A 40+ year programme to monitor brown trout, Salmo trutta L. (populations at 25 groundwater‐fed stream sites in southeast Minnesota, USA, was initiated to identify population trends, evaluate management actions and test ecological theories regulating populations. Significant increases between 1970 and 2018 were found for total biomass (an average of 5% annually) and abundance of juveniles (7%), all adults (7%) and adults ≥305 mm (3%). Sites managed with instream habitat projects had an additional 30% higher abundance for trout ≥305 mm and 57% higher for trout ≥355 mm. Sites managed with a catch‐and‐release regulation had nearly 130% higher abundance of trout ≥305 mm and 100% higher for trout ≥355 mm. Trout recruitment was temporally synchronous over the 9,200 km2 area but not associated with spatial distance. There was little support for stock–recruitment relationships, and density‐dependent growth was only detected at half of the study sites. Increasing abundance trends represent a fisheries management success and suggest that these populations were largely regulated by a coupling of abiotic factors managed at two spatial scales: watershed (improved land use practices facilitating greater water infiltration) and instream (habitat improvement projects).
Species-specific microsatellite DNA markers were used to identify hybrids of black crappies Pomoxis nigromaculatus and white crappies P. annularis and to determine the effect of hybridization on crappie growth. Specifically, we determined the contribution of hybrids to the skew in length frequency distributions that is frequently observed within year-classes of sympatric crappie populations and the resulting upward bias on growth estimates for the two species. Hybridization was found throughout most southern Minnesota lakes that contained both species, but the frequency of hybrids was low in our length-stratified subsamples (mean frequency of first-generation [F 1 ] hybrids among all lakes and year-classes ¼ 3.2%; mean frequency of advanced-generation [F x ] hybrids ¼ 1.4%). Among the 22 study lakes, only 2 contained no hybrids (based on polymerase chain reaction amplification of microsatellite loci). The F 1 hybrids were disproportionately classified as black crappies under a Minnesota Department of Natural Resources (MNDNR) classification system that only allowed assignment of crappies to the two parental species. In one lake sampled over multiple years, we found F 1 hybrids in only 5 of 14 year-classes of MNDNR-classified black crappies and in 4 of 11 year-classes of MNDNR-classified white crappies, indicating annual variation in the prevalence of hybridization. Consistent with their faster growth and tendency to be classified as black crappies, F 1 hybrids accounted for 82% of all statistical outliers in length distributions of MNDNR-classified black crappie age-classes and 33% of the infrequent outliers in MNDNR-classified white crappie age-classes. The presence of F 1 hybrids in our subsamples produced an upward bias in back-calculated length estimates for black crappies but had nonsignificant effects on white crappie length estimates. The effects of hybridization should be taken into account when estimating growth in crappie species from sympatric populations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.