Unregulated fishing practices have left 75 percent of reef fishes depleted or in critical condition around the main Hawaiian Islands, according to new data on the condition of Hawai'i's reefs.

The declining fish stock also is disrupting the ecological balance of many reefs, which rely on herbivorous fish to keep algal growth in check, researchers say.

"We have a significant fishing problem in Hawai'i," said Alan Friedlander, fisheries ecologist with the Oceanic Institute. "Many species have been depleted, and there are things that need to be done in different areas to ensure the sustainability of our reefs."

Friedlander, along with marine ecologist Eric Brown of the Kalaupapa National Historical Park, presented the findings of a report titled "The State of Coral Reef Ecosystems of the Main Hawaiian Islands" yesterday at the Waikiki Aquarium.

According to the report, overfishing is just one of a growing list of pressures Hawai'i's coral reefs currently face, including rising sea temperatures, coastal development, pollution and invasive species. Nonetheless, Hawai'i's reefs are still relatively healthy compared to reefs in the Caribbean and the Atlantic.

Coral cover has been stable or improving in places such as Kaua'i's north shore and off Moloka'i, but is declining in more populated areas such as Kane'ohe Bay and Pupukea, Brown said.

The report, part of a larger effort by the National Oceanic and Atmospheric Administration to study the state of reefs in the United States and various Pacific regions, draws attention to Hawai'i's declining populations of targeted species of fish such as ulua, kumu, 'o'io and moi.

A separate study on the Northwestern Hawaiian Islands finds a relatively untouched environment, home to growing and stable populations of reef fish, green sea turtles and seabirds. Despite problems with marine debris and a declining Hawaiian monk seal population, the Northwestern Hawaiian Islands is still a good model of a natural and healthy ecosystem, Brown said.

Researchers examined population trends for 55 reef fish species in the main Hawaiian Islands compared to the virtually unfished Northwestern Hawaiian Islands, which served as a baseline for the study. They found that 42 percent of these species were in critical condition and 33 percent were depleted. Another 11 percent were below desired population levels, while just 2 percent were present in hyper-abundant levels.

The lack of local management, poor enforcement of existing regulations and harmful fishing methods such as gill nets have all contributed to smaller fish populations, according to the report.

In addition, researchers cited improved technology and an increase in the noncommercial catch of reef species by recreational and subsistence fishermen as factors affecting the declining fish stock.

"Some of these species are highly important as native food fishes," said Friedlander. They also play critical roles within Hawai'i's unique reef ecosystems, he said.

Without herbivorous fish grazing on reef algae, high levels of algae could smother and kill corals. In addition, many of these species cannot be replaced, should they become depleted.

"Some of these species are found here and nowhere else in the world. That's something that is very important to consider," Brown said.

Of the more than 7,000 marine plants and animals that inhabit Hawai'i's reefs, about 25 percent are found only in the Islands.

The state has taken efforts in recent years to protect Hawai'i's reef fish populations. In 2006, Gov. Linda Lingle approved regulations that required lay net registration and prohibited their use in some areas.

In addition, there are 34 state-managed Marine Protected Areas within the main Hawaiian Islands where fishing activities are limited.

Still, 89.5 percent of nearshore waters — waters less than 60 feet deep — are open to public fishing activity. About 3.6 percent of nearshore waters constitute partially protected MPAs, where some fishing is allowed.

Although protected areas are designed to conserve and replenish marine life, data from the new study show that partially protected MPAs have similar levels of fish populations as unrestricted areas. Fish populations in closed or no-take areas were comparable to those in community managed areas.

"This shows that centralized management doesn't work," said Friedlander, who believes that reefs should be locally managed. Community-based initiatives offer a solution to sustaining fish populations, he said.

"There is a lot of knowledge from people in the community that is untapped," he said. "The solution is bottom up as well as top down. Everyone's got a stake in this."