In spring, the Lusitano toad (Halobatrachus didactylus) suitors form choirs in the Tagus estuary in Portugal to sing the females’ serenade, vibrating their swim bladders to produce a call, known as a boat whistle, which resembles a vibrating cell phone. Males also listen to each other to check if someone is intruding on their territory. But unfortunately, their performances are no longer conducted in a hushed reverence. Spinning motorboats and spinning ferry propellers and engines fill the water with an unwelcome noise, which prompted Clara Amorim, Daniel Alves, Manuel Vieira and Paulo Fonseca of the Universidade de Lisboa, Portugal , to wonder if human noise pollution interferes with the ability of the talkative fish. communicate. They publish their discovery that the toad serenades are drowned out by sea traffic, which also disrupts their ability to hum together in Journal of Experimental Biology.
“We had already measured how far the toadfish could communicate with each other,” says Alves, who worked with a local fisherman to collect the vocal fish. Once the fish were comfortable in the lab, Alves and Fonseca tested their hearing by playing boat whistles – which had been recorded at distances of 0.1 to 15m – while recording the fish’s brain waves at the time. that they were listening to the sound against a silent background. Then the duo added the whine of an outboard motor or rumbling ferry and rechecked the brain waves, to see if the fish were still able to hear the serenades.
Unfortunately, the outboard motor almost completely drowned the male records. A boat whistle that had been clear up to 10.4m away in absolute silence became inaudible at distances over 2.5m and the range of another toad growl dropped to just 2, 0 m. However, the ferry appeared to have less of an impact on the toads’ hearing, reducing the range over which a boat whistle could be heard from 4m to 6.3m, while the other, which had been so severely affected by outboard motor, could be heard over slightly longer distances (6.7m). Vessel traffic clearly affects the ability of these vocal fish to hear each other, but does the sound of passing ships affect the harmonization of toadfish songs?
To find out, Vieira, Amorim, and Fonseca crossed the Tagus River to a quiet toadfish breeding ground, offering serenading residents 12 custom-built concrete nests, each equipped with an underwater microphone for recording. their boat whistles as they paired up with nearby males to attract females. In the still waters, neighbors coordinated well, advancing slightly or delaying their responses to each other’s calls depending on their proximity. However, when scientists passed recordings of ferries and motorboats to courting males, the toads’ coordination completely collapsed, with serenading duets more haphazardly interposed between the rumbles. timed from their neighbor.
“These results demonstrate that noise from boats can dramatically reduce the distance at which Lusitanian toads can communicate and affect the way they produce sounds in their choirs,” says Vieira, who warns that noisy human traffic could significantly affect life. in love with the Lusitano toad.
Study Confirms Ultra Music Festival Likely Stressful For Fishing
Daniel Alves et al, Boat noise interferes with the acoustic communication of the Lusitano toad, Journal of Experimental Biology (2021). DOI: 10.1242 / jeb.234849
Provided by La Compagnie des Biologistes
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