By Jan TenBruggencate
Advertiser Columnist

The density of marine life in the Northwestern Hawaiian Islands is nearly three times greater than in the main islands.

That's one of the preliminary conclusions of a major survey conducted in 2000.

Scientists spent weeks in the 1,200-mile chain of islands to the northwest of Kaua'i as part of the Northwestern Hawaiian Islands Reef

Assessment and Monitoring Program, and they recently released their interim results.

One thing they found is that the density and diversity of fish life, and the size of fish within species, are quite different on those reefs than on the reefs around the main islands.

First, there is more life. The survey showed 260 percent more fish biomass, on average, than in the main islands. That may not be surprising on isolated islands without much fishing pressure. Perhaps more interesting is the mix of fish.

In the main islands, 48 percent of fish are plant eaters, and 49 percent are low-level carnivores — small fish that are meat-eaters. About 3 percent are "apex predators," including sharks, jacks (ulua) and groupers.

On the reefs of the northwestern islands, however, the apex predators make up more than half of the fish biomass — 54 percent. Herbivores are 27 percent and low-level carnivores are 18 percent.

Another feature of the northwestern islands is that all the fish are bigger than in the main islands. The survey attributes much of the difference to fishing pressure. One example cited is that of the spectacled parrotfish, or uhu uliuli.

The uhu is a favored fish for the table, and spearfishers have learned it's fairly easy to find and spear when sleeping. "As a result, this species has suffered from severe overfishing" and has become rare in the main islands, the report says.

The researchers found that this variety of parrotfish is quite common in the northwestern islands — 700 percent more abundant and on average 4 inches longer than those found in waters around the main islands.

The study makes two conclusions from all this. One is that there needs to be better management of reef fish in the main islands. The other is that the value of the Northwestern Hawaiian Islands must not be ignored.

These islands, "largely because of their remoteness, represent one of the last remaining large, intact and relatively pristine reef ecosystems in the world, and for this reason alone deserve our careful stewardship," the report said.

Details of the study are available on the Web.

Jan TenBruggencate is The Advertiser's Kaua'i bureau chief and its science and environment writer. Reach him at (808) 245-3074 or jant@honoluluadvertiser.com.