Light Trapping Reveals Multiple Bigheaded Carp Spawns Upstream of Lock and Dam 19 in the Upper Mississippi River

Abstract

The Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis are two species of invasive bigheaded carp currently invading North American rivers and watersheds. Bigheaded carp were accidentally introduced into the lower Mississippi River basin in the early 1970s and have since invaded many water bodies in the Midwestern United States. Evidence of bigheaded carp reproduction and recruitment in the upper Mississippi River upstream of Lock and Dam 19 (LD19) at Keokuk, Iowa, thought to be a critical constriction point to their upstream establishment, has been limited to a few isolated detections of eggs, larvae, and juvenile life stages since 2012. Therefore, a more comprehensive assessment of bigheaded carp reproduction in this critical management zone was needed. We used quadrafoil light traps (n = 1,387) deployed during May–September 2016–2018 in Pools 17–19 of the Mississippi River to monitor for advanced larval bigheaded carp in low‐velocity habitats. Throughout the sampling period, we captured 1,747 larval and 35 postlarval bigheaded carp (N = 1,782). Bigheaded carp were collected on 15 sampling events that spanned from May 31, 2016, to September 13, 2018, with associated hatch dates estimated to represent 10 unique reproductive events from May 2016 to September 2018. The individual captures and backdated hatch estimates revealed a protracted spawning period of up to seven events in 2016, one event in 2017, and two events in 2018. Bigheaded carp were only captured in Pool 19, possibly due to the drifting requirements for egg maturation and the low‐velocity downstream reach of Pool 19. This research provides confirmation that bigheaded carp spawned upstream of LD19 are capable of transitioning past the yolk sac stage upstream of this bottleneck to more advanced larval stages. Knowledge of reproduction and larval retention and the field‐based evidence of protracted spawning fill critical research gaps needed for the management of bigheaded carp.

Examination of Bigheaded Carp Ovaries Indicates Batch Spawning

“…In the UMR, approximately 20% of bigheaded carp collected in May and June did not have all oocyte stages present compared to fish sampled later in the year, indicating that development may continue throughout the summer. Our research (Lenaerts et al 2021) indicated that late developmental stages of oocytes per gram within spawning capable ovaries did not differ across ovary sections, but the proportions of different stages could differ within an ovary. The presence of multiple oocyte stages that have entered vitellogenesis and the presence of CA oocytes indicate that females are capable of producing several batches of eggs during a spawning period.…”

“…In the UMR and main tributaries, collections of drifting eggs and larval bigheaded carp support a protracted spawning period and multiple spawning events within a year (Larson et al 2017;Camacho et al 2021). During 2016, hatch dates of age-0 Silver Carp indicated 10 distinct cohorts (Williams et al 2021), and larval bigheaded carp captured in backwaters revealed seven distinct spawning events over 4 months in the UMR (La Hood et al 2021). Therefore, bigheaded carp may display flexible spawning strategies (Vilizzi 2011), including protracted or multiple spawning that may increase the likelihood of their successful reproduction in invaded ecosystems.…”

“…An approximately 0.5-g piece of preserved ovary with attached ovarian tissue was randomly biopsied and preserved in 10% neutral buffered formalin (Figure 2). Lenaerts et al (2021) found that the largest developmental phase of oocytes was not significantly different among the anterior, middle, and posterior sections of spawning capable ovaries; therefore, only one sample was collected per ovary. The tissue was placed in a disposable plastic embedding tissue cassette and then bathed in formalin prior to histological sectioning.…”

“…The UMR study area begins below Lock and Dam 16 at river kilometer (rkm) 736 (from the confluence with the Ohio River) and ends at Lock and Dam 20 (rkm 552). Fish were collected by commercial fishers contracted through Western Illinois University under the direction of researchers as an intensive removal effort in Pools 17-19 using gill nets and trammel nets set for a period ranging between 15 min and 24 h (length = 91.44-182.88 m, bar mesh = 8.89-12.7 cm, depth = 2.4-6.1 m; methods presented in Lenaerts et al 2021, this special section). Researchers used similar capture techniques in Pool 20, as well as using five-ring hoop nets (diameter = 1.52 m; mesh = 7.62-10.16 cm; throats on the first and fifth hoops) set for 24-78 h. Fish were targeted in tributaries and backwaters of the UMR based on known aggregations and telemetry data provided by the U.S.…”

“…Bigheaded carp are known to have multiple spawning events or an extended spawning period within a year based on egg collections (Wabash River; Coulter et al 2013Coulter et al , 2016Lenaerts et al 2015), the appearance of multiple young-ofthe-year size-classes (Illinois River; Gibson-Reinemer et al 2017), and larval fish collections (upper Mississippi River [UMR]; Larson et al 2017;La Hood et al 2021, this special section;Williams et al 2021, this special section). Bigheaded carp egg, larval, and young-of-the-year collections in the UMR have back-calculated hatch dates between May and August (Larson et al 2017;Camacho et al 2021;Williams et al 2021) and up to seven distinct spawning events (La Hood et al 2021), supporting the potential for batch or protracted spawning. In previous years, water temperature and hydrograph fluctuations in the UMR and major tributaries provided adequate spawning cues between late spring (April or May) through early fall (September or October; Camacho et al 2021).…”