Boat noise affects some fish a lot more than others

Posted on October 15, 2015

Although it’s known that artificial underwater noise can disrupt the behaviour of fish, there have been few detailed studies on this topic in freshwater environments. Researchers collected comparative information on the responses of three common fish species (roach Rutilus rutilus, perch Perca fluviatilis and pike Esox lucius) to boat activity in Lake Gosmer, a small (0.9 ha) lake in Denmark. They set up eight hydrophones around the lake, each positioned one metre below the surface of the water, and recorded the movements of 21-23 individuals of each species for four weeks in September-October. Every third day, disturbance was created by turning the boat engine on, moving the boat for 1-2 minutes, mooring the boat, turning the engine off, and repeating this procedure every 15 minutes over a four-hour period. The previous day, when there was no disturbance, was treated as a control period. The behaviour patterns of the three fish species were distinctly different. Throughout each disturbance period, roach increased their swimming speed by 5-8 times each time the engine was restarted, avoided areas where the boat was moored, and gathered in the middle of the lake. In contrast, perch increased their swimming speed (by 2-4 times) only in the first hour of disturbance, didn’t react sharply when the motor was used, and didn’t change their pattern of distribution. And pike showed no significant change in behaviour in response to boat noise. These results support the prediction that relatively small prey species (such as roach and perch, measuring 16-24 cm in length in this study) are more likely to show alarm responses than large predator species like pike (49-99 cm).
The strong response of roach, a cyprinid species, was consistent with the fact that cyprinids have particularly sensitive hearing. It seems likely that boat noise has a significant effect on the energy consumption and habitat use of at least some species of freshwater fish.

Reference: Jacobsen, L. et al. 2014. Effect of boat noise and angling on lake fish behaviour Journal of Fish Biology 84, 1768–1780. viour