Hydrology controls recruitment of two invasive cyprinids: bigheaded carp reproduction in a navigable large river

Abstract

In the Mississippi River Basin of North America, invasive bigheaded carp (silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis, also referred to as Asian carp) have spread rapidly over the past several decades. In the Illinois River, an important tributary of the Upper Mississippi River, reproduction appears to be sporadic and frequently unsuccessful, yet bigheaded carp densities in this river are among the highest recorded on the continent. Understanding the causative factors behind erratic recruitment in this commercially-harvested invasive species is important for both limiting their spread and managing their harvest. We analyzed weekly catch records from 15 years of a standardized monitoring program to document the emergence of age-0 bigheaded carp in relation to environmental conditions. The appearance of age-0 fish was generally linked to hydrographic attributes, which probably serve as a cue for spawning. However, we found profound differences in the number of age-0 fish among years, which varied by as much as five orders of magnitude in successive years. The strong link between summer flooding and age-0 fish production we observed emphasizes the importance of understanding the hydrologic context in which sustained invasions occur. Despite evidence of sporadic recruitment, bigheaded carp populations in the Illinois River appear to be consistent or increasing because of particularly strong, episodic year classes.

Factors Regulating Year‐Class Strength of Silver Carp Throughout the Mississippi River Basin

“…For example, during 2009, a strong year-class of Silver Carp identified herein and during other studies within the Illinois River (Morgeson 2015;Stuck et al 2015) coincided with high river discharges. However, large yearclasses of Silver Carp in the middle Illinois River were also reported in 2008 (Gibson-Reinemer et al 2017) but not observed in this study, suggesting either that Silver Carp are not recruited into the adult population as age-0 fish or that mortality via commercial fishery harvest is effective at removing larger, older individuals from the population (i.e., Garvey et al 2012), precluding their capture throughout this study. Thus, although increases in discharge can promote stronger year-classes, Silver Carp recruitment can be successful under a wide range of environmental conditions.…”

“…However, large year‐classes of Silver Carp in the middle Illinois River were also reported in 2008 (Gibson‐Reinemer et al. ) but not observed in this study, suggesting either that Silver Carp are not recruited into the adult population as age‐0 fish or that mortality via commercial fishery harvest is effective at removing larger, older individuals from the population (i.e., Garvey et al. ), precluding their capture throughout this study.…”

“…; Lohmeyer and Garvey ; Gibson‐Reinemer et al. ). Thus, similar spatiotemporal variation in river conditions (i.e., long‐duration flood events) may synchronize Silver Carp recruitment throughout the Mississippi River basin.…”

“…Across native and invaded ranges, Silver Carp typically spawn in rapidly flowing river segments (thalweg habitats; 0.6-2.3 m/s) in conjunction with temperatures ranging from 18°C to 30°C (Verigin et al 1978). In addition, sudden increases in river discharge serve as a cue for Silver Carp spawning (Li et al 2006), and year-class strength (YCS) may be weak when these hydrological conditions are not met (DeGrandchamp et al 2007;Lohmeyer and Garvey 2009;Gibson-Reinemer et al 2017). Thus, similar spatiotemporal variation in river conditions (i.e., long-duration flood events) may synchronize Silver Carp recruitment throughout the Mississippi River basin.…”

Following the edge of the flood: use of shallow-water habitat by larval silver carp Hypophthalmichthys molitrix in the upper Mississippi river system

“…Additionally, a water level rise would increase the possibilities of larvae reaching productive floodplain habitats, including backwater lakes. On the La Grange Reach of the Illinois River, population dynamics of bighead carp Hypothalmichthys nobilis (Li et al 2009) and silver carp appear to be driven by sporadic spawning and recruitment linked to flooding (Gibson-Reinemer et al 2017).…”