Native Fish Loss in a Transition-Zone Stream Following Century-Long Habitat Alterations and Nonnative Species Introductions

Haworth, Matthew R.; Bestgen, Kevin R.; Kluender, Edward R.; Keeley, William H.; D'Amico, Donald R.; Wright, Felicity

doi:10.3398/064.080.0403

Cited by 1 publication

(3 citation statements)

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“…Flooding may also have dispersed Brown Trout into downstream reaches, particularly smaller individuals (Valdez et al, 2001). However, downstream expansion and increased abundance of Brown Trout in the transition zone of the Poudre River, as well as multiple other nearby streams, were noted prior to the 2013 flood (Haworth et al, 2020;Treble & Battige, 2019).…”

Section: Discussionmentioning

confidence: 99%

“…Flooding may also have dispersed Brown Trout into downstream reaches, particularly smaller individuals (Valdez et al., 2001). However, downstream expansion and increased abundance of Brown Trout in the transition zone of the Poudre River, as well as multiple other nearby streams, were noted prior to the 2013 flood (Haworth et al., 2020; Treble & Battige, 2019). This indicates increased abundance at downstream sites cannot be solely attributed to physical transport and/or habitat changes caused by the flood but was likely aided by it after already becoming established in downstream locations.…”

Section: Discussionmentioning

confidence: 99%

“…Streams in the transition zone typically flow through large urban population centers with high numbers of low‐head dams and are likely to be listed as impaired based on one or more water quality criteria. Low‐head dams in the transition zone are especially problematic for streams draining east of the Continental Divide because those areas historically supported unique fish assemblages with high endemism and peripheral or isolated populations of more widespread taxa (Fausch & Bestgen, 1997; Rahel & Hubert, 1991) and contribute to reduced native fish diversity and abundance (Fausch & Bestgen, 1997; Haworth et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

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Low‐head dam fragmentation, habitat alteration, and invasive predators degrade a Western United States stream fish assemblage

Haworth,

Bestgen

2024

Ecology of Freshwater Fish

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Dams fragment streams, alter hydrology and habitat, and facilitate establishment of nonnative species worldwide to the detriment of native biota. Understanding and mitigating these effects to conserve and restore stream fish assemblages has relied on short‐ and long‐term datasets to assess acute and chronic change through time, craft management strategies, and measure remediation success. We used sampling records collected over a 29‐year period (1993–2021) to examine likely causes of fish assemblage change in the Cache la Poudre River, Colorado, USA. Numerous low‐head dams have reduced connectivity and altered flow, temperature, and habitat in the transition zone, a reach that historically supported rare and sensitive taxa valuable to regional biodiversity. We found diversity, distribution, and abundance of native species declined since the early 1990s, with formerly rare taxa extirpated and some common species becoming rare. Native taxa remained numerically dominant in warmer downstream reaches most affected by streamflow diversion but were incrementally reduced in richness and abundance upstream of low‐head dams without fishways. Concurrently, nonnative Brown Trout Salmo trutta increased in distribution and abundance, dominating upstream reaches that receive cooler and more stable flows, and expanding into downstream reaches where they were formerly absent, with likely negative consequences for native fishes. In the absence of mitigation, these collective effects, plus recent wildfire disturbance and future water development, will continue to degrade stream fish assemblages in our study area, and worldwide, where resource managers face the often‐competing interests of conserving native species, providing recreational fisheries, and meeting increasing water demands.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%