What do noisy oceans mean for fish?

Picture this: It's Monday morning, and you wake up groggy to your alarm because the incessant traffic and blaring of truck horns from the local highway kept you from getting a good nights' sleep. You'd go back to sleep, but your spouse is already up watching TV and that annoying anchor for the 6 AM news is peppily rambling about how great his week abroad in Hawaii was - like an image of him in a speedo is what you need in your head first thing.

You hop in the shower, if only to drown out the television, and try and remember what exactly it was that you were supposed to do before work this morning over the rush of the water. But you can't focus - you're exhausted and unable to think clearly. Suddenly, the smoke detector goes off because your breakfast is burning, and in the momentary panicked response to the high pitched siren invading your thoughts, you run naked out of the house - just as the local school bus happens to be coming down the street. Alert to the rising humiliation, you rush back inside, and end up fiddling with the detector for ten minutes trying to take out the battery while you can feel the siren resonating in your bones and bringing on a terrible headache you know won't go away easily. All this, you think, and you just started your day.

What ruined your morning? Noise. All kinds of different, invasive noises - the cars at night, the alarm, the TV, the shower, the siren - all these noises affected your ability to sleep, think and focus. The ambient noise can take a toll on your mind and body, let alone the immediate effects of a loud, inescapable sound like the smoke detector. Noise is stressful; it's no wonder we like to vacation in the quiet, remote places that still exist.

Unfortunately, the fish in our oceans don't have that luxury. Unlike we might think, our oceans are a hotbed of noisy activity. Shrimp snap their claws, dolphins whistle and click, and a variety of animals make strange and unique noises to hunt and communicate. However, as humans began to conquer the seas, a new set of sounds came into play. Navy sonar, boat engines and a host of other human activities create quite a ruckus underwater. But how much do our noises impact the ocean's creatures? That question is exactly what Arthur Popper and Mardi Hastings sought to answer in their recent review article "The effects of human-generated sound on fish" published this month in Integrative Zoology.

They looked at the research to date on how anthropogenic (human-created) sound affects fish - slim pickings. There haven't been too many good, detailed studies which look at how fish respond to sounds. Many simply try to find threshold hearing levels under quiet conditions. But the ocean is never quiet, and lab-generated thresholds tell us little about how noises affect behavior or health in the real ocean. We have looked at it in marine mammals - and the results aren't promising - but somehow the less cute and cuddly 'sea kittens' (as PETA would say) just haven't been researched well. What we do know is damning.

The first and most obvious effect of sound on fish is the affects of loud, intense blasts like those caused by sonar or seismic exploration. If a sound is loud enough, the pressure created by its wave can damage tissues - this can happen to people on land, not just fish in the oceans. In general, though, we don't create blasts loud enough to rupture vessels and cause hemorrhaging in our own habitats. Sonar and seismic activity have been blamed for fish kills and marine mammal standings all over the world.

But death isn't the only, or necessarily even major, affect of these sounds. Studies have found that loud noises from seismic guns can damage the hearing physiology of fish far enough away to survive, even render them deaf, if only temporarily. If species use sound to warn of approaching predators or to search for mates, the ecological effects of these sounds could be substantial at a much larger radius than the imminent kill zones.

It's not just the ecology we have to think about - we are commercially harmed by these effects. Studies have shown that the catch for commercial species like haddock and cod following seismic exploration decreased dramatically, and didn't rebound for almost a week. Researchers have observed fish actively avoiding loud noises, which might have big impacts on fishing in areas near noisy ports or naval test sites.

Larval fish are especially vulnerable. Their soft, small bodies don't withstand the same levels of sound that the adults do. Some studies have found increased mortality in fry exposed to loud noises, but overall there is a lack of research on the effects. If we're killing or disabling the fish young, they can't keep their population numbers matching our ever increasing demand.

The authors note that there is one area that truly lacks research - sustained effects of background noise on wild populations. While humans and other animals show increased stress and even behavior changes when exposed to high levels of ambient noise, little to no research has looked at the effects of this kind of noise on fish. Lab studies have found that increased background noise can causing temporary or even permanent hearing loss in fish, but to date no one has looked at how this loss might effect the ecology or behavior of wild individuals.

The guess is that long exposure to high levels of ambient noise has the same effect on fish that it does on humans - it sucks, colloquially speaking. It's stressful, affecting their hormones, health, and even ability to function properly. Just like it's hard for you to flirt with a hot chick in a noisy club, it might be hard to fish to find a mate in a noisy reef or tell his buddies that there's a shark on the prowl for tasty morsels. The eventual effect of which is slowed or stopped reproduction, productivity, or even ecosystem shifts due to some species managing better than others in the loud environment. Studies have already shown some species are more susceptible than others.

This research is getting more and more important, as increasing human populations have us hunting further and further from shore for food and oil and upping shipping traffic. And as if the direct increase in human activity weren't bad enough, we're increasing the noise in the ocean another way - by our carbon emissions. As we produce more and more carbon dioxide, we alter the pH of seawater, making it more acidic. In acidic waters, low frequency sounds like boat engines and motors travel further. We might amplify the range of our acoustic effects by 20% or more because of ocean acidification in the next fifty years.

Which, of course, is bad news for the fish, especially those in the highly productive estuaries close to shore where we tend to get a little noisy. And what's bad news for fish is bad news for us - we depend on those ecosystems for food, tourism and other natural products. If we can't find a way to lower the volume, we may find our oceans end up a bit quieter that we might like.

POPPER, A., & HASTINGS, M. (2009). The effects of human-generated sound on fish Integrative Zoology, 4 (1), 43-52 DOI: 10.1111/j.1749-4877.2008.00134.x