Big, unique fish thrive in distant waters
By Jan TenBruggencate
Advertiser Science Writer
When Hokule'a crew members jumped into the water at La Perouse Pinnacle on their recent 1,200-mile voyage, the first things they saw were a huge black ulua and a pair of human-sized reef sharks.
The voyaging canoe Hokule'a was sailing an east-southeast course yesterday on its way from Midway Atoll to Hanalei Bay on Kaua'i. The vessel was south of Gardner Pinnacles yesterday afternoon, roughly 600 miles from Kaua'i.
The dramatic population of fish with big mouths and sharp teeth is what immediately strikes anyone who enters the water in the Northwestern Hawaiian Islands.
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When Hokule'a sailed northwest through the archipelago May 23 to June 9, divers among the crew saw very large ulua — 50- to 80-pounders — at every stop, and sharks on several occasions.
There also are lots of smaller, seaweed-eating fish, but in sheer size, the most impressive species are the ones that marine biologists call apex predators, including ulua, sharks, monk seals and groupers or hapu'u.
"Apex predators make up something like 58 percent of the biomass of the Northwestern Hawaiian Islands, compared to about 3 percent in the main Hawaiian Islands. The fish community looks top-heavy," said Randy Kosaki, research coordinator for the Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve.
"It's an indication of the impact of fishing pressure in our islands," he said.
At first, the balance of the fish seems impossible. How could the percentage of predators outweigh the prey?
Kosaki said studies are planned, but the best guess is that the coral atolls are such a productive ecosystem that prey replace themselves as fast as predators eat them.
And because the reef resources aren't being aggressively fished by humans, more food is available to the big fish.
One of the other interesting features about the atolls is that fish inhabiting deeper waters in the main islands are found in shallow water there.
The grouper is an example, he said. In the main islands, it is seldom seen in water shallower than 300 feet, but in the atolls, they show up at snorkeling depths of 20 to 30 feet.
The masked angelfish, normally found at depths of several hundred feet in the main islands, is another example. At Pearl and Hermes atolls, Kosaki pointed out a pair of masked angelfish in about 25 feet of water.
The atolls also are unique in their percentage of fish found nowhere else in the world. The term for this is endemism, and it refers to species that have evolved into new and unique forms in a particular region.
"As you approach the northern atolls, particularly Kure and Midway, the proportion of endemics increases," Kosaki said. He said about half the total number of fish present is endemic.
Some of the more unusual species are related to fish from southern Japan. Among these are the Japanese angelfish and two species of a reef fish called a knifejaw.
The Japan connection may be associated with the length of the Hawaiian archipelago, close to 1,400 miles from Hilo to Kure's Green Island. Kure and Midway are 1,200 miles closer to Tokyo than they are to Los Angeles.
Kosaki said the central islands, notably French Frigate Shoals, are home to giant table corals called acropora that are virtually never seen in the main islands.
The nearest reefs where these are found are on Johnston Atoll, 700 miles from Honolulu and less than 500 miles from French Frigate Shoals. Kosaki says young corals and other marine species may have drifted north from Johnston.
"Johnston is an intermediate stepping stone between Hawai'i and the South Pacific" for marine life looking for a shallow-water home, he said.
Advertiser Science Writer Jan TenBruggencate was a crew member aboard Hokule'a during its 18-day voyage through the Northwestern Hawaiian Islands from Kaua'i to Kure Atoll.
