Linking Adult Reproduction and Larval Density of Invasive Carp in a Large River

Abstract

Identifying how temporal variation in the environment affects reproductive success of invasive alien species will aid in predicting future establishment and tracking dynamics of established populations. Asian carp Hypophthalmichthys spp. have become a nuisance in recent years in the Mississippi River basin. Their populations are apparently expanding, indicating favorable conditions for reproduction. During 2004 and 2005, we quantified mean density of Asian carp larvae, mean monthly gonadosomatic index (GSI) of adult males and females, and number of eggs within mature females in the lower Illinois River, a major tributary of the Mississippi River. A flood (water velocity ≥ 0.7 m/s) and drought (<0.2 m/s) occurred during apparent spawning in 2004 and 2005, respectively. During 2004, Asian carp larvae were found during 32% of sampling weeks; mean GSI and fecundity were relatively low for adults, probably reflecting partially spawned individuals and perhaps low reproductive investment. During the drought of 2005, larval stages were present during only one (5%) of the sampling weeks, whereas mean GSI and fecundity of adults were high through summer. Females resorbed their eggs instead of spawning during this year. Spawning conditions during low water periods appear to be unsuitable for Asian carps, inhibiting adult spawning and yielding few larvae. Spawning conditions during 2004 were better but still yielded low densities of larvae relative to native fishes. Reproduction in the lower Illinois River appears to be linked to river flow and its impact on adult spawning decisions, but conditions for strong year‐class production (i.e., high larval densities) may be rarer than previously expected.

Recruitment sources of invasive Bighead carp (Hypopthalmichthys nobilis) and Silver carp (H. molitrix) inhabiting the Illinois River

“…O core values reflective of use of floodplain lake habitat rather than river channel habitat during early life. While age-0 Bighead and Silver carps commonly occur in floodplain lakes (Pegg et al 2002;Wang et al 2003;DeGrandchamp et al 2007), use of such habitats as nursery areas may be facultative for these species. Low-velocity nearshore and backwater habitats that do not differ in water δ 18 O from the main river channel may represent the primary habitats used by age-0 Bighead and Silver carps; these habitats are more extensive than River.…”

“…However, the relative importance of the Illinois, Mississippi, and Missouri rivers as natal environments and recruitment sources for Illinois River bigheaded carp stocks is unknown. As of 2013, bigheaded carps were known to be reproducing in the middle and lower sections of the Illinois River, the Mississippi River downstream from the mouth of the Missouri River, the lower Missouri River (unimpounded section), and pools 22, 24, and 26 of the upper Mississippi River (impounded section of the river upstream from the Missouri River confluence) (Schrank et al 2001;DeGrandchamp et al 2007;Lohmeyer and Garvey 2009;Baerwaldt et al 2013;Deters et al 2013). In the Mississippi River, larval bigheaded carp densities were substantially higher in pool 26 and the open river downstream from the Missouri River confluence compared to pools 22 and 24 (Lohmeyer and Garvey 2009).…”

“…In the Mississippi River, larval bigheaded carp densities were substantially higher in pool 26 and the open river downstream from the Missouri River confluence compared to pools 22 and 24 (Lohmeyer and Garvey 2009). Age-0 bigheaded carps have also been collected from connected floodplain lakes along the Illinois River (Pegg et al 2002;DeGrandchamp et al 2007); however, the relative importance of these floodplain lakes and low-velocity river channel margin habitats as nursery areas for Bighead and Silver carps is also unknown. A recently developed simulation model indicated that harvesting all sizes of Bighead and Silver carps is required to achieve fishery-induced collapse (Tsehaye et al 2013).…”

Assessment of otolith chemistry for identifying source environment of fishes in the lower Illinois River, Illinois

“…Restoration of river-floodplain lake connectivity may benefit both native and exotic fishes; connected floodplain lakes may be important source habitats for invasive Asian carps (bighead carp Hypophthalmichthys nobilis and silver carp H. molitrix) in the Illinois River (Pegg et al, 2002). However, Asian carps also spawn in the river's main channel (DeGrandchamp et al, 2007). Knowledge of the relative importance of the river channel and floodplain lakes to early life stages of Asian carps would be potentially valuable for developing strategies to control abundance of these exotic species that may be negatively affecting condition of native planktivorous fishes (Irons et al, 2007).…”

Placing the North American invasion of Asian carp in a spatially explicit context

“…During a drought year, adult Asian carp did not appear to reproduce in the lower impounded Illinois River (DeGrandchamp et al 2007), perhaps due to a lack of proper flow-related conditions. We hypothesized that the relatively unnatural flow regimes and perhaps impeded flow due to dams in the pooled UMRS, particularly during dry springs, might reduce Asian carp reproduction relative to unpooled southern reaches.…”