Water guns affect abundance and behavior of bigheaded carp and native fish differently

Abstract

Water guns have shown the potential to repel nuisance aquatic organisms. This study examines the effects of exposure to a 1966.4 cm³ seismic water gun array (two guns) on the abundance and behavior of Bighead Carp Hypophthalmichthys nobilis, Silver Carp H. molitrix (collectively referred to as bigheaded carp) and native fishes (e.g., Smallmouth Buffalo Ictiobus bubalus). Water guns were deployed in a channel that connects the Illinois River to backwater quarry pits that contained a large transient population of bigheaded carp. To evaluate the effect of water guns, mobile side-looking split-beam hydroacoustic surveys were conducted before, during and between replicated water gun firing periods. Water guns did not affect abundance of bigheaded carp, but abundance of native fish detected during the firing treatment was 43 and 34% lower than the control and water guns off treatments, respectively. The proximity of bigheaded carp to the water gun array was similar between the water guns on and water guns off treatments. In contrast, the closest detected native fish were detected farther from the water guns during the water guns on treatment (mean ± SE, 32.38 ± 3.32 m) than during the water guns off treatment (15.04 ± 1.59 m). The water gun array had a greater impact on native fish species than on bigheaded carp. Caution should be taken to the extrapolation of these results to other fish species and to fish exposed to water guns in different environments (e.g., reduced shoreline interaction) or exposure to a larger array of water guns, or for use of water guns for purposes other than a barrier.

Appendices

Appendix: Methods

Stationary split-beam hydroacoustics sampling design

Stationary split-beam hydroacoustic sampling was used to examine the effects of water guns on the number of bigheaded carp and native fish detected per minute. Hydroacoustic data were recorded for seven consecutive days (July 21–July 28, 2013). While logistical difficulties (e.g., computer or software malfunctions) caused periods of interrupted data collection, efforts were made to collect data 24 h daily. Two treatments were used for this analysis: (1) a “water guns off’ treatment; and (2) a “water guns on” treatment.

Acoustic data were collected using four split-beam transducers (Biosonics DT-X portable, split-beam echo sounders (200 kHz, 6.8° dB beam angles) placed near the banks of the HMS channel, angled just below the water surface. Two transducers were placed on opposing banks approximately 15 m south of the water guns, with their beams orientated to slightly overlap. The two other transducers were situated similarly 15 m north of the water guns. Visual Acquisition (version 6.1, BioSonics, Inc., Seattle, WA, USA) was used to collect acoustic data. Data collection was set to begin at 1 m away from the transducer face to account for the near-field zone. The range of data collection was set to 50 m, which encompassed the entire sound beam prior to intersecting with the opposite channel bank. Prior to surveys, the water temperature was recorded and entered into Visual Acquisition to compensate for the effect of water temperature on the speed of sound and its absorption or reflection by targets. An initial on-axis calibration was performed on both transducers using a 200 kHz tungsten-carbide sphere.

Echoview (version 5.4, Echoview Software, Hobart, Tasmania, Australia) was used to estimate the number of fish targets detected per minute. Fish targets were determined using the single target detection algorithm for split-beam transducers (method 2). Fish targets were processed as fish tracks consisting of a minimum of two targets. Total length (TL; mm) of fish targets was estimated using an inverse of Love’s lateral-aspect target strength equation (Love 1971). Background noise and fish smaller than 280 mm total length were excluded from analyses by setting an acoustic threshold of − 31 dB. Fish greater than 528 mm TL were considered to be bigheaded carp, while fish 281–527 mm TL were considered to be native species.

Statistical analysis

All statistical procedures were performed using the SAS version 9.3 statistical package (SAS Institute, Cary, NC). Statistical significance was judged at α = 0.05. The effect of water gun firing on the number of acoustically detected bigheaded carp and native fish was examined using a Wilcoxon–Mann–Whitney test. Separate tests were used for each transducer.

Results

In total, 110,226 fish targets were detected during the 29,247 min of collected acoustic data, 31,410 of which were identified as bigheaded carp. Results from the Wilcoxon–Mann–Whitney tests revealed the water gun activity had no effect on per minute detections of bigheaded carp of native fish (Table 2).

Table 2 Results from Wilcoxon-Mann–Whitney tests to compare per minute fish target detections between water gun treatments