Boat Motors Kill the Mood for Portugal’s Mating Toadfish, Study Finds

Lusitanian toadfish were the focus of a study that evaluated how much interference humans have on their underwater communication.

A Lusitanian toadfish (Halobatrachus didactylus) at low tide in the Tagus estuary, Portugal. (Credit: Clara Amorim)

(CN) — The male toadfish of Portugal are lonely. To put it bluntly, humans won’t shut up and all these sea creatures want is to get a word in. Such is the life of the Lusitanian toadfish.

These sea creatures rely on their ability to croon and serenade females by vibrating their swim bladders to produce a burp-like call. But boat motors and other man-made sounds drown out the harmonious chorus of these gregarious toadfish, according to a study published Tuesday in the Journal of Experimental Biology.

This isn’t the first example where humans have killed the mood for the animal kingdom.

Consider the Lusitanian toadfish: it’s a stocky, brown fish with dark spots, sometimes wading in tidepools. Study author Daniel Alves from the University of Lisbon, Portugal says they’re similar to the plainfin midshipman that live in the Pacific Ocean or the bony deep-sea anglerfish, though there’s no relation to the Lusitanian toadfish. What’s important to note is that the toadfish are auditory creatures and when outboard motors or a rumbling ferryboat pass by their breeding areas it nearly drowns out all of the breeding calls or as researchers refer to the boatwhistle, which is best described as a vibrating phone giving out a series of burps.

Alves originally focused his research on grasshoppers and cicadas, but made the switch to team toadfish after helping his colleagues in their field work. Previous studies on the toadfish studied how environmental factors affect their communication and how much of a role boats and other forms of noise pollution interrupt the underwater communication.

Researchers Alves, Clara Amorim, Manuel Vieira and Paulo Fonseca, all from the University of Lisbon, conducted the study on the effect of noise pollution on the toadfish population in Portugal’s Tagus estuary. With the help of local fisherman, researchers gathered their specimens. The research involved testing the brainwaves of the fish as they listened to the boatwhistle with a silent background and again with a noise background replete with motor boats.

One whistle was audible from around 34 feet away with a silent background, but that distance dropped to around 8 feet with the motor sounds and the sound of a rumbling toadfish was even less. A ferryboat sound had less of an impact according to the study authors.

When the toadfish are not the subjects of brainwave tests, they typically croon together in a toadfish symphony. Remarkably, their own calls duet with other males to attract females. Researchers wanted to understand if the boat sounds stepped over this toadfish concert and so 12 concrete nests were built that each had their own underwater microphone to record the boatwhistles. In a silent setting, these guys were able to achieve the toadfish equivalent of harmonizing, but when researchers played recordings of passing ferries and motorboats the coordination fell apart.

“These results demonstrate that boat noise can severely reduce the distance at which the Lusitanian toadfish can communicate and affect how they produce sounds in their choruses,” Vieira said in a statement.

Next researchers will conduct behavioral experiments on the toadfish said Alves to back up the findings in this study.

“I would also like to study different populations of this species to see if there are differences in their physiology related to the different environments in which they live,” Alves said in an email.

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