Sound frequencies detectable by grass (Ctenopharyngodon idella) and black (Mylopharyngodon pisceus) carp determined with auditory evoked potentialsa)

Grass (Ctenopharyngodon idella) and black (Mylopharyngodon piceus) carp were imported to the United States as biocontrol agents in aquaculture facilities; however, due to intentional stocking or accidental release, invasive populations have become established. Invasive bigheaded carps display negative phonotaxis to sound, suggesting acoustic deterrents as a potential management tool. Grass and black carp frequency detection in response to 0.2-6 kHz sound was evaluated using auditory evoked potentials (AEPs) and determined for sound pressure level (SPL) and particle acceleration level (PAL). AEPs were detectable in response to pure tone stimuli from 0.2 to 4 kHz. The lowest SPL thresholds for grass carp were at 0.3 kHz (87.0 ± 3.6 dB re 1 μPa SPLrms; mean ± standard deviation), and the lowest PAL thresholds were at 0.4 kHz (-65.8 ± 3.2 dB re 1 ms-2 PALrms). For black carp, the lowest SPL and PAL thresholds were at 0.3 kHz (93.4 ± 3.0 dB re 1 μPa SPLrms, -60.8 ± 1.5 dB re 1 ms-2 PALrms). These results indicate that the ranges of detectable frequencies for grass and black carp overlap with those reported for bigheaded carps. However, behavioral studies are needed to determine potential efficacy of acoustic deterrents for these fish.

Movement and behavioral states of common carp (Cyprinus carpio) in response to a behavioral deterrent in a navigational lock

BACKGROUND

Freshwater ecosystems are some of the most affected by biological invasions due, in part, to the introduction of invasive carp worldwide. Where carp have become established, management programs often seek to limit further range expansion into new areas by reducing their movement through interconnected rivers and waterways. Lock and dams are important locations for non-physical deterrents, such as carbon dioxide (CO₂), to reduce unwanted fish passage without disrupting human use. The purpose of this study was to evaluate the behavioral responses of common carp (Cyprinus carpio) to non-physical deterrents within a navigation structure on the Fox River, Wisconsin. Acoustic telemetry combined with hidden Markov models (HMMs) was used to analyze variation in carp responses to treatments. Outcomes may inform CO₂ effectiveness at preventing invasive carp movement through movement pinch-points.

METHODS

Carbon dioxide (CO₂) was recently registered as a pesticide in the United States for use as a deterrent to invasive carp movement. As a part of a multi-component study to test a large-scale CO₂ delivery system within a navigation lock, we characterized the influence of elevated CO₂ and forced water circulation in the lock chamber on carp movements and behavior. Through time-to-event analyses, we described the responses of acoustic-tagged carp to experimental treatments including (1) CO₂ injection in water with forced water circulation, (2) forced water circulation without CO₂ and (3) no forced water circulation or CO₂. We then used hidden Markov models (HMMs) to define fine-scale carp movement and evaluate the relationships between carp behavioral states and CO₂ concentration, forced water circulation, and temperature.

RESULTS

Forced water circulation with and without CO₂ injection were effective at expelling carp from the lock chamber relative to null treatments where no stimulus was applied. A portion of carp exposed to forced water circulation with CO₂ transitioned from an exploratory to an encamped behavioral state with shorter step-lengths and a unimodal distribution in turning angles, resulting in some carp remaining in the lock chamber. Whereas carp exposed to forced water circulation only remained primarily in an exploratory behavioral state, resulting in all carp exiting the lock chamber.

CONCLUSION

Our findings illustrate the potential of forced water circulation, alone, as a non-physical deterrent and the efficacy of CO₂ injection with forced water circulation in expelling carp from a navigation lock. Results demonstrate how acoustic telemetry and HMMs in an experimental context can describe fish behavior and inform management strategies.

Burmese pythons in Florida: A synthesis of biology, impacts, and management tools

Burmese pythons (Python molurus bivittatus) are native to southeastern Asia, however, there is an established invasive population inhabiting much of southern Florida throughout the Greater Everglades Ecosystem. Pythons have severely impacted native species and ecosystems in Florida and represent one of the most intractable invasive-species management issues across the globe. The difficulty stems from a unique combination of inaccessible habitat and the cryptic and resilient nature of pythons that thrive in the subtropical environment of southern Florida, rendering them extremely challenging to detect. Here we provide a comprehensive review and synthesis of the science relevant to managing invasive Burmese pythons. We describe existing control tools and review challenges to productive research, identifying key knowledge gaps that would improve future research and decision making for python control.