In penguinlike tuxedoed masses, the Tyuleni Island murres were standing in murmuring hordes, crowding the rock ledges of their remote breeding colony off the east coast of Sakhalin in the Sea of Okhotsk.

Their extinct, giant relative, the great auk (Pinguinus impennis), was the original penguin, the Northern Hemisphere species whose scientific name was appropriated and used for an unrelated group of Southern Hemisphere birds. Now, the only surviving link to the great auk are the two species of murres -- thick-billed and thin-billed -- which in winter may be spotted in Japan, where they are unflatteringly called umigarasu (sea crows).

Feeding and drinking from their ocean homes, murres remain at sea for most of each year but must visit land to reproduce. For them -- as for marine reptiles such as sea turtles, marine mammals such as seals and sea lions, and other pelagic seabirds such as auklets, guillemots, shearwaters and albatrosses -- secluded, secure sites on land are essential for survival. Yet for all the apparent immensity of the oceans, the number of suitable sites for breeding is limited to a precious and decreasing few.

Islands are the real-estate of choice for these groups, since isolation generally bestows security from predators such as rats, cats and foxes. After spending eight months or so at sea from autumn to spring, seabirds all over the world begin to move back toward their breeding grounds. Then, once spring conditions are suitable, they launch into their once-a-year rushed reproductive cycle.

Little-known and less-visited (see "Into the Unknown"; The Japan Times, July 28, 2002), the Sea of Okhotsk to the north of Hokkaido may be bountifully rich in plankton and fish, but it is surprisingly short on uninhabited sites where seabirds can breed in safety.

Tyuleni Island, where this tale began, is one such safe speck in this "unknown" sea -- safe, like this sea's other islands, largely due to its isolation, Russian restrictions on travel and the fact that they are unvisited by sports fishermen and have no fishing nets strung around them.

To the south, the coasts of Honshu and Hokkaido are dotted every few kilometers with buoys marking lines of nets strung far out to sea -- lines sometimes several kilometers long that constitute a wall of death for marine creatures inhabiting or visiting the coasts. Hence, it is hardly surprising that the populations of diving seabirds around northern Japan have plummeted as these nets have proliferated.

Each island in the Sea of Okhotsk has a different geological or topographical character and supports a somewhat different mix of species. The flat-topped slab of rock that is Tyuleni, for instance, hosts the region's largest colony of thin-billed murres -- hundreds of thousands of them. On the low cliffs on one side, some kittiwakes have settled, and a few pairs of tufted puffins have managed to burrow into the sparse clifftop soil, while on the beaches there are harems of Steller's sea lions and northern fur seals.

Nearly 1,000 km to the north is the conical plug of Iony. This is the Holy Grail for seabird biologists and students of Steller's sea lions. Here, black-and-white thick-billed murres occur in enormous numbers in summer, occupying almost every ledge and rock slab. In the jumbled rock piles on the island's slopes, there are auklet burrows, crested auklets mainly, but the species bird-watchers dream of sighting -- the whiskered auklet -- also lives among them. Meanwhile, higher up, a few fulmars, large gliding petrels, have found secluded ledges.

The jumbled rock piles of the Malmin Islands, lying closer to the sea's Siberian north shore, provide the perfect breeding habitat for the Sea of Okhotsk specialist, the spectacled guillemot. Though I count myself lucky to see two of the remnant population together in Japan, around the Malmin Islands I saw one flock of at least 800 birds -- and there were more.

Farther east along that same coast, the peaks of Nancikan rise like a jagged blade from the ocean. Too rugged and rocky for soil, Nancikan offers no home for burrowing birds. Even the murres seemed intimidated -- they need ledges large enough for their huge eggs. But black-legged kittiwakes build and glue a poop-deck of a nest to the smallest protuberance -- and Nancikan is kittiwake heaven. Swirls of them enshroud the island, flashing white, gray and black. It's truly a sight to behold when the immense colony rises, shrieking and panicking, as a massive soaring Steller's sea eagle appears, looking to pick off one or two for a meal.

Perhaps the most famous island in the Sea of Okhotsk is Talan, which has featured in at least one international wildlife documentary. Unlike all the other islands, this whale-back of rock is covered in rich vegetation, deep peaty soil, crags and talus slopes of jumbled rock. Talan is auklet paradise, and they are so common that their flocks swirl like smoke on wings so small that they whir audibly in flight.

But as the auklet legions scramble and scurry for their burrows, they run the gauntlet of the island's foxes. Winter sea ice allows these hunters to cross to and from the mainland, but on Talan the rock crevices are small and deep, providing refuge for the birds and preventing the foxes from doing serious damage.

So it is that each of the islands of the Sea of Okhotsk is unique in its qualities, supporting a different cast of seabird characters. Not just that, but each island is also a final stronghold for species that need their own safe space -- and likely couldn't find it anywhere else on Earth.