Connectivity and flow regime direct conservation priorities for pelagophil fishes

Abstract

1. Dam construction threatens global aquatic biodiversity by fragmenting stream networks and altering flow regimes. The negative effects of dams are exacerbated by increased drought periods and associated water withdrawals, especially in semi-arid regions. Stream fishes are particularly threatened owing to their mobile nature and requirement for multiple habitats to complete their life cycles. An understanding of relationships with fragmentation and flow regimes, particularly as coarse-scale (e.g. catchment) constraints on species distributions, is essential for stream fish conservation strategies. Prairie chub (Macrhybopsis australis) is a small-bodied minnow (Cyprinidae) with poorly understood ecology endemic to the North American Great Plains.Suspected declines in abundance and extirpations have resulted in conservation interest for prairie chub at state and federal levels. Prairie chub is thought to share its reproductive strategy with pelagic-broadcast spawning minnows (pelagophils). Freshwater pelagic-broadcast spawning fishes have been disproportionately affected by fragmentation and streamflow alteration globally.3. Relationships of prairie chub occurrence with coarse-scale fragmentation and streamflow metrics were examined in the upper Red River catchment. Occurrence probability was modelled using existing survey data, while accounting for variable detection. The modelled relationships were used to project the distribution of prairie chub in both a wet and dry climatic period.4. The probability of prairie chub occurrence was essentially zero at sites with higher densities of upstream dams, but increased sharply with increases in flow magnitude, downstream open mainstem, and flood duration. The projected distribution of prairie chub was broader than indicated by naïve occurrence, but similar in both climatic periods. The occurrence relationships are consistent with the hypotheses of pelagic broadcast spawning and represent coarse-scale constraints that are useful for identifying areas of the stream network with higher potential for finer-scale prairie chub conservation and recovery efforts. In addition to informing pelagophil conservation, the relationships are also applicable to pelagic-broadcast spawning fishes in marine environments.

Effects of flow recession regime on stranding of Rio Grande silvery minnow suggests that conservation actions must overcome evolutionary traps

“…However, to make progress towards recovery and self‐sustaining populations, research should focus on how species persisted historically, and design conservation actions that restore or improve those mechanisms (Arthington & Balcombe, 2011; Hoagstrom & Turner, 2015). Among North American freshwater pelagic broadcast spawning minnows, those priorities should be directed towards restoring flow regimes and connectivity among habitats (Mollenhauer et al, 2021). In the absence of actions that restore resistance and resilience mechanisms, species are likely to become or remain conservation‐reliant on resource‐intense actions (Goble et al, 2012), such as augmentation with hatchery fish.…”

Low‐head dam removal increases functional diversity of stream fish assemblages

“…Brood hiders, benthic spawners and pelagophils experienced the greatest increases following removal. This is unsurprising as dams inhibit the flow and connectivity essential to pelagophil reproduction (Durham & Wilde, 2009; Mollenhauer et al, 2021). Dams also alter riverine habitat to become more lacustrine, resulting in sediment build up, aquatic plant growth, finer substrates, and elimination of spawning substrate needed for benthic fish reproduction (Ward & Stanford, 1983; Johnson, Richardson, & Naimo, 1995; Kemp et al, 2011; Keller, Barren, & Horwitz, 2021).…”

A Hierarchical Approach to Fish Conservation in Semiarid Landscapes: A Need to Understand Multiscale Environmental Relationships

“…Thus, both minimal fragmentation and higher flow magnitude are essential to successful recruitment [53][54][55]. There are similarities between pelagophils and marine pelagicbroadcast spawners in juvenile dispersal strategies to microhabitats with high nutrient concentrations and reduced predation pressure [51,56]. High-flow events increase nutrient loads and create disconnected temporary slackwater habitats that serve as nurseries for juvenile pelagophils.…”

“…We used the upstream network density of major dams (UNDR, #/100 rkm) at the outlet of each HRU obtained from an online database [85] to characterize fragmentation. We used UNDR because it was highly correlated with numerous other fragmentation metrics and upstream dams have been shown to be strongly associated with pelagophil distributions in the upper Red River basin [56]. We natural log transformed UNDR prior to modeling due to a right-skewed distribution.…”

“…The findings for our study period are likely reflective of multiscale prairie chub ecological relationships in both wet and dry periods. Occurrence probability among HRUs has been shown to be similar in both wet and dry periods [56], and reach-scale adult counts were collected during a relatively wet period [97].…”