It’s summer on Stellwagen Bank, 50 miles north of Chatham, Massachusetts, on the Gulf of Maine in the Atlantic Ocean. When the sun rises on this day in late June, the bank is home to seabirds, many of them large shearwaters, and humpback, fin, and minke whales. For all of these species, the season depends on a feast of tiny fish called sand spears, abundant in the region at this time of year.
The shearwaters circle over the 50-foot research vessel Auk. Next door, the fins and tails of humpbacks break the ocean’s surface. On board the ship, researchers can enjoy a simultaneous aerial and underwater ballet in the front row. As they marvel at the spectacle, they are also working to keep an eye on all the players, from huge whales to small fish, to track the health of their ecosystem at a time of unprecedented ocean warming.
Greater shearwaters spend most of their lives at sea, riding white-crested waves on long, stiff wings or feeding in groups of small fish, often with other seabirds and whales such as humpbacks.
“Shearwaters are named for their gliding flight, which climbs these thin-winged seabirds just above the tops of the waves,” writes Nathalie Ward in Stellwagen Bank: A Guide to the Whales, Sea Birds, and Marine Life of the Stellwagen Bank National Marine Sanctuary . “Leaning from side to side to adjust the sail, the birds effortlessly navigate updrafts between the waves, occasionally skimming the trough of the wave, only to reappear beyond the next crest.”
As the shearwaters move from swell to swell, a young humpback spins up and out of the sea, pirouetting its full length and spraying sparkling water droplets in all compass directions before slipping beneath the waves.
In 1992, Stellwagen Bank became New England’s first and only national marine sanctuary, a wild ocean spot not far from the urban world of Boston. It was historically important as a fishing ground. Today, it is an oasis for marine life, from the microscopic to the giant.
A decade later, in 2002, Stellwagen was designated an Important Bird Area (IBA). The IBA program, administered in Massachusetts by Mass Audubon, is part of BirdLife International’s work to conserve bird habitat. An IBA provides essential habitat for breeding, wintering, and/or migratory birds and supports high-priority species, significant bird aggregations, and exceptional bird habitat or has high educational or research value. Stellwagen Bank meets all of these criteria, says marine biologist David Wiley, research coordinator for the Stellwagen Bank National Marine Sanctuary.
The great shearwater is one of the few bird species that breeds in the southern hemisphere, migrating north to its non-breeding range in the northern hemisphere. From November to April, the seabird is found along the Patagonian shelf off Argentina and in large nesting colonies on some rocky islands in the South Atlantic, including Tristan da Cunha. Then, in May, the shearwaters head north along the coasts of South and North America. From June to November, they can be found in the Caribbean and on the eastern coasts of the US, Canada and Greenland before crossing the ocean and flying south along the western coasts of Europe and Africa towards their islands. Of reproduction.
Shearwaters use Stellwagen and the Gulf of Maine as feeding grounds mainly from July to November, although the first birds arrive in June and some remain until December. The species is also reported in reduced numbers from January to April along the coasts of Alabama, Florida, the Carolinas, Virginia, and the Bahamas, suggesting that at least some individuals do not fly as far as the South Atlantic each year.
More than 40 species of seabirds summer on Stellwagen Bank; In addition to Greater Shearwaters, the shoal attracts Sooty and Manx Shearwaters, and Wilson’s and Leach’s Storm Petrels.
“Seabirds are excellent indicators of the health of the marine ecosystem,” says Wiley. “They allow us to track changes in the environment over time, from their summer feeding area on Stellwagen to their migratory routes and breeding grounds.”
Humpback whales also migrate long distances, up to 10,000 miles each year. The whales feed in summer in northern waters such as Stellwagen, then migrate to tropical or subtropical waters to breed and give birth in winter, when they live on blubber stores.
capture of sea birds
What sustains the bank’s summer visitors: birds and cetaceans? To find out, scientists are tracking both shearwaters and whales. As it turns out, the answer lies in countless small silver sand spears.
Since 2013, Stellwagen scientists and their colleagues have attached tags to great shearwaters. To catch their prey, the researchers recruit crew members aboard the Auk , which serves as the mother ship for two smaller vessels, the rigid-hulled inflatable boats (RHIBs) Balena and Luna .
Biologists use the Moon to navigate to where shearwaters feed ( Balena is for whale research). Then they attract the birds with cut fish and squid. Once a shearwater approaches the boat, it is captured with a long-handled net and finally attached to a satellite tag (Platform Terminal Transmitter or PTT) powered by solar or battery power and released. Birds are normally tagged during research cruises in June, July and/or September.
Why study the great shearwater instead of another of the many species of seabirds that frequent Stellwagen in summer? As Wiley, Kevin Powers, a marine sanctuary biologist, and their colleagues wrote in 2017 in the journal Marine Ecology Progress Series : “In the western North Atlantic, great shearwaters are among the most abundant seabirds during the summer months, but little is known about them. their ecology of movement and habitat requirements in this ecosystem”.
The data from the PTT tags allow researchers to monitor the movements of the shearwaters. Scientists can compare birds’ flight paths with water temperatures, chlorophyll concentrations, ocean shorelines, and other factors that might affect bird prey. While the analyzes are primarily focused on understanding the shearwaters’ food source, the tags have also allowed biologists to track the birds as they migrate south.
In celebration of Black Birders Week 2021, for example, that year’s class of tagged great shearwaters included a bird named Shuri after a character from the Black Panther movies. DNA from blood drawn when the bird was tagged showed it to be a female.
From the day she was tagged, July 14, 2021, to January 1, 2022, when her tag failed, Shuri traveled 26,465 miles from Massachusetts coastal waters to the south-central South Atlantic. He was the distance leader in the 2021 shearwater class.
tagging whales
Shearwaters are just one part of the Stellwagen Bank landscape. Then there are the whales.
If attaching a tracking tag to a shearwater is no easy feat, doing the same to a humpback whale is much more challenging. On a bright morning after the summer solstice, the Balena transports biologists to the center of a pod of whales. There, in an attempt to attach a tag to a humpback whale, the researchers hope to get close to a whale whose flank, where the tag will be attached, is exposed.
Scientists are using a suction cup tag, called CATS, for personalized animal tracking solutions. CATS tags carry two video cameras, along with accelerometers, gyroscopes, and sensors to monitor temperature, light, and other variables. The instruments observe the mechanics of the whale’s feeding, as well as “seeing” other humpbacks in the same area as the tagged whale.
Wiley takes the helm of the Balena ; the Luna is the chase ship that follows, ready to see where a whale goes immediately after being tagged. Suddenly, a humpback surfaces near the starboard side of the Balena . The crew is fully operational. Wiley guides the boat alongside the whale, while team member Mike Thompson, a Stellwagen researcher, extends a 40-foot-long pole toward the whale. At its end it has a CATS label mounted. Hopefully Thompson will gently place the tag on the humpback. “Tag on!” He screams as the whale disappears under the waves.
“Look at this place,” Wiley says, turning halfway from the Balena ‘s helm to see a group of humpbacks with shearwaters flying overhead. “Seabirds and whales, everywhere.”
‘It all depends on the sand lance’
Stellwagen Bank, with its sandy bottom and relatively shallow water, is prime habitat for sand lances that support birds and whales. Traveling in huge shoals numbering in the tens of thousands, sand spears from the shoal provide seabirds and whales with high-calorie meals.
At night, the sand tunnels into sandy sediments or forms shoals near the seafloor. During the day, the fish usually swim in dense mats along the seafloor. Where sandspears are found in the Gulf of Maine, shearwaters and humpbacks are also found. “Shearwaters and other seabirds, whales and just about anything that forages here feeds on these fish,” Wiley says. “At the Stellwagen Bank everything depends on the sand lance.”
Large shearwaters and humpback whales head toward areas where sandspears are plentiful, according to data Wiley and others published in October 2020 in the journal Conservation Science and Practice . “The strong coexistence between these predators and their sandspear prey suggests that it is important to identify where sandspears live,” says Wiley. “Discovering more information about sand lance habitats may indicate other areas where shearwaters and whales aggregate.”
More than 70 species depend on these tiny fish, reports Michelle Staudinger of the Northeast Climate Adaptation Science Center at the University of Massachusetts Amherst. She and her colleagues, including Wiley, published a 2020 report in the journal Fish and Fisheries that further documents the dependency of countless species, from great shearwaters to roseate terns, Atlantic puffins, humpback whales, bluefin tuna and Atlantic cod, of the sand lance.
To see where the fish are hiding, Wiley and the crew use a seafloor observing system known as SEABOSS, or SEABed Observation and Sampling System. According to Thompson, this square eye in the sea allows researchers to collect sediment samples and get videos of places frequented by sandblasters on the seafloor. Sand lance surveys are conducted at 44 stations on or near Stellwagen Bank at various times of the year, including about a month prior to the research cruise each June.
water heating
If trends continue, shearwaters and humpbacks may soon be in need of fish finders. Fish communities on Stellwagen Bank have changed dramatically, according to marine scientists Peter Auster of the Mystic Aquarium and Christian Conroy of the University of New Haven. A 2019 report they co-authored on the Stellwagen Bank fishes details species changes that began in the early 1980s.
Those years marked the beginning of a two-decade period of steadily rising sea surface temperatures. The waters of the northeastern United States continental shelf have warmed at three times the global average rate. In response, many species in the Gulf of Maine moved to greater and cooler depths. However, for some species, such as the sandspear, the deeper realms may not offer suitable habitat. Sand spear is based on sand or fine gravel, sediment that makes up most of the bottom in the shallows of Stellwagen Bank, but is not as common in its depths.
“The relatively minimal number of sand spears collected in trawl surveys conducted since 2010 may reflect, in part, the results of this compression between warm water and preferred habitat,” Auster and Conroy say.
In fact, the sand lances seem to change locations every year, taking seabirds and whales with them.
Although the June research cruise was scheduled to depart Provincetown, the sandspear (and seabirds and whales) took up residence off another Cape Cod port, Chatham. To keep up with the changing scene, the scientists moved the Auk from its berth in Provincetown to a dock in Chatham. “We may care about the birds and the whales,” says Wiley, “but they care about the sandblasters. So, we look at where the sand lances are concentrated.”
feeding frenzy
To catch sand spears in Stellwagen, humpback whales use bubble nets, a means of feeding on small fish. One or more whales blow or submerge and then exhale together underwater. When its bubbles reach the surface, they form a large ring with sea foam in the center. The bubble ring turns into a net that catches countless sand spears. Seconds later, a whale (and then several) emerges in the center of the ring, its huge baleen mouths open, filtering the water or trailing, as marine biologists call it, a spear of sand.
Humpbacks release the bubbles as they swim in upward spirals, often during a behavior called double loops. “Double loops” begin with an upward spiral to corral fish, then the strike of a fin fin on the ocean surface, and a second lunge to capture cornered prey. Whales work in teams of two to ten or more, rising to the ocean’s surface in a boiling cauldron of gaping mouths and tumbling fish.
Waiting just above are great shearwaters and other seabirds, who take the liberty of walking on top of the whales as they break the surface, brazenly snatching spears of sand from the leviathans’ mouths.
Will the sand-spear buffet be enough to keep the seabirds and whales alive until they return the following summer? At Stellwagen Bank, the fate of shearwaters, humpbacks and many other seabirds and cetaceans is intertwined with that of a very small fish.