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Anti-shark tests may save baby seals
Boat-engine sounds and magnets to be used to shield pups
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By Christie Wilson
Advertiser Neighbor Island Editor

Federal marine biologists yesterday received state approval to begin testing magnets, boat engine recordings and other nonlethal deterrents to protect Hawaiian monk seal pups from sharks in the Papahanaumokuakea Marine National Monument.


That's because Galapagos sharks prowling the nearshore waters of the monument's French Frigate Shoals have foiled attempts to reduce their numbers under a controversial culling program.

"Our attempts to remove them in the manner in which we've done in the past is no longer working because the sharks have changed their behavior, and now we're forced to seek alternative ways to improve juvenile (seal) survival," said George "Bud" Antonelis of the National Marine Fisheries Service's Pacific Islands Fisheries Science Center.

A no-kill plan also is preferred by those who don't want culling taking place in the newly designated Papahanau-mokuakea preserve, which encompasses the Northwestern Hawaiian Islands.

"We set up this big preserve to protect a predator-dominant ecosystem and then immediately came in with a plan to cull the top predators. It seemed contradictory," said Dan Polhemus, head of the state Division of Aquatic Resources, part of the Department of Land and Natural Resources.

He said the situation created "an interesting balancing act" in which conservation officials had to choose whether to let nature take its course and increase the risk of extinction for Hawaiian monk seals or step in and provide protection for the more fragile of the two species.

"Nobody was entirely comfortable with this ... and as it turned out, the sharks were far too clever," Polhemus said.

Between 2000 and 2005, 12 sharks were removed from a small group of Galapagos sharks that were stalking the still-nursing pups off Trig Island in French Frigate Shoals, a 22-mile-long complex of reefs and sandbars 560 miles northwest of Honolulu.

The cull substantially reduced pup deaths from predation, according to Antonelis. Only eight such fatalities occurred in each of the last two years at the shoals, he said.

By comparison, there were 31 known fatal shark attacks on monk seal pups in 1997, the worst year on record.

But in 2006 and 2007, no sharks were taken because they had become wary of human activity and kept their distance, Antonelis said.

"What we'd done unintentionally is taught the sharks to avoid us, with this heightened sensitivity to our presence. We're hoping to use that avoidance behavior as a mechanism by which we can deter them from the pupping areas."

Messing with mealtime: A panel of shark and seal experts convened in January to discuss nonlethal shark deterrents to be tested in field trials starting next month.

Since the sharks at French Frigate Shoals have shown aversion to humans, one idea is to moor an 18- to 20-foot boat in the waters off Trig Island to give the impression that humans are present.

Another idea is to use amplified noise to mimic the sound of an approaching boat.

Scientists also want to test whether magnetic and electric fields can repel sharks from specific hot spots.

A fifth proposed deterrent would attempt to ward off sharks using visual arrays made of PVC tubing, fishing floats or foam "noodles." The devices would be installed in a way that wouldn't present an entanglement hazard, and could be used alone or in combination with magnetic arrays.

"There has never been an experiment like this in the past. Our ultimate goal is to reduce the number of pups being preyed upon," Antonelis said.

The seal population, estimated at 1,100 to 1,200, is at its lowest in recorded history. Since 2000, the population has been declining at a rate of 4 percent annually, according to Antonelis.

The primary reason is the low rate of juvenile survival. "Because we have fewer young animals growing up to join the ranks of the reproductive population, as those older animals die out from natural causes, the overall population level declines and fewer and fewer pups are born," he said.

In 2007, only 151 pups were born throughout the entire Northwestern Hawaiian Islands.

Many of the pups have been dying from starvation, thought to be due to competition for food with ulua and other top predators, Antonelis said.

Marine debris, which can entangle seals, and sharks are other causes of monk seal deaths.

Quirk of behavior: Marine biologists have been successful in relocating weaned pups to areas where sharks are not as great a threat, Antonelis said. Helping the youngest seals has been more challenging, and predation by Galapagos sharks at French Frigate Shoals is a new development.

"Through a series of unusual ecological events, it is suspected that the sharks learned to prey on pre-weaned pups. There is no other place in the Hawaiian archipelago where a small group of sharks have learned this behavior," he said.

Evidence indicates that only about 20 Galapagos sharks, which grow to 10 to 12 feet in length, were hunting monk seal pups at Trig Island, where the problem was first detected. As their numbers were culled, no new sharks joined the group, indicating the behavior was limited to that single population of sharks.

Why the sharks came to Trig Island in the first place is not clear. Antonelis said scientists think that when Whale-Skate Island, another low-lying islet within French Frigate Shoals, was lost to erosion, monk seal moms and their pups were driven to Trig, creating a greater concentration of animals — and more meal opportunities for sharks.

In addition, attempts by two aggressive male seals to mate with weaned pups at Trig suffocated or drowned a number of the younger animals. Antonelis said their carcasses in the water attracted Galapagos sharks that soon discovered more good eating.

"We relocated the males to Johnson Atoll but we weren't able to deal with the fact the sharks developed a behavior that focused on predation on pre-weaned pups," he said.

The Board of Land and Natural Resources yesterday granted a permit for the shark-deterrent experiments, which are planned for early May through September, during the pupping season.

Polhemus of the Division of Aquatic Resources said there could be useful implications from the research for similar conservation work in the main Hawaiian Islands, but that it is unlikely the state would consider the same shark-deterrent techniques to protect humans.

One reason is that the deterrents proposed for French Frigate Shoals have limited range and are meant for targeted use at specific sites, not the vast offshore expanses popular with people.

Another is that there are few shark attacks in Hawai'i on humans — an average of three to five annually.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.

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