Sources of Bighead Carp and Silver Carp Found in Chicago Urban Fishing Program Ponds

Abstract

Planktivorous Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix are two invasive species that pose a severe threat to native aquatic biota. Efforts have been made to inhibit Bighead Carp and Silver Carp expansion into the Great Lakes through hydrologically connected systems, but understanding their expansion to and from hydrologically disconnected systems could further reduce this risk. We assessed the origin of 23 Bighead Carp and 1 Silver Carp captured from Chicago Urban Fishing Program ponds using otolith chemistry. Otolith core δ18O and δ13C of captured Bighead Carp did not overlap with ranges of otolith δ18O and δ13C from Bighead Carp and Silver Carp from the Illinois River but was consistent with otolith δ18O and δ13C of Bighead Carp obtained from aquaculture facilities. Likewise, otolith core Sr:Ca of 19 captured Bighead Carp was higher than the range of otolith Sr:Ca from Illinois River Bighead Carp and Silver Carp. Due to inferred timing of introduction (likely age‐0 or age‐1 fish), these Bighead Carp may have been released incidentally via stocking sport fish shipments contaminated with the carp. Contrastingly, otolith chemistry results suggest that the captured Silver Carp originated from the Illinois River, although timing of introduction of this fish could not be inferred. Overall, our results indicate that nearly all fish analyzed did not originate from rivers within the Mississippi River basin and were instead likely introduced through stocking contaminated shipments of fish. Even though Chicago Urban Fishing Program ponds now pose a minimal threat for Bighead Carp and Silver Carp expansion into Lake Michigan, sustained urban pond monitoring and nonnative fish removal may limit or eliminate this alternative invasion pathway. Additionally, continued vigilance in understanding the origin of stocked fish and culture environment (e.g., polyculture) could decrease the likelihood of future invasive species introductions through contaminated sport fish stockings.

Patterns in spatial use and movement of Silver Carp among tributaries and main-stem rivers: Insight from otolith microchemistry analysis

“…We analyzed samples for Strontium (Sr), Barium (Ba), Magnesium (Mg), Calcium (Ca), Sodium (Na), and Manganese (Mn) at the University of Southern Mississippi's Center for Trace Analysis. Data were reported as the molar concentration for each trace element and converted to element:Ca (mmol/mol) ratios (e.g., Sr:Ca, Ba:Ca, and Mg:Ca) (Whitledge et al 2019).…”

“…We primarily focused on Sr:Ca ratios to classify the environmental history of Silver Carp. Strontium:Calcium ratios are commonly used in microchemistry analysis of Silver Carp otoliths (e.g., Norman and Whitledge 2015, Whitledge et al 2019, Love et al 2019. Speci cally, lapilli otoliths are analyzed for their Sr:Ca ratios because they are usually comprised of the aragonite polymorph of CaCO 3 (Whitledge et al 2019).…”

“…Strontium:Calcium ratios are commonly used in microchemistry analysis of Silver Carp otoliths (e.g., Norman and Whitledge 2015, Whitledge et al 2019, Love et al 2019. Speci cally, lapilli otoliths are analyzed for their Sr:Ca ratios because they are usually comprised of the aragonite polymorph of CaCO 3 (Whitledge et al 2019). Aragonite has a higher a nity for Sr compared to other polymorphs such as vatarite and calcite (Campana 1999;Melancon et al 2005;Pracheil et al 2019).…”

“…Ablations (beam diameter = 20μm, scan rate = 5μm/sec., laser pulse rate = 5hz) began approximately 100µm on one side of the nucleus, ablated completely thought the nucleus, to the adjacent edge of the otolith. We analyzed a standard developed by the U.S. Geological Survey (USGS) (MACS-3, CaCO3 matrix) every 15-20 samples to adjust for instrument drift using procedures outlined by Whitledge et al (2019). Otolith microchemistry data were converted to molar concentrations for each element and reported as element:Ca (µmol/mol) ratios (e.g., Sr:Ca, Ba:Ca, and Mg:Ca) using calcium as the internal standard and the stoichiometric concentration of calcium in aragonite Calcium Carbonate (CaCO 3 ) (Whitledge et al 2019).…”

“…Aragonite has a higher a nity for Sr compared to other polymorphs such as vatarite and calcite (Campana 1999;Melancon et al 2005;Pracheil et al 2019). A combination of Sr:Ca, Ba:Ca, and Mg:Ca ratios were used as an indicator for vatarite otoliths (Mg:Ca > 400µmol/mol, Ba:Ca < 4µmol/mol, and Sr:Ca < 100µmol/mol) (Whitledge et al 2019). We did not use Mg in any further reconstruction of environmental history because metabolic processes more heavily regulate Mg than Sr or Ba.…”