By Doreen Leggett
Decades ago, fishermen knew if they wanted to catch cod they were better off in a skiff; the bearded fish didn’t like the sound of motors.
Years later, the ocean is noisier and scientists are learning how that affects the marine ecosystem.
Aran Mooney, an associate scientist at Woods Hole Oceanographic Institution, has worked on the impact of noise in the ocean for close to 20 years. Then the focus was on Navy sonar, now it’s wind turbines. With one wind farm being built offshore, and seemingly more to come, there are concerns about the fisheries.
“Fishermen told BOEM (the Bureau of Ocean Energy Management) they needed to start studying these issues,” said Mooney, who works in the Sensory Ecology and Bioacoustics Lab.
Mooney and others exposed scallop, squid and black sea bass to a range of sounds and frequencies and studied the responses. One of the most worrisome finds is the behavior of young scallops, which closed when researchers subjected them to recorded noise of wind farm construction. The study used pile-driving acoustics and vibrations for 15 minutes on, and 15 minutes off, for four hours.
“They are kind of holding their breath,” Mooney said. “Scallops are the most dramatically affected.”
“Being constantly subjected to noise means scallops are constantly closing their valves, expending energy and reducing their oxygen intake,” the study states. “While further research is needed to quantify the effect this has on scallop populations, noise pollution could stunt their growth and leave them vulnerable to predators.”
Scallops can move, but usually only once a day, and it is taxing.
In addition to scallops, Mooney and others have been looking at squid and sea bass. The effects on longfin squid have been obvious.
“We played pile-driving (sounds) and the squid inked and changed (movement) patterns,” said Mooney.
The squid seemed to recover quickly, bouncing back in 30 seconds.
The team ran other tests, measuring how many times the squid jet or fin when subjected to pile-driving.
The studies, published for BOEM in 2023 by Jenni Stanley, Mooney et al, are the first to demonstrate behavioral effects of pile-driving noise on any cephalopod species, focusing on commercially important squid; their range overlaps areas where marine construction projects are projected.
All squid exposed to pile-driving noise responded with alarm behaviors — inking, jetting and pattern change.
The squid generally also had lower prey capture rates, and were more likely to abandon pursuit of prey if noise started, the study stated. Initial work was done in tanks, with follow-up in the water off the WHOI pier.
Squid seemed to adapt to the noise better than scallops. The inking, and avoidance, didn’t seem to “be hugely energetically consequential” and the squid went back to normal behavior.
“Their brain seems to be wiped clean,” said Mooney.
Questions remain as to whether noise would be more disruptive if squid are focused on a task – either chasing prey or swimming from prey.
Mooney said squid occupy a pivotal spot in the food chain, and are prey for economically important fish, such as bluefish, flounder and tuna. The long-finned squid has had annual landed values of about $30 million since 2010, according to National Marine Fisheries Service.
Researching black sea bass was more complicated. What researchers realized right away is sea bass can hear. That may seem obvious, but earlier work has shown disparities on land and on the sea: Moths can hear bats coming, but squid can’t hear dolphins bearing down.
When the team began their experiments on black sea bass they got the fish acclimated in large tanks for a year before introducing noise. The effect was immediate.
“They are up in the water column and when the pile-driving starts they go sit on the bottom,” Mooney said. “When you scare a fish they aren’t going to eat. They should be eating a lot.”
Growth and reproduction can be inhibited with negative consequences on the stock and therefore fishermen and a growing industry. Earlier work had shown that sea bass were most sensitive to the frequencies created by shipping and underwater construction, but pile-driving hadn’t been studied.
“Added sounds humans are emitting into the marine environment could potentially have a wide range of effects on commercially important fish species, with exposure to very intense or loud sounds resulting in damage to hearing structures, body tissues or even death. However, more importantly are the associated issues with sound and the potential to affect an animal’s behavior that could also result in effects on populations and ecosystems,” the study states, noting that noise in the ocean can travel almost five times faster than on land.
Also on the minds of researchers and commercial fishermen is that black sea bass move through offshore areas. Construction noise, and the wind energy areas themselves, may affect this migration.