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A black rope had rubbed the whale’s flesh raw and white, making it easier for marine mammal rescuers to see the months-old humpback entangled in fishing gear off Cape Cod, Massachusetts. Using a nine-meter pole tipped with a sharp hook, rescuers from the Center for Coastal Studies (CCS) cut away the tangled gear—one of several similar rescue operations the team conducts each year.
The vast majority of the team’s rescue attempts are a success. But to Bob Lynch, CCS’s rescue operations manager, their efforts are a band-aid fix. There are many whales they can’t get to, he says. Beyond that, while disentanglement can save a whale, it can’t save the species, says Lynch. “What we’re doing is not a solution to the problem whatsoever.” Preventing whales from getting entangled in the first place will have a larger impact on their protection.
Vessel strikes and entanglement in fishing gear are the leading causes of human-caused mortality for humpbacks and other baleen whales. Over the past several years, scientists and conservation managers around the world have tried all sorts of things to prevent entanglements, including testing ropeless gear, increasing marine litter cleanup efforts, and implementing seasonal closures of areas that whales frequent. But off the Massachusetts coast, research led by Tammy Silva, a marine ecologist at the Stellwagen Bank National Marine Sanctuary (SBNMS), hints at another way to find whales and hopefully prevent their entanglement. Key to the approach is the overlap of habitat use between humpback whales and one kind of seabird—the brown-washed great shearwater.
North of Cape Cod Bay, in the choppy waters off the SBNMS, great shearwaters often gather in the hundreds. Through tracking studies, Silva and her colleagues have shown that a congregation of great shearwaters can signal that a pod of humpback whales is swimming below. Both species are preparing for an offshore feast—the whales ascend from the deep to capture sand lance, a silver eel-like fish. Shearwaters lie in wait to pick from what the whales miss.
While it’s possible to track whales directly using satellite tags, the approach can be expensive, and the tags have a short life span. Catching and tagging seabirds, says Dave Wiley, SBNMS’s research coordinator, is also much easier than tagging a humpback whale.
Tracking shearwaters starts with getting birds in hand, Silva explains. Because great shearwaters spend the bulk of their lives on the open ocean, traveling to land only to breed, researchers have to capture them at sea. So, each year since 2012, the team has choreographed what Silva describes as an alien abduction.
Launching in a small inflatable boat from their mother ship, a 15-meter vessel in the Gulf of Maine, three or four team members set out after a raft of shearwaters. One team member tosses chopped mackerel and squid to lure birds in, while the others use long handheld nets to scoop the birds into the boat. Working quickly to minimize stress on the animals, they place each bird in a cat carrier to relax.
After they’ve caught several birds, they head back to the mother ship. There, the scientists collect samples to gauge each bird’s health and diet, and stitch a small solar-powered satellite tag to the skin between its wings.
Tagging and tracking 58 birds over five years has revealed the significant overlap between where and when great shearwaters and humpback whales meet en masse. Now, Silva and her colleagues hope to use this data to save humpbacks from life-threatening entanglements.
Identifying overlaps in known persistent hotspots, like SBNMS, means that now they can look farther offshore. “Take Georges Bank,” says Wiley, “no one’s going to Georges Bank to look for humpback whales.” But if enough shearwaters show up in the area between Cape Cod and Nova Scotia during a particular time frame, there’s a good chance that humpbacks are in the area, too.
There’s still a lot of work left in developing their real-time bird-based system for predicting the presence of humpback whales. But the team hopes that, in the future, detecting an aggregation of tagged birds could trigger action from marine management teams. Fishermen could be required to move gear, and boaters could be asked to steer clear of the area.
It’s a lot like how a phone or smartwatch can track its owner’s location through a constant update of information. “It’s really an extension of our everyday lives,” says Silva, “taking in real-time data and applying that to conservation.”
Maintaining the long-term data collection from shearwaters is central to both Wiley and Silva’s hopes for the future of the project—as highly mobile species, seabirds are a top indicator of ocean patterns and can help answer key questions about the health of marine life, including whales. To protect humpbacks, we have to change our approach, Silva says. “Ultimately, coexistence is what we’re after.”