Summary
Recreational boating activity has the potential to generate noise pollution that may influence wild fish. Such noise may be particularly relevant to fish engaged in parental care (PC), where alterations in behaviour could influence individual fitness and productivity of fish populations.
Here, the PC behaviour of the freshwater largemouth bass (Micropterus salmoides) was examined to determine whether disturbance from boat noise altered paternal behaviour. Changes in nest‐tending and brood‐guarding behaviour were measured following exposure to noise treatments of 1‐min duration using underwater playbacks of recorded boat noises.
One experiment compared the behaviour of bass tending eggs before, during, and after exposure to high‐speed or idling combustion motors, or an electronic bow‐mounted trolling motor. No significant differences in the time on nest, number of pectoral fin beats, and number of turns between the pre‐treatment, treatment, and post‐treatment periods for all three motor types were observed.
A second experiment assessed the impacts of noise (high‐speed combustion motor only) on the behaviour of nesting bass across the development stages of offspring (i.e. egg, egg‐sac fry, and swim‐up fry). During the egg‐sac fry stage, nest‐guarding males turned significantly less on the nest during the noise treatment compared with the long‐term post‐treatment period, indicating a stage‐specific impact of boat noise on parental behaviour. The effect was transient, however, and limited to the period that the noise was present.
Given that PC and recreational boating activity tend to co‐occur in nearshore areas, prolonged or frequent repeated exposure of nesting fish to boat noise during the egg‐sac fry stage could have adverse consequences for fitness and reproductive output. Efforts to restrict recreational boating activity in the vicinity of fish engaged in PC (e.g. through the use of set‐backs) would be a risk‐averse approach to mitigating the effects of noise pollution on fish.
Methodology
Study site and species
Data collection occurred on Lake Opinicon in South Frontenac, Ontario, Canada in May 2016. Lake Opinicon is part of the Rideau Canal system, and contains several littoral regions with plenty of woody debris, providing a highly complex habitat for aquatic life (Figure 1; Crowder, Bristow, King, & Vanderkloet, 1977). Almost all boating activity on Lake Opinicon is recreational, including fishing, pleasure boating, water skiing, and canoeing (Graham & Cooke, 2008). Bulté et al. (2010) reported that ~5000 boats used the Rideau Canal locks at Lake Opinicon, but this number failed to incorporate ‘resident’ boats or those launched and removed on a transient basis.
Acoustic recordings and playbacks
First, recordings of three types of boat sounds were made at Lake Opinicon in an area with a mixed substrate (fines over gravel and rock) and a water depth of 6 m. The sound trap (300 STD hydrophone, 48‐kHz sample rate; Ocean Instruments Inc., San Diego, CA, USA) was anchored 2 m from the surface, and the boat (a 5.4‐m aluminium‐hulled fishing boat with a 75 HP Evinrude E‐Tec outboard motor; Evinrude, Sturtevant, WI, USA) passed by at a distance of 10 m from the sound trap. For the ‘high‐speed’ (HS) treatment, the boat made a single pass at high speed (operating at 5000 rpm); for the ‘idle’ (ID) treatment, the same boat passed by at an idle speed (600 rpm). For the ‘trolling’ (TR) treatment, the main engine was turned off and the same boat passed by using only the trolling motor (Minn‐Kota 75‐lb thrust trolling motor; Minn‐Kota, Racine, WI, USA). All sound files were truncated to a 1‐min duration to match the duration of the high‐speed pass‐by. As fishes are most sensitive to sounds below 1 kHz, all sound files were low‐pass filtered at 1 kHz; this also helped to remove unnecessary distortions from the underwater speaker at higher frequencies.