During summer in the early 1980s, a strange underwater noise plagued houseboat owners in Sausalito, California, just outside San Francisco. Against the backdrop of the Cold War, houseboat residents had suspected military activity or Russian submarines. But when the mystery was finally solved in 1985, the truth was perhaps even more surprising, given the “almost deafening” volume and mechanical quality of the noise: male toadfish looking for mates.
New research found that some two-thirds of ray-finned fishes, a branch of fish that comprises 99 percent of the world’s known fish species, have the ability to communicate by sound. Photo of foureye butterflyfish, one of the many species found to make sound, by Laszlo Ilyes.
Scientists and anglers have long known toadfish and a handful of other fish species such as catfish to be rather talkative. But new research reveals that the ability to make sound is a far more widespread trait among fish than previously thought. It turns out that nearly 29,000 species are likely to have the ability — with big implications for what we know about their lives.
“What our study shows is that with [fish sound production] being widespread, it starts to reframe how we think about sounds of the ocean,” says Aaron Rice, lead author of a new paper in the journal Ichthyology & Herpetology and a researcher at the K. Lisa Yang Center for Conservation Bioacoustics at the Cornell Lab of Ornithology. The clamor of the underwater world, it turns out, is likely just as diverse as it is in rainforests and wetlands.
The researchers conducted an analysis at the family rather than species level, mostly using acoustic recordings, knowledge of fish anatomy, and historical descriptions of fish sounds recorded by naturalists going as far back as Aristotle. Lacking vocal cords, fish make noise either by using their muscles to vibrate or drum their swim bladders (the gas-filled organs that help them swim at different depths without floating or sinking) — the most common method of sound production — or rubbing parts of their skeletons together. Rice and his coauthors found that these abilities had independently evolved at least 33 times within the class of fish. This tells us, says Rice, how “important” sound communication might be for fish, “and that there is a very strong selection pressure to use sound.” That is, factors such as predation or availability of food have meant that, for many species, fish who could produce sound stood a better chance of survival.
Though many fish sounds are yet to be recorded, Rice has been compiling a database of existing recordings for the past two decades. “That started as a side project, and then grew into somewhat of an obsession,” he says. He is excited to see similar efforts occurring elsewhere, such as the Global Library of Underwater Biological Sounds (or GLUBS), an international initiative to collect recordings of marine life sounds on a web-based, open-access platform. “Certainly within the bird-watching literature, there are these wonderful onomatopoetic descriptions of what different birds sound like. There’s plenty of birdsong CDs,” says Rice, “but nothing comparable has really existed for fish, and now there’s this revolution within the underwater acoustics world really bringing this attention back to fish and I think that’s really exciting.”
The new study also raises some concerning questions. If sound communication plays a role in how so many fish reproduce, defend resources, or avoid predators, then, says Rice, “the widespread extent of human noise pollution in the oceans may actually have some serious consequences with what it means for fish ecology.” The most ubiquitous source of noise is of course from ship traffic, but other noises such as far-reaching military sonar, tidal and offshore wind turbines, and seismic surveys for oil and gas exploration add to the underwater cacophony. The impact of this racket on marine mammals, including causing hearing loss, stress, and avoidance of noisy areas, is well documented, but what do we know about what it does to fish?
A 2018 review of 115 studies into human-caused underwater noise pollution catalogs a long list of harms to dozens of fish species, including “compromised communication, orientation, feeding, parental care, and prey detection, and increased aggression.” It can also “lead to less group cohesion, avoidance of important habitat, fewer offspring, and higher death rates . . . poor growth rates, decreased immunity, and low reproductive rates,” as well as hearing loss and abnormal anatomical development. To take a specific example, when exposed to boat noise, toadfish — like those bedeviling Sausalito’s houseboat community — struggle to communicate and find optimal mates, limiting reproduction and potentially affecting entire populations.
How are fish coping with increasingly noisy waters? We know that birds increase the volume and pitch of their songs to make themselves heard above traffic noise, but Rice says that fish “don’t seem to have that same level of plasticity.” He wonders if many fish populations have become “habituated” to increased noise pollution, and whether there are “chronic and sublethal impacts to these populations from increased ocean noise.”
Though noise pollution is already pervasive in the ocean, it could still get worse and reach new depths as marine industrialization increases, including through deep-sea mining. “We know so little about these deep-sea areas,” says Miyoko Sakashita, who campaigns for better legislative protections for marine life as the oceans director at the Center for Biological Diversity. “But it definitely seems like the mining itself, which is just scraping the bottom of the ocean, will be not only noisy but also destroy those deep-sea habitats.”
Currently, there is no international regulation of ocean noise pollution, though legislation to tackle the problem does exist at national and regional levels, such as the European Union’s Marine Strategy Framework Directive and the Marine Mammal Protection Act in the United States. The latter, says Sakashita, “is the one that’s been leveraged the most to have noise controls from activities like sonar and seismic.” In her view, the new evidence of fish acoustic communication being a common trait “could be important for increasing regulation of noise.”
NGOs and researchersa number of options for reducing ocean noise. For example, measures for ships could include technological modifications and reducing ship speeds. For an activity like pile driving — used to erect offshore wind turbines — acoustic barriers could be placed around the piling operation, while fewer, larger turbines could be installed to reduce the amount of pile driving required.
Noise isn’t the only threat to soniferous fish. The rate at which fish — being cold-blooded — contract the muscles around their swim bladders to produce sound, Rice explains, “is directly related to water temperature.” As water warms during spring and summer — fish breeding season — the fish start making noises at higher pitches. With climate change raising mean ocean temperatures and causing more frequent and serious marine heat waves, the question, says Rice, is what could “a persistent and directional change” in water temperatures mean for the fish?
In other words, if the oceans become consistently warmer, will fish keep having to raise the pitch of their calls, how will that affect things like reproductive success, and will they be able to adapt? New research modeling how climate change will affect the transmission of sound in the oceans adds another dimension to this concern; sound travels faster in warmer water, and there are certain “acoustic hot spots,” identified in the research that will experience significant sound speed variations later in the century due to climate change, with potentially big impacts on the species in those areas.
The growing evidence of fish sound production can certainly help scientists gauge the health of underwater ecosystems. “Being able to envision whether it’s a coral reef, or sandy bottom, or an estuary or a river as these vibrant, noisy places filled with fish sounds, this is what they should sound like,” says Rice. “[S]ound really is a critical component of these ecosystems, and something we should be paying attention to.”
These sounds, like the drone of the amorous toadfish, may not always be as musical as the more familiar songs of birds. But as the houseboat residents of Sausalito demonstrated when they launched the Humming Toadfish Festival in 1988, fish chatter is something that people could also learn to love and celebrate.
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