A new report says overfishing is the primary cause of reef fish decline in the state, according to the largest study of its kind every published; the study, “Human-induced gradients of reef fish declines in the Hawaiian Archipelago viewed through the lens of traditional management boundaries,” was published in the peer-reviewed journal Aquatic Conservation.
“The data was collected by multiple agencies and researchers since 2000, and is based on more than 25,000 in-water surveys,” said Dr. Alan M. Friedlander, a University of Hawaii marine ecologist, National Geographic’s Pristine Seas chief scientist and lead author of the paper. “This is the most compelling evidence that overfishing is the primary driver of reef fish declines in the main Hawaiian Islands, based on the most robust dataset ever put together for Hawaii, and perhaps the world.”
This findings in the study strongly suggest that fishing, rather than other human influences such as pollution or habitat degradation, is primarily responsible for the observed decline of reef fish. Data from the study clearly show that the abundance of food fish species (those primarily caught for human consumption) is lower in populated areas, while there is no difference in the abundance of non-food fish species (those not generally targeted by fishing) between populated and non-populated areas.
“There have been arguments for decades about the impacts of other factors on reef fish populations, such as sediment, sewage and physical damage to reefs,” said co-author Dr. Eric Conklin, marine science director for The Nature Conservancy of Hawaii. “But these threats would affect all fish similarly. The only impact that would affect food fish and non-food fish differently would be direct fishing pressure.”
That does not mean, according to Conklin, that we can ignore the impacts of nutrients, sediment and other threats to our oceans. “With climate change impacts predicted to increase in coming years, it is more important than ever to manage all the factors stressing our reefs, including overfishing,” he said.
The study found that off Oahu and Maui, where human population is greatest, the total amount of food fish species (e.g. uhu, ʻōmilu, kala) is a small fraction of those same species on remote reefs with small human populations (e.g. north Molokai, Kahoʻolawe, Niʻihau). What is eye-opening is that for non-food fish species (e.g. damselfish, butterflyfish, hīnālea), the total amount of fish is similar everywhere, including areas with high human populations and heavy fishing pressure.
The study also compared food fish populations between the Main and Northwestern Hawaiian Islands. “We found that food fish biomass was nearly three times higher in the Northwestern Hawaiian Islands compared to the Main Hawaiian Islands, and nearly 10 times higher than off Oʻahu and parts of Maui,” said study co-author Dr. Kuulei Rodgers of the Hawaii Institute of Marine Biology. “Biomass is a measure of the total weight of all fish in an area.”
Comparisons of 35 highly-prized food fish species revealed that the abundance of 14 of those species in the Main Islands was less than a quarter of that in the Northwestern Hawaiian Islands. According to Friedlander, as many as a third of Hawaii residents identify themselves as fishers, and fishing pressure is understandably much greater in areas with higher human populations.
“Many important food fish species have declined by more than 75 percent across the populated Hawaiian Islands,” Friedlander said. “This rate of loss can’t persist if we want to continue fishing–and eating–reef fish in our islands.”
We can, however, restore abundance to Hawaii’s nearshore fisheries. “Marine protected areas are a proven way to restore declining fish populations in Hawaii and around the world,” Friedlander said. “They need to be well designed, effectively managed and large enough to protect valued species, so that they can mature and produce large numbers of offspring.”
Another proven solution is community-managed fisheries, like the ones recently established in Hāʻena, Kauai and Kaʻūpūlehu, West Hawaii. Community-based resource management areas can harbor fish biomass similar to that in no-take reserves, the study revealed.
“This research also shows the value of managing fisheries at the moku (district) scale, the traditional unit of resource management, rather than the smaller ahupuaʻa (watershed) or larger island scales,” said co-author Rodgers.
“The ocean provides so much to the people of Hawaii, such as food security, recreation, and cultural identity, but the health of Hawaii’s marine environment is at a critical juncture,” Friedlander said. “This study suggests that future marine resource management in Hawaii might benefit from the long history of knowledge and past practices that sustained people and the ocean for centuries.”
Image courtesy The Nature Conservancy of Hawaii