For generations, native Hawaiians have understood that their aquaculture systems, fishponds known as loko i‘a, serve as nurseries that seed fish populations in surrounding waters. For the first time, a team of scientists from the Hawaiʻi Institute of Marine Biology (HIMB) have modeled this feat of Indigenous science in a study.
“We are using science to translate ‘ike kupuna, or Indigenous knowledge, into policy,” said study co-author Kawika Winter, an ecologist at HIMB and He‘eia National Estuarine Research Reserve (NERR). “The value of this paper is that it’s one of the first, if not the first, to really show that there are ways to do aquaculture in ways that benefit the system around it.”
In partnership with He‘eia NERR and Paepae o He‘eia, a nonprofit organization dedicated to stewarding the He‘eia loko i‘a, an ancient Hawaiian fishpond enclosing 36 hectares (88 acres) of brackish water, the team simulated different restoration scenarios in ‘Kāne‘ohe Bay on O‘ahu Island based on a simplified food web. The study found that restoring more of the bay into fully functional loko iʻa would grow fish populations not just within the ponds, but across the bay.
The Indigenous aquaculture systems found in Hawaiʻi have a unique design that supports the ecosystem in a way that commercial aquaculture doesn’t. There are six types of loko i‘a in Hawai‘i, each designed to complement existing features in the landscape.
The type of fishpond modeled in the study is called a loko kuapā, or walled fishpond, where a boundary rock wall encloses part of the ocean at the mouth of a nutrient-rich stream. By trapping nutrient-rich stream water, the enclosed space incubates phytoplankton, triggering algal blooms that feed herbivorous fish, thereby boosting herbivorous fish populations to levels much higher than in unmanaged estuaries.
Sluice gates, or mākāhā, are built into the wall to circulate water and allow young fish to move in and out of the pond, while separating larger fish from predators. The young fish leaving the pond often move into the bay’s larger ecosystem, where they become a food source for reef fish and fishers alike.
“In this way, the design manipulates preexisting natural conditions so that they’re extra productive,” said lead author Anne Innes-Gold, a marine biology Ph.D. candidate at HIMB. “Loko i’a are really built to work with the ecosystem, whereas not all forms of aquaculture are made to do that.”
Unlike commercial aquaculture, these traditional fishponds thrive without feed input and need little management once established.