As shipping increases in the Arctic, it is changing Arctic cod behavior, new research shows, and those changes could have profound effects on the ecosystems and communities that depend on those fish.
When the researchers attached tags to the Arctic cod in Resolute Bay, Nunavut, they hoped to learn more about their behavior — how and when the fish feed, how they react to changes in the environment, and how they moved.
The tags were acoustic telemetry transponders, placed on the sides of the fish to measure their movements. The tags communicated with tracking stations placed underwater — a technology that can be very effective at showing exactly how fish are moving. It was the first time Arctic cod had ever been tagged that way.
But the researchers in Resolute Bay soon noticed a factor they hadn’t anticipated. As they worked, they saw ships coming in and out of the bay, and wondered what effects the ships’ underwater noise might have on the fish.
So the researchers tracked where ships were traveling within the bay and modeled how much sound they were likely making underwater. Then they overlaid patterns of fish behavior they recorded at the same time.
“We were actually pretty overwhelmed at what an impact those ships had coming into the sound and what it did to the Arctic cod behavior,” Aaron Fisk, one of the study’s authors, told ArcticToday.
Whenever ships were present in the area — whether they were moving or idling — the fish consistently stopped feeding or foraging for food and swam farther away, they found.
The researchers believe Arctic cod are sensitive to noise because they are preyed upon by beluga and ringed seals, and being able to detect sound likely helps them survive. “Probably these ship noises were perceived as a threat or danger to them, and they wanted to move away from them,” Fisk said. In addition, he said, background noise very likely impedes their ability to avoid their marine predators.
Arctic cod are one of the only forage fish in the region, so understanding their role in the ecosystem — and how it may be changing — is important, Fisk said. “They’re a conduit for energy and fat up to the sea birds and mammals and larger fish,” he said, and those animals’ “movements and behavior are keyed around trying to find Arctic cod and feeding on Arctic cod.” Other Arctic fish species also altered their behavior when ships were present, Fisk said.
This disruption, the researchers warned, has the potential to affect entire ecosystems — including the cod-dependent birds, whales and marine mammals upon which Arctic Indigenous communities depend for subsistence.
Fisk recalled a time when he was able to follow one of the gigantic schools of Arctic cod that stretched for miles.
“It looks like a big black oil slick of fish,” he said. He could see beluga and seals following and feeding on the masses of fish, while seabirds wheeled overhead. “When you impact Arctic cod, we know that it impacts the health of the animals that depend on it,” he said — and, in turn, those who depend upon those animals.
“Inuit food security may be affected if increasing ship traffic also disturbs Arctic cod near Inuit communities, contributing to exacerbation of an already existing food security issue,” said Silviya Ivanova, lead author of the study.
Fisk calls the potential change in Arctic fish behavior a “threat” to Inuit well-being, and the report highlights the broad implications “for all Arctic indigenous peoples’ subsistence and long‐term cultural traditions.”
The effects of shipping noise upon fish behavior has been documented in other parts of the world, particularly as ship traffic around the globe has quadrupled in the past three decades.
In the past, the Arctic was largely immune to such changes, since sea ice made it difficult to navigate northern waters. But Arctic shipping, including cruise‐ship traffic, doubled in the past two decades, the researchers point out — a “dramatic” increase brought about by the continued loss of sea ice. Now, marine species are exposed to more noise — and different types of noise — than they’ve been accustomed to in the past.
“It’s kind of virgin territory — a lot of those areas, ships couldn’t get into because of sea ice,” Fisk said. “These animals are very naive to the impact of what the ship noises are going to do.”
Such rapid changes will have “a very significant impact” on the food webs and the health of those who depend upon them, Fisk said. “Those food webs are breaking down and changing.”