Southern migration of seals a concern

By Jan TenBruggencate
Advertiser Science Writer

The number of Hawaiian monk seals in the main Hawaiian islands is growing, even as the larger population in the Northwestern Hawaiian Islands falls, and researchers want to know why.

They also want to know whether seals exposed to land mammals and their diseases in the main chain, from the Big Island to Kaua'i, could endanger the fragile populations in the outlying islands from Nihoa Island to Kure Atoll.

"The big concern is: What is the health of these seals, what are the health hazards and do they pose a threat to the seals in the Northwestern Hawaiian Islands," said Bud Antonelis, chief of the protected species division in the National Oceanographic and Atmospheric Administration's Pacific Islands Fisheries Science Center.

The agency awarded a grant to marine mammal veterinarian Robert Braun to oversee a project to study the animals. He will conduct tests on seals to assess their physical condition and will attach satellite transmitters to track their movements in Hawaiian waters.

"Monk seals involved in this work will be tested for exposure to ... bacteria, viruses and parasites from wildlife, livestock, feral animals and pets as well as humans," Braun said.

Researchers also are concerned about the relationship between people and seals on popular beaches. Last week a 2-year-old, 300-pound seal was moved from Kona's Kealakelua Bay for a second time because it was grappling with swimmers and nipping them. On Kaua'i, federal wildlife officials warned residents not to feed a monk seal that appears to have grown accustomed to handouts at Nawiliwili and Port Allen.

Hawaiian monk seals are one of only three species of tropical seals. While the survival of the Hawaiian species has been a longtime concern, those seals are healthiest of the lot. The Caribbean monk seal species is believed to be extinct since the late 1950s; Mediterranean monk seals number about 500.

At first glance, the population of monk seals in the main Hawaiian islands, though small, appears to be remarkably healthy.

There are about 1,250 Hawaiian monk seals in the Northwestern Hawaiian Islands, and at least 50 in the main islands. While the population in the isolated atolls, reefs and islands to the northwest has declined by about 60 percent since the 1950s, the numbers in the main islands are growing.

Only a decade or two ago, seals were rare sights in the main islands. Now, there have been births on each of the eight main islands, including Kaho'olawe. The biggest population seems to be around Ni'ihau.

"The ecosystem here is so different, but the animals here seem to be thriving," said Jeff Polovina, acting director of NOAA's Pacific Islands Fisheries Science Center.

One recent finding from biological surveys is that the percentage of predators that feed near the surface of the ocean and compete with the seals — notably sharks and jacks — is much higher in the Northwestern Hawaiian Islands.

The result may be that seals in the main islands face less competition for food.

The environment in the Northwestern Hawaiian Islands is different. Reefs there, which are larger and in a more natural state, appear to have a greater quantity of biological resources. There is less human interaction and less sedimentation of the habitat.

One question, Polovina said, is whether the seals in the main islands are using the coastal resources differently than their cousins up north.

There are no clear estimates of the population of Hawaiian monk seals before humans arrived. They were killed by early sailors for food, for their pelts and for oil. The population dropped steadily through the past half-century, until it stabilized in the past decade.

"The best we've been able to do is stabilize the decline," Antonelis said.

Scientists have identified a series of threats to the Northwestern Hawaiian Islands seal population. A shortage of food appears to reduce pup size and their ability to survive in certain years. Shark attacks also cull the population, and seals have been killed when they become entangled in nets and ropes.

Monk seal behavior in itself is another problem: Aggressive males can injure or kill females and pups, a trait seen in other seal and sea lion species.

Antonelis said researchers are conducting several programs to protect the seals. One, at French Frigate Shoals, is to move newly weaned pups whose mothers are no longer protecting them to areas where sharks are less common.

Teams of researchers spend each pupping season on six islands: French Frigate Shoals, Laysan, Lisianski, Pearl and Hermes Atoll, Midway and Kure Atoll. They conduct population studies by identifying individual seals by their scar patterns and other unique features, then documenting the life of the seal. The researchers also remove debris that could entangle seals and they disentangle seals when necessary.

State wildlife manager Dave Smith said his teams regularly find entangled seals when they visit the state refuge at Kure Atoll.

"On numerous occasions we've found seals entangled in nets or with packaging straps cutting into their flesh. There are a lot of ghost nets (lost nets that kill wildlife) out there that we never see. We don't know how big that impact might be," Smith said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.