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USGS2026

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.

Nebraska↗

USGS2024

Retention of p-Chip microtransponders and posttagging survival of small-bodied stream fishes

Objective Obtaining demographic rates often requires complex open-population capture–mark–recapture (CMR) study designs. Conducting such studies for small-bodied fishes has been limited in part by excessive mortality after tagging procedures and poor tag retention. As new tag types emerge, information regarding fish survival and tag retention over varying time scales may benefit resource managers to effectively plan future CMR studies. The p-Chip microtransponder is a 500- × 500- × 100-μm tag that is inserted subcutaneously and is read with a handheld laser. Each tag contains a nine-digit unique identification number. P-Chip microtransponder tags have been used on a limited number of small-bodied fishes, with relatively high rates observed for fish survival and tag retention. Information on posttagging survival and retention of p-Chip microtransponder tags across a range of small-bodied fish species and tagging locations is needed to inform their effectiveness in future CMR studies. Methods We quantified survival and tag retention after p-Chip microtransponder implantation in Creek Chub Semotilus atromaculatus and Northern Pearl Dace Margariscus nachtriebi in a laboratory environment, and retention of p-Chip microtransponder tags in Northern Pearl Dace was also quantified over a year-long field study. We marked 56 Creek Chub and 9 Northern Pearl Dace in the laboratory with p-Chip microtransponder tags and compared them to an equal number of unmarked individuals over 90 days. We marked 1990 Northern Pearl Dace and conducted recapture events through four seasons (June, September, and October 2022 and June 2023) in four headwater streams of Nebraska. Result Survival for Creek Chub was 85% (standard error [SE] = 5.9) and did not differ from control fish survival (95%; SE = 3.2) in the 90-day laboratory experiment. Survival for Northern Pearl Dace was 89% (SE = 11.0) and did not differ from that of control fish (100%) in the laboratory experiment. Tag retention was 89% (SE = 4.6) for Creek Chub and 100% for Northern Pearl Dace in the laboratory. The p-Chip microtransponder performed well during the CMR field study, with tag retention for Northern Pearl Dace at 94% across 374 days. Conclusion Our results suggest that the p-Chip microtransponder minimally affected small-bodied fish survival and had high tag retention in both the laboratory and field studies. Thus, the p-Chip microtransponder tag may be appropriate for use in small-bodied fishes when individual identification is needed in a CMR study.

North American Journal of Fisheries Management↗