Privacy Please: How Your Morning Commute may be Interrupting Fish Sex

We have all experienced that most irksome of annoyances: unnecessary noise. That car alarm going off at 2am, the not-so-quiet chatter during a test, basically anything your upstairs neighbors do. But for none has background noise been so arduous as for the Blacktail Shiner, a species of freshwater minnow.

“Stream” by Joshua Crauswell is licensed under CC 4.0

Stream” by Joshua Crauswell is licensed under CC 4.0

As it turns out, the Blacktail Shiners of the American southeast are going hoarse trying to yell over our human racket. Male Shiners produce sounds to attract mates and protect their territories. But the natural soundscape in which Shiners evolved is being tainted by traffic noise from overpass bridges. All this unnatural clatter is messing with the male Shiners’ game, as it prevents females from receiving and interpreting his mating calls. So those noisy neighbors we all hate? That’s us for the Blacktail Shiner.

Of course, nature is full of noisiness from both living and environmental sources. Many animals have worked around this natural clamor by finding ‘quiet windows’ in the spectrum of sound wave frequencies in which little noise occurs. Like with radio, species that use noise for communication find a free frequency slot in which to set up their own clear station. This is exactly what the Blacktail Shiner has done. But a recent study in Biological Conservation shows that traffic noise, specifically from semi-trailer trucks, interferes with the Blacktail Shiner station.

Researchers set up underwater sound recorders called hydrophones to record three different noise measurements: the natural ambient noise, human-caused background noises, and Shiner calls. Natural ambient noise was recorded near suitable breeding habitats in which Shiners could perform mating rituals. But most importantly, such habitats remained uncontaminated by human ruckus. When compared with Shiner calls recorded in the lab, the natural ambient noise did indeed show a gap where the Shiner frequencies fit in.

When traffic noises were added to the mix, the quiet window was no longer quite so quiet, as these frequencies overlapped with those of the Shiner calls. Outside noises infiltrating the quiet window that Shiners utilize means that these fish can no longer hear each other properly. Female Shiners can’t catch the sexy growls of viable suitors, and males may be less able to detect the ‘knocks’ produced by rivals near their nests. As Auburn University researchers Daniel Holt and Carol Johnston mention in their Biological Conservation article, “recovery to the natural soundscape may be as far as 12,113 m” from a traffic bridge. Just as with all other forms of pollution, the mal-effects of our noisiness spread far from the source.

But the male Shiners aren’t giving up so easy. Blacktail Shiners display a reflex known as the Lombard Effect. We’ve all experienced this effect before: when background noises get louder, we compensate by doing the same. Nature’s loudness fluctuates, and Shiners can deal with this by simply speaking up. So they should be able to do the same with human noise, right?

However, even with the Lombard Effect, traffic noise is making male Shiners look bad. The growls that males produce to attract females are made up of many different factors that each relay information about the male’s overall condition. For example, the duration of the growl seems to be correlated to the quality of the male. Females may choose to entertain certain suitors over others based on such quality parameters. But if traffic noise masks part of the duration of growls, females may move on without choosing a mate.

The issue of noise pollution doesn’t just affect Blacktail Shiners. Many other fish, some much more endangered, utilize quiet windows in similar ways. Our clamor could be detrimental to their reproductive success, especially since peak fish spawning times often overlap with morning rush hours. Co-author Carol Johnston warns that these “impacts, combined with others such as habitat degradation, can alter ecosystem function.  From a human perspective, this can impact ecosystem services such as water quality and important food fisheries.” So if we want these aquatic neighbors to stick around, we may need to keep it down.

Citation:

Holt, Daniel E., and Carol E. Johnston. “Traffic Noise Masks Acoustic Signals of Freshwater Stream Fish.” Biological Conservation 187 (2015): 27-33. Accessed September 14, 2015. http://www.sciencedirect.com/science/article/pii/S0006320715001494.

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This entry was posted in Conservation Biology Posts, Conservation Editorials 2015. Bookmark the permalink.

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