative merits of removing exotic fish, restoring flow, or both. We used a dam decommissioning in Fossil Creek, Arizona, to compare responses of native fish to exotic fish removal and flow restoration, using a beforeafter-control-impact design with three impact treatments: flow restoration alone where exotics had not been present, flow restoration and exotic fish removal, and flow restoration where exotics remain and a control reach that was unaffected by restoration actions. We show that removal of exotic fish dramatically increased native fish abundance.Flow restoration also increased native fish abundance, but the effect was smaller than that from removing exotics. Flow restoration had no effect where exotic fish remained, although it may have had other benefits to the ecosystem. The cost to restore flow ($12 million) was considerably higher than that to eradicate exotics ($1.1 million). The long-term influence of flow restoration could increase, as travertine dams grow and re-shape the creek increasing habitat for native fish. But in the 2-year period considered here, the return on investment for extirpating exotics far exceeded that from flow restoration. Projects aimed to restore native fish by restoring flow should also consider the additional investment required to eradicate exotic fish.

Advancing Environmental Flow Science: Developing Frameworks for Altered Landscapes and Integrating Efforts Across Disciplines

“…This is highlighted by the fact that few studies have weighed the relative contributions of flow regime restoration and nonnative species removal to the conservation of native biodiversity. However, Marks et al (2010) demonstrated that flow restoration had a smaller effect on native fish species abundance in comparison to removal of non-native species, which was achieved for a greatly reduced economic cost. The authors suggest that in areas where non-native species are still established flow restoration had no effect (Marks et al 2010).…”

“…However, Marks et al (2010) demonstrated that flow restoration had a smaller effect on native fish species abundance in comparison to removal of non-native species, which was achieved for a greatly reduced economic cost. The authors suggest that in areas where non-native species are still established flow restoration had no effect (Marks et al 2010). To both minimize the persistence and spread of non-native species, while promoting conservation of native taxa, a structured approach that considers the likely response of all species within the community to flow regime restoration is warranted.…”

“…For example, the spread of Tamarix species in the USA has been linked to the reduction of high-flow events following river regulation, once established Tamarix stands drive sediment aggregation and channel narrowing further altering the hydrological regime and instream habitat (see Tickner et al 2001). Therefore, feedbacks between individual threats may result in potential unintended Environmental Management consequences from restoration, such as restored flow conditions benefiting non-native species (Marks et al 2010). Although examples of flow regime restoration leading to the reestablishment of native species are apparent in the literature (e.g., Scoppettone et al 2005;Kiernan et al 2012), both positive and negative ecological feedbacks have been observed and predicted (Reich et al 2010).…”

Does Feeding Behavior Facilitate Trophic Niche Partitioning in Two Sympatric Sucker Species from the American Southwest?

“…Gut-content studies support this hypothesized diet partitioning: Sonora suckers consume more invertebrate prey than desert suckers, both in terms of gut content volume (58% vs. 14%, respectively) and frequency of occurrence in guts (97% vs. 70%), whereas desert suckers consume more filamentous algae and diatoms than Sonora suckers by both volume (10% vs. 1.5%, respectively) and frequency (72% vs. 40%; Clarkson and Minckley 1988). Stable isotope analyses also indicate a higher proportion of animal tissue in the diet of Sonora suckers relative to desert suckers (Marks et al 2010;Pilger et al 2010), which provides further support for the hypothesis of trophic niche partitioning.…”

Dam removal and anadromous salmonid (Oncorhynchus spp.) conservation in California

“…Bed loads of natural materials will encourage lateral migration of the stream channel, increasing habitat diversity and connectivity to the river floodplain , assuming downstream habitats are not constrained by levees and bank armoring. Restoration of naturally dynamic flows can increase native fish abundance where nonnative fishes are few or removed (Marks et al 2010). Upon dam removal, anadromous salmonids will likely recolonize newly accessible habitats (Anderson and Quinn 2007;Brenkman et al 2008b;Nicole 2012;Engle et al 2013), facilitating the return of locally extripated species.…”