Population dynamics of Northern Pearl Dace Margariscus nachtriebi in anthropogenically altered headwater streams of the Nebraska Sandhills Ecoregion

Empirical evidence of population demographic responses to environmental perturbations is a major knowledge gap for aquatic vertebrate populations. Extensive habitat alteration including channelization of headwater streams influences the habitat template on which small-bodied fish are dependent to carry out distinct life stages and maintain or increase population growth. The objectives of this study were to (1) determine differences in geomorphic characteristics, and instream habitat (i.e., mesohabitat availability, water depth, and macrophyte coverage) in channelized and unchannelized stream sites, and (2) estimate survival of Northern Pearl Dace Margariscus nachtriebi in channelized and unchannelized stream sites. A capture-mark-recapture robust design study was conducted where a total of 1994 Northern Pearl Dace were double tagged and 853 were recaptured over the 374-day field study. Geomorphic characteristics and instream habitat in channelized and unchannelized stream sites differed (Pillai's Trace = 0.950, F(8, 6) = 14.228, p = 0.002). Specifically, mean sinuosity index (F(1, 13) = 20.723, p = 0.0005) and the percentage of pool mesohabitat (F(1, 13) = 4.929, p = 0.045) were both reduced in channelized versus unchannelized stream sites. Northern Pearl Dace seasonal survival was lower in channelized sites (Ŝ_{Spring to Summer} = 0.34; SE = 0.06) compared to unchannelized sites (Ŝ_{Spring to Summer} = 0.93; SE = 0.03) during spring to summer. Annual survival differed between channelized sites (Ŝ = 0.001; SE = 0.009) and unchannelized sites (Ŝ = 0.047; SE = 0.024). Channelization in headwater streams influenced population demographic parameters of stream fish. Northern Pearl Dace exhibited reduced survival in channelized sections of headwater streams flowing through the largest intact grassland ecosystem in North America. Mitigating channelization in streams may benefit persistence of native prairie fishes by increasing survival and subsequently aid in the restoration of headwater streams that flow through grassland ecosystems in North America.