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The left-handed hermit crab, one of the many creatures living in Hawai'i's intertidal zone
Vol. 11, No. 6
December 2008/January 2009

  >>   Teaching Aloha
  >>   Inside Fortress O'ahu
  >>   What Lies Beneath

Home Again 

story by Christopher Pala

On a recent Sunday, I was surprised to see a strange object moving toward the shore at Queen’s beach on the eastern end of Waikïkï. It was the pointy head of a Hawaiian monk seal, a creature that was once so rare in the main Hawaiian Islands that the first recorded sighting dates from 1928.

There were a dozen people in the water between the seal and the beach, so it turned, swam around a jetty and landed on an even more crowded beach. About fifty people gathered as the glistening black animal—7 feet long and weighing 500 pounds, I would later learn—hauled out on the beach, its blubber rolling in waves across its body as it climbed the slope (unlike sea lions,seals don’t use their fins to walk on land; they move like caterpillars). Its dark, soulful eyes surveyed a solid wall of camera-wielding spectators not 20 feet away. The crowd ignored a man urging them to step back and give the seal space. When another man got within 6 feet of the seal’s head for a closeup, it rolled languorously back into thewater and swam away.

A scene like that would have made headlines only fifteen years ago, but today, following a remarkable change in the seals’ behavior, it has become commonplace, to the delight of biologists and tourists alike.

Few animals are as studied as the Hawaiian monk seal, which became the official state mammal this year (not to be confused with the official state marine mammal, the humpback whale). More than 500 volunteers around the Islands and some two dozen state and federal officials are involved in counting, observing, protecting and, when they die, performing autopsies on them. There are tissue samples for nearly every individual seal that has lived in the last ten years. DNA from those samples tells scientists which seal is related to which, and how.

And yet the monk seal remains one of the animal kingdom’s biggest puzzles.

Typically, marine mammals thrive in pristine environments. The Northwestern Hawaiian Islands (NWHI) have been mostly undisturbed since the late 1950s, when the first count was made. Yet the monk seal population there has been dropping at an average rate of 4 percent since then. In the midst of abundance—the estimated weight of all fish in the NWHI averages 2,000 pounds per acre—the females are thin. They are unable to provide enough milk to their pups; the pups have too little fat to sustain them while they learn to find food and avoid predators. Most starve or are eaten by sharks.

Conversely, marine mammals usually fare poorly in environments like the main Hawaiian Islands, where their food—fish, octopus and lobster in the seal’s case—is growing scarce. Today, after decades of overfishing, the average fish concentration in the main Hawaiian Islands is 600 pounds of fish per acre, less than a third what it is in the NWHI. Yet the monk seals have prospered here, growing from single digits to more than 100 in a decade. The females observed in the main islands are fat and sleek, and when the pups wean, they too are bursting with health— even near overcrowded, overfished O‘ahu, where the average density is 250 pounds of fish per acre. These days, a dozen pups are born every year, and nearly all survive: an average yearly increase of 8 percent. The animals here are “absolutely massive” compared with those in the NWHI, says Charles Littnan, chief scientist for monk seals at NOAA, the National Oceanic and Atmospheric Administration.

Scientists are not just surprised; for now, they’re stumped.