Using Otolith Chemistry to Determine Early Life Environments and Movement of the Emerging Bigheaded Carp Population in Pools 16–19 of the Upper Mississippi River

Abstract

Bigheaded carp (Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix) are invasive species in the USA and have spread throughout much of the Mississippi River basin. Population abundance upstream of Lock and Dam (LD) 19 (LD19) on the upper Mississippi River (UMR) has likely been limited by the high-head dam at this location, which restricts all upstream fish passage to the lock chamber. We measured otolith (lapillus) stable isotope composition and elemental microchemistry of 146 Silver Carp (n = 77 females, 69 males) and 141 Bighead Carp (n = 76 females, 65 males) to determine early life environments (ELEs) of adult bigheaded carp captured upstream of LD19 at the invasion front, in an area of intense management . Otolith oxygen isotope ratios (δ 18 O) and elemental ratios (Sr:Ca and Ba:Ca) were compared to values of isotope and elemental ratios in water from putative ELEs to assign the ELE for each fish. Most Bighead Carp (68.8%) and Silver Carp (54.1%) collected upstream of LD19 had otolith core signatures consistent with ELEs downstream of LD19. Nineteen percent of Bighead Carp and 34% of Silver Carp could not be classified. The sex ratios of bigheaded carp (Pools 17-19 combined) with otolith core signatures downstream of LD19 did not differ from 1:1. Our results, when compared to those of Whitledge et al. (2019), suggest low but stable recruitment above this population pinch-point dam in the UMR and suggest that targeting removal of bigheaded carp downstream of LD19 or inhibiting their movement upstream through the lock there might be effective as part of integrated control efforts.

Age‐0 Silver Carp Otolith Microchemistry and Microstructure Reveal Multiple Early Life Environments and Protracted Spawning in the Upper Mississippi River

“…Major tributaries and the main-stem UMR upstream of LD19 were distinguishable using a combination of water Sr:Ca, Ba:Ca, and stable oxygen isotope (δ 18 O) ratios (Whitledge et al 2019). In 2017, additional water samples were collected to verify the persistence of differences in water chemistry between the Mississippi River and tributaries documented by Whitledge et al (2019) and to characterize the water chemistry of backwater lakes and small creeks in the study area where age-0 Silver Carp were captured in 2016 (Anderson et al 2021). Two sets of water samples were collected during the spawning period (June-July) and again later in the summer (August-September).…”

“…An XSeries 2 ICPMS (Thermo Scientific, Waltham, Massachusetts) coupled with a Teledyne Photon Machines LSX-266 laser ablation system (Teledyne CETAC Technologies, Omaha, Nebraska) was used to analyze for 43 Ca, 86 Sr, 137 Ba, and 25 Mg and estimate elemental concentrations (beam diameter = 25 μm; scan rate = 5 μm/s; laser pulse rate = 20 Hz; laser energy level = 35%). A set of standards (i.e., NIST 1486 [National Institute of Standards and Technology] and MACS-3 [CaCO 3 matrix]) was run three consecutive times after every 12-15 samples to identify and correct for potential instrumental drift (Zeigler and Whitledge 2011;Whitledge et al 2019;Anderson et al 2021). We also used a 30-s gas blank prior to and following each laser ablation sample to account for background counts of elements.…”

“…Eight of those nine classes included a tributary, whereas the ninth class included only the UMR upstream of LD19. These categories do not completely match the categories defined by Whitledge et al (2019) or Anderson et al (2021) because of the additional water sampling by Anderson et al (2021) and our assumption that age-0 fish did not originate from early life environments downstream of LD19 (see Methods). Thirty-one (23%) of the 134 age-0 Silver Carp with otolith microchemistry data were classified in a category that included tributaries as early life environments, whereas 100 fish (75%) were classified into the UMR upstream of LD19 as the early life environment (Table 4).…”

“…Otoliths (lapilli) retain material throughout the life of the fish and can begin formation before the egg is hatched, therefore making them an ideal structure for microchemical analyses to discern environmental history (Campana and Neilson 1985). Otolith microchemistry has been used to infer early life history environments and spatial life history for bigheaded carp in the Illinois River (Norman and Whitledge 2015) and adult bigheaded carp in the Mississippi River (Whitledge et al 2019;Anderson et al 2021, this special section). Anderson et al (2021) and Whitledge et al (2019) revealed that adult bigheaded carp captured upstream of LD19 had early life environments located upstream and downstream from the dam, indicating that reproduction was occurring upstream from the dam and that bigheaded carp were moving through the dam.…”

“…Otolith microchemistry has been used to infer early life history environments and spatial life history for bigheaded carp in the Illinois River (Norman and Whitledge 2015) and adult bigheaded carp in the Mississippi River (Whitledge et al 2019;Anderson et al 2021, this special section). Anderson et al (2021) and Whitledge et al (2019) revealed that adult bigheaded carp captured upstream of LD19 had early life environments located upstream and downstream from the dam, indicating that reproduction was occurring upstream from the dam and that bigheaded carp were moving through the dam. Additionally, both studies provided evidence of tributary use during the early life stages of some bigheaded carp.…”