Blasts spark research project
Scientists worry devices used by fishermen are harming marine mammals
With an underwater gorge deeper than the Grand Canyon, the Monterey Bay National Marine Sanctuary is often called the “Serengeti of the Sea” — a place teeming with diverse, unique and legally protected aquatic wildlife.
It’s not the kind of place where you would expect to hear bombs going off. But for decades, Monterey Bay fishermen have been using small explosives called “seal bombs” to chase away voracious sea lions who have figured out where to get an easy meal. And the practice is increasingly raising concerns among scientists and environmentalists, setting up a possible confrontation with fishermen, many of whom say that without the devices their livelihoods would be seriously threatened.
“My biggest worry here is that the seal bombs are doing tremendous acoustic damage to whales, dolphins” and other marine mammals, said Jason Scorse, an ocean policy expert at the Middlebury Institute of International Studies in Monterey. “If you’re throwing thousands of bombs in the water in an international marine sanctuary, my worry is that this is doing long-term damage that we’re just letting go on year after year.”
Seal bombs, which some fishermen prefer to call “seal controls,” are meant to be thrown near sea lions to frighten, not injure, the animals. Roughly the size of an index finger, the firecrackerlike
devices emit a bright flash when lit. Above water, the bang is about 160 decibels, slightly louder than a shotgun blast. But because sound waves travel faster and farther in water than air, the
seal bomb explosions can be heard throughout the sanctuary.
“It is a powerful concussion that’s similar to what police use as a flash bomb or a con
cussive bomb,” said Philip Sammet, a professional diver and dive boat captain who moved to Monterey in the late ’80s. “It just stuns you.”
The National Oceanic and Atmospheric Administration has developed guidelines for how and when fishermen should use seal bombs — never, for example, when dolphins or whales are visible. But the guidelines were developed decades ago, before the robust return of humpback whales and other endangered marine mammals to Monterey Bay.
Originally, seal bombs were intended to chase sea lions out of fishing nets. But Monterey Bay fishermen say they now mainly use them to steer squid, anchovies and other fish into their nets. This is particularly helpful when sea lions are swimming through and dispersing schools of fish that fishermen are trying to net.
Before the landmark Marine Mammal Protection Act of 1972 made it illegal to “harass, hunt, capture, or kill” marine mammals, fishermen used harsher methods than seal bombs to deal with the pesty pinnipeds.
“I’m gonna be frank with you,” said 79-year-old Neil Guglielmo, who has been fishing out of Monterey since 1956. “Years ago, when they weren’t protected — and there were very few compared to today — we used to shoot at them to scare them away. They were in fear of the rifle. The smell of the gun and stuff like that — they would go away.”
After the 1972 law was signed by President Richard Nixon, the West Coast sea lion population rebounded from about 30,000 a halfcentury ago to an estimated 300,000 today. The population explosion has created an army of hungry competitors for fishermen, many of whom believe that seal bombs are now their only viable option to fend off sea lions if they want to stay in business.
Anne Simonis, an Oakland-based acoustic ecologist and oceanographer for the National Marine Fisheries Service, said scientists “honestly don’t know” if the noise from seal bombs is “a problem or not.” That, she said, is why researchers want to find out if the blasts are seriously impacting the sensitive ecosystems of the Monterey Bay. And if that’s the case, Simonis said, the goal of scientists will be to work with policymakers and fishermen to revamp NOAA’s outdated guidelines.
To figure this out, Simonis and other researchers are looking into the relationship between seal bombs and harbor porpoises, which have the most sensitive hearing of any mammal in the Monterey Bay.
Research shows that harbor
porpoises change their behavior to avoid various types of noise. One 2018 study by Danish researchers found that any sound 96 decibels or louder was enough to chase the mammals from their feeding grounds.
So far, the team of researchers — which includes scientists from NOAA, the Naval Postgraduate School in Monterey and the Monterey Bay Aquarium Research Institute — has collected six months of recordings at five sites throughout the Monterey Bay to better understand the region’s underwater noise. They then created a model to estimate how far the sound from a seal bomb would carry, concluding that the noise can be heard throughout the 6,094 square miles of the Monterey Bay sanctuary.
“What sounds like a muffled poof from the deck of the ship is actually a piercing, high-intensity noise that travels more than 10 miles underwater,” said John Ryan, who manages a MBARI project that placed an underwater microphone on the seafloor to listen to the sounds of the Monterey Bay in 2015.
Ryan said when he saw that the sound from a single small explosive device carried over 15 miles underwater from Davenport to Monterey Canyon — “even bending over the edge of the
continental shelf and going down into the bottom of the canyon — that tells us how well sound travels in water. Just that fact alone is almost the entire foundation for understanding why we care about this.”
The studies are part of a growing recognition worldwide that loud underwater noises can impact sea life — especially marine mammals that rely on sound for navigating as well as finding food.
An international study published in the February edition of the journal Science looked at more than 10,000 studies on the impact of ocean noise pollution on marine life. The research found that animals in noisier patches of the ocean were more prone to starvation and hearing loss.
Scientists have shown that the background noise intensity off the coast of California since the mid-1960s has increased 16-fold.
Fishermen say they understand the researchers’ concerns, but many feel that their attention is disproportionately directed toward the seal bombs, as opposed to the noise caused by the huge increase in cargo ship traffic in recent decades.
Many fishermen also argue that the overriding problem isn’t the noise from seal bombs — it’s the overabundance
of sea lions crowding West Coast waters.
Guglielmo said there are times when as many as 20 sea lions will swarm into a purse seine net, which looks like a giant drawstring bag. That, he said, can scatter the fish or even damage his gear.
“Without the seal controls, I probably wouldn’t be getting anything,” Guglielmo said.
Some fishermen, however, question the effectiveness of seal bombs, arguing that they only momentarily startle sea lions before they’re back on the attack.
“In my opinion, they’re more of a dinner bell than anything,” said Jerid Rold, a fourth-generation fisherman in Moss Landing. “I would never throw one, just because as soon as you throw one there’s a million seals that just come to it. It’s like ‘Hello, there’s food over here!’”
Scientists say they sympathize with the fishermen’s plight and hope that their emerging research will lead to better strategies to help fishermen cope with their longtime nemeses.
“Our job is always to improve our understanding of the interactions between human activities and the natural environment and its inhabitants,” Ryan said. “And we always have more room to understand that better.”