Study documents acoustic footprint of human activities in the Cook Inlet waters, finds sound levels often exceed harassment limits set by NOAA.

By Ben Boettger, Earth Island Journal

Light penetrates just a few feet into the slate-gray water of Alaska’s Cook Inlet. Further down, suspended glacial silt creates a cold, opaque space where vision is little help to a foraging predator. To nab halibut and flounder from the muddy bottom, to chase salmon through shallows and river mouths, one needs to rely on other senses.

Cook Inlet’s belugas have inhabited their small world — a shallow, 230-mile long gash in Alaska’s mountainous south-central coast — for thousands of years, isolated geographically and genetically from other Alaskan belugas. Hunting by echolocation and using signature calls to find and identify one another, sound has let them prosper in their dark environment.

Manuel Castellote, JISAO

Humans have been eavesdropping on the belugas’ sonic world. Between 2008 and 2013, the Cook Inlet Beluga Acoustics team — which is composed of federal, state, and university scientists — created the most complete hydrophone recording of their habitat to date. Their primary goal was to learn more about where belugas forage, but with the same dataset they also listened for the noise of another species: their own.

The resulting study, published in late 2018, looked at 14 months of recordings (spanning all of a year, though not continuously) from seven locations with heavy overlap between beluga and human activity. It found human-caused (anthropogenic) sound in every recorded day — from ship traffic, jet and propeller aircraft, oil and gas extraction, dredging, pile driving, and motor boats, much of it potentially able to drown out beluga echolocation and signature calls. Sound levels often topped the harassment limits that the National Oceanic and Atmospheric Administration created to protect the endangered belugas — but in a way that escapes NOAA’s controls on harassment.

Cook Inlet’s industrialization over the past several decades has created this matrix of anthropogenic noise. In 1979, the first population estimate of Cook Inlet belugas put their number at 1,293. Their habitat that year was in the midst of economic transformation. Alaska’s first oil had been discovered twenty years before, just east of Cook Inlet. Through the ’60s, exploratory drilling and seismic surveys — which use the echoes of underwater airgun blasts to map below the seafloor — discovered three oilfields in the inlet itself. By 1979, the Cook Inlet belugas shared their environment with 14 oil and gas platforms served by a network of underwater pipelines. Between 1960 and 1980, Cook Inlet’s shoreline city of Anchorage almost tripled its population, while some smaller towns in the area doubled theirs. By 1995, about 60 percent of Alaskans would live in the Cook Inlet watershed. Between that year and 1998, Cook Inlet’s belugas would decline by 47 percent.

Around this time, beluga researchers reached two conclusions. First, unregulated hunting was sending the Cook Inlet beluga population toward extinction. Second, genetic analysis showed that other belugas may have separated from their Cook Inlet brethren around the end of the last Ice Age, and would probably not repopulate the area any time soon. The disappearance of belugas from Cook Inlet was likely, and would likely be permanent.

Responding to these findings, Alaska Native groups voluntarily restricted their beluga hunts in 1999 and ended them in 2005. (By then, hunting was restricted to subsistence and culturally based hunts by Native Americans, who were exempted from the bans imposed by 1972’s Marine Mammal Protection Act). A sustainable hunt could resume when the population rebounded — a matter of time, scientists and hunters assumed, if everyone stopped taking belugas from the breeding pool.

In fact, ending the hunts slowed but didn’t stop the trend. The beluga population has continued declining by about 1.3 percent every year since. NOAA presently estimates there are fewer than 350 Cook Inlet belugas. When the agency listed the whales as endangered in 2008, the conservation focus shifted from hunting to habitat integrity. In 2011, NOAA protected 3,016 acres of Cook Inlet water as critical habitat — yet the population trend remains fixed. The Cook Inlet Beluga Acoustics team is now one of several trying to decipher the tangles of cause and effect still preventing the belugas from rebounding.

In spite of Alaska’s unspoiled “Last Frontier” image, Cook Inlet is an urban and industrial body of water. Its oilfields are responsible for heating, fueling, and powering most of south central Alaska. Anchorage, the state’s largest population center with 294,000 people, sits on its shore. To its north is Elmendorf Air Force Base, where fighter and transport jets regularly take off over the water on training flights. Anchorage International Airport, among the busiest air cargo hubs in the world, also has a flight path over the water. About half the food, products, and other cargo entering Alaska travel up Cook Inlet to land in Anchorage at the Port of Alaska. The fine silt that pours through Cook Inlet from its glacier-fed source rivers fills up this essential harbor so quickly that the Army Corps of Engineers has had to dredge it out every summer since 1958, scooping out up to 1.8 million cubic yards of silt and dumping it in the middle of the nearby strait. All of this is noisy.

When a car drives down your street with rattling suspension, thumping stereo, and no muffler, you and your neighbors might feel harassed by noise. In the Cook Inlet, the aquatic equivalents of this loud car are the dredging, pile-driving, and seismic exploration for offshore oil and gas reservoirs. Those companies and government entities making the noise get permission to work in Cook Inlet from NOAA by filing for Incidental Harassment Authorizations. These authorizations allow them to make more than 125 decibels of noise — the level at which NOAA defines noise as harassment of marine mammals — if the agency determines it would not affect too many whales. The permits sometimes require trained observers to watch for whales near the work site, halting the job if any are spotted. Anchorage’s harbor dredging, for instance, stops if belugas are seen within 50 meters.

The effectiveness of the permitting system is debatable — in one month of recording at one location in the inlet, hydrophones picked up two instances of unpermitted noise harassment, and the new paper recommends better enforcement of harassment rules. But even when rules are perfectly enforced, the existing system still lets noise “exceed behavioral harassment levels on a daily basis in a significant portion of the critical habitat,” the acoustic researchers wrote. Incidental Harassment Permits aim to keep too many loud cars from cruising too often through the belugas’ neighborhood. But if individually quieter cars pass through, there are no rules to control them collectively — even if they reach highway traffic density and together are as loud or louder than the mufferless rattletrap.