Movement patterns and habitat selection by Bighead Carp and Silver Carp within the lower Red River catchment

Abstract

Invasive species are one of the many threats facing native freshwater fish in North America. Invasive fish species can lead to population declines and assemblage-level changes among native fishes. Once established, invasive species are difficult to control and require well-informed management to mitigate their damage. By developing basic information on invasive species life histories and behaviors, managers can work better to minimize their negative effects. Bighead Carp Hypophthalmichthys nobilis and Silver Carp Hypophthalmichthys molitrix, (hereafter carp) are emblematic of this issue. Carp are characterized by high fecundity, an ability to tolerate a wide range of physicochemical conditions, and effective filter feeding. My study objectives were to determine the movement patterns and habitat selection by carp in the lower Red River catchment. I used active and passive acoustic telemetry technology to locate 50 tagged carp from March 2023 to August 2024. I used generalized additive mixed modeling to determine environmental conditions related to carp movement. Tagged individuals showed mobile and sedentary characteristics. The maximum distance recorded was 336 river-kilometers and a maximum rate of 38 river-kilometers per day. Carp also appeared not to travel outside of my study area in large numbers or travel to the western extent of my study. Carp moved at greater magnitudes during higher discharge variability. I also used a multistate model to estimate transition probabilities among habitats across unique environmental conditions. Carp were more likely to transition between habitats during times of increased water temperature and more variable discharge compared to times of low water temperatures and minimal flows. I modeled the variation in carp habitat selection using a resource selection function. Carp selected habitats that were deeper, had lower-velocities and which were out of the primary channel. This may be due to bioenergetic needs as these habitats require less energy to inhabit and contain higher food abundances. Management of these species must be context dependent as the lower Red River is different than other systems in carps invaded range. My results indicate that carp are making large movement within lower Red River that are consistent with conditions thought to cue spawning migrations. Removal efforts during less variable discharges and lower water temperatures would be the most effective as carp would likely be more congregated in specific habitats. Management targeting low-velocity areas that contain deeper water which are not in the primary channel would also result in more effective removal. Caution is warranted when conducting mitigation efforts as native fish could be inadvertently affected and compensatory responses could occur within carp populations.