Blacktail shiners are little minnows with a black spot at the base of their tail fins. They’re also yellers: When it gets loud, the fish will raise their voices. But according to a new study published in Biological Conservation, even these vocal fish can’t hear each other when there’s too much traffic on the bridges over their streams. And it might be affecting their sex lives, Science reports. 

For an acoustic signal to be an effective source of communication, it must be detected and interpreted by the receiver. Male blacktail shiners (Cyprinella venusta) use acoustic signals to talk to other shiners: A growl for courting females, and a knock when fighting or defending against other males. These fish are pretty common in the southeastern U.S., and they prefer freshwater systems with rapidly flowing water. These are also noisy places. In addition to the sounds of ripples and waterfalls, there are anthropogenic sources that the fish didn’t evolve with: roads, train crossings, and boat traffic. 

Last year, Auburn University’s Daniel Holt and Carol Johnston discovered that the fish don’t get closer to each when there’s more background noise. Rather, they pump up the volume. Next, the duo wanted to study the relationship between blacktail shiner vocalizations and their natural soundscape—and how that’s being affected by bridges like those in the Tallapoosa watershed in Alabama.

The researchers dropped hydrophones into streams where shiners spawn to record the natural sounds in their mating areas, Science reports, and also to capture the reverberating sounds created by vehicles crossing bridges.

They discovered a link between a “quiet window” in the spectrum of their natural soundscape and the dominant frequencies of their courtship vocalizations. That means, like a few other fish, blacktail shiners have evolved the ability to pitch their mating sounds to exploit this window, Science explains. But noise generated from bridge crossings overlap with that window—in a way no natural sounds do—potentially masking their growls from a dozen kilometers (7.5 miles) away. 

The acoustic signals of blacktail shiners propagate short distances, and in urban areas, the propagation of traffic noise exceeds the range of shiner signals. With the prevalence of road crossings these days, entire watersheds are being impacted by this noise pollution.

[Via Science]

Images: shutterstock.com (top), Texas Parks & Wildlife Department (middle)