As an underwater acoustician, Rosalyn Putland researches underwater sounds, asking how human sounds might impact the creatures living in the world’s waters. When she moved from New Zealand to Minnesota three years ago, she shifted her research from oceans to freshwater lakes. She has studied fifteen small lakes in St. Louis and Carlton counties. Agate Magazine recently noted an article about her work in Great Lakes Echo, and we asked Putland to describe her work and its implications for the health of lakes in northeastern Minnesota.
Agate: How did you get interested in learning about small lakes?
Putland: I was helping with the field work in an ecology class at the University of Minnesota Duluth. The professor asked me to bring a hydrophone to show students how to record underwater. After we got back, we listened to the sounds, and we started to dig out the fish sounds, to distinguish them from other sounds in the lake. And it gave me the idea that this hasn’t been recorded before. Sometimes research springs upon you: just by chance you come across something that seems exciting and you want to develop it further, and that’s what happened with this freshwater lake research.
Agate: Tell us about the process of recording in a lake.
Putland: When we’re out on a lake in the winter, it looks like we’re ice fishing: we drill a hole through the ice and put the hydrophone (that’s a microphone that detects sound waves under water) down. Everything must be waterproof of course, and it’s plugged into a recording system. When we get back to the lab, we do our data analysis. We’re also using cameras to record fish behavior and to try to correlate the recorded sounds to what the fish are doing. Putting a camera underwater is challenging: under the ice there’s less light, so we add lights, we use bait, and we have to calibrate the system in order to judge distances. We use equipment that’s temperature-tolerant; otherwise, when we brought it up, it would freeze. And we can’t leave it out for long.
Agate: How do animals underwater use sound?
Putland: There are basically three groups of animals in Minnesota’s lakes: fishes, invertebrates, and mammals. I study fishes, and they use sound to navigate, to find food, and to avoid predators. It’s the same as people walking on the street. When you hear a sound, you turn around to find out what it is. Invertebrates have also been found to use sound. Mammals, such as beavers and others, could also be using sound.
Agate: How do fish hear, and do some fish use sound more than others?
Putland: Fish have otoliths, small bones in the inner ear. These are solid, so they move more slowly in response to sound waves than the rest of the fish does. That difference bends hair-like structures in the inner ear, and the fish’s brain interprets that as sound. Any fish that’s been tested for hearing has been found to react to some form of sound. There’s more known about the marine environment than freshwater systems. At the lab at UMD, we test the hearing of native fishes: bigmouth buffalo and lake sturgeon. How they use sound seems to depend on their feeding strategy: the predatory fish use it to find food, and the prey fish use it to avoid predators. The benthic fish, the ones that live along the lake bottom, can feel the sound through the solid bottom of the lake as well as through the water column.
Agate: Do they use it in mating?
Putland: Some fish, such as burbot (or eelpout) have been thought to use sound for mating. In the open ocean, cod use sound to spawn, to attract each other. Some fish use sound when guarding eggs. It’s one of those things: the more we record and can link sound to specific fish behavior, the more we find out.
Agate: What does it sound like down there? What do you hear when you’re sitting out on the ice?
Putland: It often sounds pretty silent. We’re very fortunate in Minnesota; we still have a relatively pristine sound environment. We hear a lot of ice cracking, which is really eerie. It’s a high frequency sound like the lightsabers crashing against each other in Star Wars. Then there’s the popping and grunting of fish species: carp like bigmouth buffalo make grunts or growling sounds. When humans are present it’s much, much louder: there’s boats in the summer, ice augers and walking on the ice in the winter. Those sounds are comparable to a construction site on land.
Agate: So, do you think those sounds are harming the fish?
Putland: Our hypothesis is that the sounds we’re introducing could be changing fish behavior: maybe they move away from the noise, into shallower or into deeper water. They could just be moving away from the sound, like people crossing the street at a construction site. We’re also wondering if human sounds disturb activity or feeding during reproductive periods. Now we’re putting cameras down to see. There are also concerns about possible hearing damage if the noise gets really intense; that would be something like building a harbor, installing a dock platform.
Agate: Drilling a well?
Putland: Yes, it’s the same as if you’re drilling an oil platform out at sea. There’s a lot of concern, especially with marine mammals, about how human activity might be impacting them. In freshwater, we don’t have glamorous whales and dolphins, but now this sound can be considered a type of noise pollution. Are we polluting our environment with sound rather than oil spills and chemical pollution and things like that?
Agate: Do we know what happens over time, for instance, do lakes that have a lot of human impacts lose fish?
Putland: The question is, do fish get desensitized, like people living under an airplane route? The theory is that fish in heavily used lakes might learn to ignore the sound. We’re starting to do lab experiments now, exposing fish in tanks to human sounds, testing their hearing and behavior after the exposure. If there’s an impact, that could be key information for lake managers and policy makers.
Agate: Aren’t resource managers using sound to try to keep invasive carp from spreading?
Putland: Invasive carp have been studied quite heavily for their hearing ability, with the idea that you can put sound systems underwater and prevent them from moving up the rivers toward the Great Lakes. These systems generate sound and particle motion that seem to irritate carp, so they tend to turn around and swim away. They do have a sensitivity to hearing; you’ve seen the videos of big carp jumping into the air. The big question in my mind is, if you’re putting sound in an environment to stop invasive carp, what about the native fish in the area, and in particular the ones we’re interested in fishing?
Agate: What other research is needed to understand the situation better?
Putland: I like getting data from different environments and different times of year, so a lot of what I’ve done is comparing summer to winter; it would be nice to know how sound changes in spring and fall as well. And then scaling it up to the bigger lakes: what’s going on in Lake Superior and the other Great Lakes? We have the effects of shipping, we have massive cargo and container vessels coming in and out of the harbor, so what’s going on in the fish populations? But studying Lake Superior is full of challenges. I have deployed some equipment for two winters now: you put it out there in September, and can’t get it back until April or May, and then you have terabytes of data to analyze! I compare the recordings with shipping activity: I get the shipping logs from the Coast Guard and other sources so I can see the movement of vessels and how loud things are; I can also compare it to small lakes.
Agate: Help us understand the importance of your work.
Putland: I guess the biggest thing to know is that sound can be as critical for underwater animals as vision is for us. We can see what’s going on in our environment; if you’re underwater and it’s murky, it’s dark, muddy, anything like that, you really are relying on sound. I like to think that I’m listening to this underwater orchestra, with all the sound going on. Each animal or each fish species has its own role to play in the orchestra, its own part to play in the little symphony that’s going on underwater.
RosalynPutland has conducted underwater acoustic research in New Zealand and Minnesota. Her research focuses on the impacts of human activities on the sound environment of fish. Her research has been published in various scholarly journals, including Global Change Biology, Reviews in Fisheries Biology, and Ecological Indicators. She is currently a Post-Doctoral Associate at the University of Minnesota Duluth.