Hawaii turns to traditional aquaculture to boost food security in the face of climate change

Hawaii turns to traditional aquaculture to boost food security in the face of climate change

By Joe Gasowski  

The small island archipelago of Hawaii, today imports over 85% of its food and in 2012 the Hawaii State House’s self-sufficiency bill, said that the islands were “dangerously dependent” on food imports. In fact, the most geographically isolated State in the U.S. only has domestic supplies of fresh produce to last ten days. This represents a substantial threat to the islands’ resilience to economic and environmental shocks and stresses, such as those posed by climate change. Today, in an effort to strengthen food security, Hawaiians are turning to traditional knowledge to restore the islands’ fishponds, providing a sustainable source of protein for Islanders and also restoring and protecting marine ecosystems.

Hawaii was not always so reliant on imports to sustain its people. In fact, in the early 1900s, it would even export large quantities of their food production abroad. Hawaii’s rich tradition of aquaculture dates back over 800 years and at one time the islands’ 488 fishponds were able to feed over a million Hawaiians. However, the islands were flooded with cheap US food imports in the later part of the 20th century, making key crops cheaper to import than to grow locally.

By 2010, Hawaii was importing over 50% of its seafood and around 85% of all its food. The focus of the economy had shifted to tourism, bringing with it considerable coastal development and urbanisation. The islands fishponds were left to decay. Today, just thirteen fishponds have been restored to some level and six are in active use. However, climate change, coastal erosion and the degradation of marine ecosystems have helped to spark a resurgence in interest in restoring the fishponds.

Building resilience through fishpond restoration

Climate change is driving significant changes to Hawaii’s ecosystems. Increasing water temperatures, saline intrusion in coastal areas and more erosion from storms and sea-level rise, are putting a strain on the marine environment and damaging other forms of agriculture. With increased incidence of drought and the degradation of the islands’ soils, aquaculture is becoming increasingly important as a source of food production.

The mounting threats to the Islands’ resilience caught the attention of local activists, such as Walter Ritte who have since then battled hard to rebuild the network of fishponds. In 2012 they helped pass state legislation to help speed up the legal processes that facilitate the restoration of fishponds.

Walter and other researchers on the islands, realised that the methods that to create the fishponds had many benefits for strengthening ecosystems. The process for creating a fishpond starts high in the mountains, where rivers flow through nutrient-rich forests. As the waters reach the lowlands, islanders plant fields of the root vegetable taro along the river’s path, and as the waters spread across the land they collect nutrients in mud and algae. The wider the rivers spread, and the slower the water moves, the more silt and mud is transferred to the coast, which is then used to combat erosion.

Image: Tarot is planted in wide fields adding nutrients to the waters that flow through them.

The fishponds themselves are stone circles built into the sea with specially designed mākāhā (gates) that allow fish to come in at high tide. The nutrient-rich river waters flow into these ponds, attracting small fish, which in turn attract larger fish to predate on them. Eventually, when the fish are ready to spawn, they leave the ponds, through the mākāhā at high tide. Local fishermen then capture the fish that they need, letting a proportion go back to the ocean to sustain stocks.

Image: The wall and gate of a fishpond under restoration in Kaloko-Honokōhau National Historical Park. Credit: National Park Service.

IOngoing climate challenges

Today though, the sustainability of the fishponds faces new threats from climate change. Reduced rainfall and increased temperatures have reduced the amount of fresh water on the islands, reducing river flow rates. At the same time, increased temperatures are making it harder to grow native plants including taro and warmer waters are disrupting delicate marine ecosystems.

Scientists from the University of Hawaii have been closely working with local communities to monitor in the He’eia fishpond on Oʻahu Island. Between 2004 and 2016, they are observing the consequences of climate change and the El Niño effect on the ecosystems around the fishponds. In 2009 there were two incidents that led to substantial numbers of fish dying in the ponds at He’eia; one in May and on in October. The researchers found that on both occasions, the mortality rates were the highest when there had been a drop in wind velocity and the surface water temperatures increased 2-3˚C higher than the baseline. This caused the hypoxia in the ponds, suffocating the fish. The unprecedented events show the significance of El Niño on Hawaii’s marine ecosystems. This type of El Niño impacting Hawaii has become 3 times more frequent in the last 30 years.

As climate change and its impacts are expected to worsen over the coming decades, researchers and local communities have been devising ways to adapt Hawaii’s aquaculture. Together they have come up with three ideas to lower the death rates of these fish:

  1. Moving the net pens closer to the mākāhā (gates) where the fish will be in higher water flows. The other gates can be used as a way of decreasing temperature in the fishponds and also to increase the aeration of these ponds and keep them breathing. 
  2. Install artificial aeration systems to oxygenate fishponds at times of highest risk (like during El Nino events).
  3. Changing the time of the fish harvest to be at the start of the heatwaves, reducing the potential for losses and allowing fish to escape into cooler oceans.

Other pressures such as pollution from human settlements are also being considered. On the island of Molokai, for instance, they are using swales to help filter polluted water and use wastewater to help irrigate crops.

Through these efforts, Hawaii’s fishponds are gradually being brought back to life, with 19 fishponds either in operation or being actively restored. The methods used by islanders have the potential to build the resilience of ecosystems in the face of considerable climate threats, as well as increase the food security of the isolated island archipelago.

Cover photo of Fishpond near He`eia of Oahu, Hawaii. Credit: State of Hawaii.

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