When Carnival Corporation ships sail into Glacier Bay National Park and Preserve, a protected area teeming with wildlife and striking landscapes, they go into quiet mode.
The vessels don’t make any announcements on outside weather decks, and they also slow down from between 14 and 18 knots – between roughly 16 and 21 miles per hour – to often less than 10 knots.
That way, passengers can see animals like seals lounging on bergy bits, while the ship minimizes disruptions to the marine environment.
“Most often, the ship can transit in a place like Tracy Arm or Endicott Arm or Glacier Bay, and typically we don’t see any of the seals move at all,” said Patrick McGuire, vice president of environmental operations and policy for the company’s Holland America Group, which is comprised of Holland America Line, Princess Cruises, Seabourn and P&O Cruises Australia. “So, that’s certainly our objective is to not have any noisy interference with marine mammals because that’s what everyone comes to see.”
Those kinds of measures are among a number of steps cruise lines have taken to reduce noise pollution from their ships, which has become a point of increased focus in recent years for many cruise lines.
How do cruise ships create noise pollution?
Sound is a common sensory modality for animals underwater, according to Dr. Leila Hatch, Research Ecologist with NOAA’s Office of National Marine Sanctuaries, specializing in underwater sound monitoring and management.
“As light degrades, sound travels really efficiently over really large distances, and particularly sounds that are … low tones on the piano or lower frequency,” she said. A wide range of creatures, from invertebrates to whales, use sounds to communicate with one another and pick up other cues, such as when predators or prey are close by.
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Large commercial ships, meanwhile, are the dominant human-generated contributors to low-frequency noise across ocean basins, which can interfere with animals’ ability to hear signals they need to detect. Oceangoing traffic can also add to coastal noise from smaller regional and local vessels in areas like traffic lanes approaching ports.
A ship’s propulsion system is the main culprit in emitting underwater noise, though other machinery can create vibration that can transmit noise beneath the surface, too.
Are cruise ships the main source of noise pollution?
Passenger cruise ships represent significantly less than 1% of all oceangoing vessels, according to Cruise Lines International Association, the industry’s leading trade group. However, Hatch noted that in popular cruise destinations, those ships may make up a larger portion of ships in the area.
Animals in more remote places may also be at higher risk of complications from noise pollution, but that doesn’t mean those living in urbanized environments are accustomed to it.
“Marine animals that depend on habitats where vessel noise levels are persistently high are documented to show higher stress rates, elevated predation risk and lower foraging success,” Hatch said. “These are chronic conditions that become particularly concerning if animals are already vulnerable or endangered. In areas where vessel noise levels have historically been low but traffic is increasing, such as a warming Arctic, animals have the potential for heightened disturbance as they encounter more commonly what has until now been rare noisy events.”
How are cruise ships reducing noise pollution?
Carnival Corp. and Holland America Group have developed protocols for sensitive areas, McGuire said.
Before operating in Glacier Bay, which already limits cruise ship entry to two per day, they conduct underwater sound profiling for the first vessel in each new class by sailing at different speeds, as part of a concession agreement with the National Park Service.
The process is done under the auspices of the Naval Surface Warfare Center, which sends the results to both Carnival Corp. and NPS, and ships are tested at various speeds.
When ships go at higher speeds of around 18 knots, McGuire said propeller cavitation – when vapor bubbles form and dissolve, inhibiting performance and creating noise – is the predominant audible sound source. At lower speeds, the rotation of diesel generators or motors powering functions like air conditioning show up more clearly. That information allows the operator to evaluate the noise coming from a ship and adjust plans as needed.
Holland America Group cruise lines have measured ship noise in other ways, too.
Seabourn Venture, an expedition ship optimized for sailing in polar regions, marked its first class to have its underwater noise level certified by a classification society when the vessel launched in 2022. The voluntary process provides operators with notations that a ship operates within a given sound range.
“So … because these vessels are designed to operate in sensitive areas, we’ve taken particular attention to have that noise profile measured as well,” McGuire said. Venture’s underwater sound levels came in under the relevant standard, he added.
MSC Cruises has also received “underwater radiated noise” notations for its MSC Grandiosa, MSC Virtuosa, MSC World Europa, and MSC Euribia ships, according to Linden Coppell, MSC Cruises’ vice president of sustainability & ESG.
Down the coast from Glacier Bay, Holland America Group ships also cooperate with the Enhancing Cetacean Habitat and Observation Program led by the Vancouver Fraser Port Authority, which includes several voluntary initiatives to reduce underwater noise from large commercial vessels.
In the waters around northern Washington and southern British Columbia, ships turn off their ultrasonic anti-fouling systems, McGuire said, which help prevent and unwanted organisms from attaching to a ship’s exterior, Hatch noted that ultrasonic anti-fouling systems have become increasingly prevalent on cruise ships and other kinds of vessels over the last two or three years, and are “causing some concern in the scientific community” as they emit sounds at a frequency that disturbs some toothed whale species.
“The ECHO Program is aware some ships are equipped with ultrasonic anti-fouling systems and has discussed with some operators the benefits of disabling the technology when transiting through southern resident killer whale critical habitat to further reduce underwater noise,” a spokesperson for the Vancouver Fraser Port Authority said in an email.
Other initiatives aimed at reaching sustainability goals, such as plugging into shore power in port so ships can turn off their engines, have the added benefit of reducing noise, though they may be limited in scale.
Currently, less than 2% of cruise ports worldwide have on-shore power capabilities, though that number is expected to increase to 3% by 2025, according to CLIA’s 2023 State of the Cruise Industry report. Among CLIA-member ships, more than half will be equipped to plug into shore power where available by the end of this year.
Coppell said MSC also works closely with shipyards to identify opportunities to further reduce inefficiencies, which she said are often associated with noise. “(With) every ship, there’s going to be potentially incremental improvements,” she said.
Those advances may be increasingly important.
“With a larger human population and the globalization of goods, the projectile for how much sound from vessels is in the world’s oceans is sort of ever-growing,” Hatch said.
NOAA works to highlight the circumstances that may pose risks to marine life, Hatch said.
“(Noise) has increasingly well understood physiological consequences for animals, and if they are already having a hard time making a living in the ocean, then that is that is a stressor we have to address,” she said. “We have to figure out ways to improve the quality of that habitat.”
Nathan Diller is a consumer travel reporter for USA TODAY based in Nashville. You can reach him at ndiller@usatoday.com.
