ENVIRONMENTAL DRIVERS OF HABITAT USE BY BIGHEADED CARPS TO INFORM HARVEST IN THE STARVED ROCK POOL OF THE ILLINOIS RIVER

Lateral habitats provide a multitude of benefits to riverine fishes, including invasive Silver Carp (Hypophthalmicthys molitrix) and Bighead Carp (H. nobilis), hereafter bigheaded carp. Harvesters have focused removal efforts in lateral habitats (e.g., backwaters and side channels); however, little research has examined the lateral habitat use of bighead carps. The Starved Rock Pool (SRP) is the downstream most pool in the upper Illinois River where contracted commercial fishermen target bigheaded carp to reduce dispersal pressure towards the Laurentian Great Lakes. To examine bigheaded carps’ movement between the main channel and lateral habitats in SRP, fish were implanted with transmitters and tracked using acoustic telemetry. The ranges and detection probabilities of acoustic telemetry receivers have typically been modelled and examined in with linear distance tools. To derive more realistic receiver ranges and detection probabilities, this study used minimum bounding geometry on detected transmissions obtained from boat-mounted transmitters. Receiver detection ranges estimated using minimum bounding geometry were smaller than those estimated using the linear distance method, but estimated detection probabilities within receiver ranges were higher using the minimum bounding method compared to the linear distance method. Detection histories of bigheaded carp implanted with transmitters were examined to assess fish habitat use from June 2016 to April 2018. During 2017, multiple environmental variables (temperature, river discharge, chlorophyll a, dissolved oxygen, total dissolved solids, and turbidity) were measured weekly and zooplankton samples were collected during June and August to assess potential associations between environmental variables and bigheaded carp habitat use that might be useful for informing locations and times for focusing contracted harvest of bigheaded carps. Habitat selection was also examined using a resource selection index (W) and a mark-recapture multistate model in program MARK. Across all seasons, bigheaded carp used lateral habitats more frequently than main channel habitats. Habitat use was strongly influenced by temperature and marginally by main channel discharge. No strong associations between zooplankton and bigheaded carp habitat use were observed during this study; however, there were some differences in zooplankton community structure and abundance among lateral habitats related to rotifers that may have potentially been related to use of specific lateral habitats by bigheaded carp. While having high return percentages to all lateral habitats, bigheaded carp disproportionately selected for a few individual habitats, possibly due to those habitats being locations where tagging was conducted. Harvest efforts in lateral habitats, especially prior to spawning (spring staging), during lower temperature periods (overwintering), and during higher discharges should be most effective because of bigheaded carps’ particularly high use of lateral habitats during these times. Recurring removal efforts in lateral habitats within SRP may facilitate targeting of individuals that frequently return to these lateral habitats and may also reduce bigheaded carp abundance in nearby locations