Noise-generating human activities affect hearing, communication, and movement in terrestrial and aquatic animals. But so far, direct evidence of impacts on survival has been scarce. An international group of researchers - Australian, Canadian and British - sought to examine the effects of motorboat noise on damselfish and studied their performance against their predators, pseudochromis fuscus.
A study on damselfish
The study shows that fish exposed to noise pollution from a motor boat were more easily caught by their predators. This situation is reversed when the fish are in their natural, unpolluted environment.
The noise of the motorboat stresses them and disturbs their reactions to their predator. They are more than twice as numerous to suffer from it. In laboratory tests, "prey" fish used 20% more oxygen in 30 minutes when exposed to motorboat noise. At sea, the results are the same since they used 33% more oxygen.
Stress that disrupts life
Researchers believe that this stress confuses the ability of prey to detect the arrival or presence of their predator. The passage of a motorboat near the fish would increase their reaction time to an enemy fish by 22%. They are therefore six times less likely to react to the arrival of their predator. This noise favors the predator, which needs 74% fewer attacks to capture its prey.
With the noise of a boat engine, the catch rate of damselfish in the laboratory is multiplied by 2.9 and by 2.4 at sea.
Motorboats increase fish mortality
This noise would therefore have a direct and negative impact on the prey since it increases its mortality. In places where motorboats are very present, such as the Great Barrier Reef, this could affect the demography of the impacted fish.
However, would getting used to the noise allow the damselfish to better bear it? Researchers don't know yet...
