Hawaiʻi's ancient fishponds may help fish survive a warming ocean, according to research from the University of Hawaiʻi.
Long before modern aquaculture, Native Hawaiians built loko iʻa (fishponds) along the coastlines of every major island. These stone-walled ponds fed whole communities for generations. Now scientists are finding that the same systems may offer something we badly need today: resilience in the face of climate change.
What Are Loko Iʻa?
Loko iʻa are fishponds built by Native Hawaiians centuries ago, often where freshwater streams or springs meet the sea. Many are enclosed by a curved rock wall called a kuapā, with wooden sluice gates called mākāhā.
The design is brilliantly simple. Young fish slip through the gates to feed on the rich water inside. Once they grow too large to fit back through, they stay in the pond. Fish like ʻamaʻama (mullet) and awa (milkfish) thrived there, along with limu (seaweed), all without feed or fertilizer. It was a food system that worked with nature rather than against it.
What the Research Found
In a study published in npj Ocean Sustainability, researchers at UH Mānoa's Hawaiʻi Institute of Marine Biology compared water temperatures inside a loko iʻa with the surrounding bay, then modeled how fish populations might respond as the ocean warms. The work was centered on Heʻeia Fishpond on Oʻahu, and the team included loko iʻa practitioners alongside university scientists and resource managers.
What they found:
Fishpond populations held up better. As water temperatures rose, fish inside the loko iʻa declined less than fish in the surrounding estuary.
Freshwater is the key. The researchers credit the cooler, steadier temperatures to freshwater flowing into the pond, both from streams at the surface and from groundwater below.
Care makes a difference. Combining fishing rules, restored nutrient flow, and restocking helped offset some of the effects of warming and increased fish numbers over time.
In other words, a system designed by Hawaiian ancestors is proving to be one of the best tools we have for protecting fish in a changing climate.
Why It Matters Here
Fishponds are part of the story of Hawaiʻi Island too. On the Kona coast, Kaloko-Honokōhau National Historical Park protects some of the island's best-known loko iʻa, and community groups across the islands are working to restore ponds that fell into disrepair.
For me, this research is a reminder that caring for the ocean isn't only about new technology. Some of the best answers have been here all along, built stone by stone by people who understood these waters deeply.
How you can help:
Volunteer at a fishpond workday. Many restoration groups welcome volunteers to help clear invasive plants and rebuild walls.
Visit with respect. When you visit a loko iʻa, stay on marked paths and treat the walls as the cultural sites they are.
Support local and sustainable seafood. Choosing responsibly caught and locally raised fish helps keep Hawaiʻi's fisheries healthy.
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Source: Climate resilience found in traditional Hawaiian fishponds, University of Hawaiʻi News, November 17, 2025.
