Do boats spook fish?

A friend was recently steelhead fishing on a Great Lakes tributary. He had just arrived at a productive looking run and had made a few casts before he noticed a group of canoes about to float over the best water. While rage was building up inside of him and he contemplated communicating his discontent with the canoers choice of route, he was surprised when a fish smashed his fly, right under the leading canoe. The take was unexpected because he had assumed the boats would spook the fish and ruin his chances, but it begs the question of how boats influence fish behaviour.

A team of researchers from Denmark recently addressed this question using an acoustic telemetry array in a private research lake. When combined with telemetry tags that were surgically implanted in individual fish, this array gave the researchers high resolution data of where fish were in the lake. The researchers studied the effects of power boating on the behaviour of three different species: Northern pike, roach and European perch. To test whether boating, or fishing primarily influenced these species, they either boated around the lake in short intervals (for 4 hours) or boated and casted artificial lures in between engine runs. The researchers then compared the movement and location of fish during these disturbances, to other days in which they did not boat on the lake.

The researchers found that boating did influence fish behaviour, although the response differed between different species. Both the European perch and the roach had increased swimming speeds during the boating periods, with the greatest increase in swimming speeds occurring at the start of the disturbance. Additionally, roach were more commonly found in the deeper, center of the lake during boating period than when boating did not occur. Neither species showed any difference in response in relation to whether the researchers just boated, or boated and fished, suggesting that it is boating itself rather than fishing that disturbs roach and perch. Also, Northern pike showed no obvious response to boating – they didn’t change the habitat they were found in and did not change their average swimming speed.

These findings not only have implications for anglers, but also for managers. If fish grow and reproduce better in certain habitats, but are chased out of those habitats by boaters, then boating could have a direct impact on fish populations. However, this study shows that boating will have different effects on different species, and so we might need to incorporate a species ecology (are they a predator or prey species? are they pelagic or do they primarily seek cover?) when thinking about how fish are influenced by boats.

Citation: L. Jacobsen et al. 2014. Effect of boat noise and angling on lake fish behaviour. Journal of Fish Biology 84: 1768-1780.

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