Spatial variation in invasive silver carp population ecology throughout the upper Mississippi River basin*

Abstract

Understanding spatial variation in non-native fish species population ecology is imperative, where environmental, biotic and invasion-related mechanisms contribute to spatial heterogeneity. Established populations of invasive silver carp Hypophthalmichthys molitrix are currently found throughout a large portion of the upper Mississippi River (UMR) basin. Despite their recent invasion and broad environmental tolerances, silver carp population ecology and linkages to environmental conditions in the UMR remain understudied. There were two objectives for this investigation: (a) to estimate correlations among population characteristics and the influence of latitude and the time since first detection, and (b) to model the influence of river discharge and temperature on growth early in life to age 3. We estimated spatial variability in silver carp population characteristics and dynamics from nine sites across the UMR and assessed if biotic, abiotic or invasion-related (time since first detection) variables influence spatial patterns. Silver carp body weight, size structure, annual mortality, and growth parameters varied among locations. Silver carp recruitment was less stable for populations with higher relative abundance estimates and where carp were first detected ≥20 years ago whereas maximum carp age decreased with increasing latitude. Although model selection indicated silver carp length at age 3 was associated with mean daily discharge (m3/s) coefficient of variation, mean May-June temperatures, and ordinal date of maximum discharge, parameter coefficients and effect sizes were small and not biologically meaningful. Our results suggest that silver carp populations are governed by intraspecific mechanisms, but time-dependent changes in populations may partially underpin heterogeneity across populations. Our study helped further disentangle silver carp population ecology in the UMR by understanding carp ecology as a function of their invasion.

Evaluating the spatial and temporal distribution and ecology of Bighead and Silver Carp and native fishes of the lower Red River basin

“…Additionally, TL for newly established populations of Silver Carp in the Mississippi River and Bighead Carp in the Missouri River ranged from 600 to 800 mm and 450 to 1,099 mm, respectively(Schrank and Guy 2002;Williamson and Garvey 2005).It is unknown where Carp recruit in the Red River catchment. Silver Carp recruitment variability was relatively stable (RVI of 0.86), which is comparable to what is observed in other catchments such as the Missouri, Mississippi, De Moines, and Wabash rivers (RVI 0.66 -0.95,Sullivan et al 2021). This may be due to fish consistently recruiting to the catchment from other river systems (i.e., (k = 0.31) was similar to that of populations in the Mississippi and Illinois rivers (0.23 -0.445,Tsehaye et al 2013, Sullivan et.…”

“…Silver Carp recruitment variability was relatively stable (RVI of 0.86), which is comparable to what is observed in other catchments such as the Missouri, Mississippi, De Moines, and Wabash rivers (RVI 0.66 -0.95,Sullivan et al 2021). This may be due to fish consistently recruiting to the catchment from other river systems (i.e., (k = 0.31) was similar to that of populations in the Mississippi and Illinois rivers (0.23 -0.445,Tsehaye et al 2013, Sullivan et. al 2021, whereas Bighead Carp growth rate (k = 0.12) was slower relative to Mississippi River populations (0.433,Tsehaye et al 2013).…”

“…Furthermore, rivers with robust populations of Silver Carp have relatively smaller fish. For example,Sullivan et al (2021) found that the mean TL for Silver Carp ranged from 532 -737 mm in the Missouri, Mississippi, Wabash, and Illinois rivers, whereas the mean TL was 887 mm in our samples from the lower Red River catchment. Atchafalaya River) or steady recruitment in the Red River.…”

Estimating fish mortality rates from catch curves: A plea for the abandonment of Ricker (1975)'s linear regression method

“…Given the different analytical shortcomings of the LR method, the CR and CRCB methods have sometimes been preferred to estimate mortality rates (e.g., Clark et al, 2023;Coulson & Poad, 2021) if not the WLR method instead (e.g., Jefferson et al, 2021;Sullivan et al, 2020).…”

“…Given the different analytical shortcomings of the LR method, the CR and CRCB methods have sometimes been preferred to estimate mortality rates (e.g., Clark et al ., 2023; Coulson & Poad, 2021) if not the WLR method instead (e.g., Jefferson et al ., 2021; Sullivan et al ., 2020). Although the CRCB method constitutes an improvement over its original version (Smith et al ., 2012), it nonetheless requires that Z and its SE must be approximated from S as obtained from the original method to then apply correction factors (Hoenig et al ., 1983; Smith et al ., 2012).…”