- Recreational boating continues to grow in popularity, yet little is known about the effects of noise disturbance from boating on fish. Therefore, this study evaluated the organism‐level cardiovascular disturbance associated with different recreational boating activities using largemouth bass (Micropterus salmoides) as a model.
- Cardiac output and its components (heart rate and stroke volume) were monitored in real time, allowing for the determination of the magnitude of disturbance and the time required for recovery. Fish responses to three noise disturbances (canoe paddling, trolling motor, and combustion engine (9.9 hp)) for 60 s were contrasted using a Latin squares design.
- Exposure to each of the treatments resulted in an increase in cardiac output in all fish, associated with a dramatic increase in heart rate and a slight decrease in stroke volume. The level of change in cardiac output and its components increased in magnitude from the canoe treatment to the trolling motor treatment with the most extreme response being to that of the combustion engine treatment. Furthermore, time required for cardiovascular variables to recover varied across treatments with shortest periods for the canoe paddling disturbance (∼15 min), the longest periods for the combustion engine (∼40 min), and intermediate recovery periods for the trolling motor (∼25 min).
- Collectively, these results demonstrate that fish experienced sublethal physiological disturbances in response to the noise propagated from recreational boating activities. This work contributes to a growing body of research that has revealed that boating activities can have a number of ecological and environmental consequences such that their use may not be compatible with aquatic protected areas. Future research should evaluate how free‐swimming fish in the wild respond to such stressors relative to frequency of exposure and proximity to noise as most research to date has occurred in the laboratory.
Nine largemouth bass were used for this study (Table 1). These fish were caught in May 2006 at Lake Opinicon in Elgin, Ontario, Canada (N 44º 33' 56.0" W 76º 19' 23.6"). Lake Opinicon is a shallow (mean depth=4.5 m) mesotrophic natural lake of moderate size (787 ha) on the Rideau Canal system and is regarded as a popular fishing destination.
Almost all boating traffic is recreational in nature and includes pleasure boating, canoeing, water skiing, and fishing. A wide range of boat types are used on the lake including canoes, small fishing boats (powered by both electric trolling motors and combustion engines), and larger pleasure craft. Fish were captured using standard angling gear and techniques. Once captured, the fish were held (for a minimum of 12 h before experimentation) in a water-flow-through holding tank (150 cm × 62 cm × 55 cm) that was continuously supplied with fresh lake water, at the Queen’s University Biological Station. All of the methods used in this study were approved by Carleton University’s Animal Care Committee (Protocol B06-02).
The surgical procedure used in this study follows that described by Cooke et al. (2003a), and is briefly outlined below. Using three fish per treatment day, each fish was individually introduced to a bath containing a solution of water and 60 mg L-1 of clove oil (emulsified with ethanol in a 9:1 ratio of ethanol to clove oil). This solution was used to anaesthetize the animal to a point where equilibrium was lost (approximately 5 min). The fish was then placed on a wet sponge on the operating table where a solution containing 30 mg L-1 of clove oil (maintenance dose) was pumped over the gills to ensure that the fish remained anaesthetized. The gills and operculum of the fish were held back using a plastic oval shaped cover which was placed behind the first gill arch to provide unimpaired access to the aorta.
Using a pair of blunt forceps, the connective tissue surrounding the ventral aorta was carefully removed. A Doppler flow probe (sub-miniature 20 MHz piezoelectric transducer: Iowa Doppler Products, Iowa City, Iowa) was selected for each fish based on the diameter of the aorta. The sizes of the flow probes varied from 1.2 to 1.6 mm. The cufflike silicon probe, once checked for sufficient signal strength, was placed onto the aorta and held in position by a single suture. The lead wire attached to the probe was sutured three times to the exterior of the fish to ensure that the cuff remained in position during any fish movement.
To monitor cardiac output, a flow meter (545C-4 Directional Pulsed Doppler Flowmeter: Bioengineering, The University of Iowa, Iowa City, Iowa) and a digital strip-chart recorder (LabVIEW, version 4.0.1, National Instruments Corporation, Austin, Texas) were used. The procedure took approximately 30 min for each fish and was repeated for two more fish on each treatment day to give a total of three fish per trial. Following surgery, the three fish were given approximately 12 h to recover in individual chambers located in an undisturbed experimental tank (150 cm × 62 cm × 55 cm). The experimental tank was continuously supplied with fresh lake water. The fish were considered to have ‘recovered’ from surgery once they displayed normal cardiac output, a period of at least 6 h (Cooke et al., 2003a). Cardiac parameters of the fish were recorded for several hours before treatment and for several hours post-treatment.