9 Feb 2015

Ancient Fish Farming in Hawaii

By Shar Levine

What do science writers do when they go on vacation to the Big Island of Hawaii? If you are Shar Levine and Leslie Johnstone, you look for science at the beach.  At 'Anaeho'omalu Bay, or "A" Bay as the locals call it, the pair spent an afternoon at the anchialine ponds located between the Marriot Hotel and the beach.

Anchialine ponds are only found on two of the Hawaiian islands, Hawaii and Maui. These small inland ponds are found close to the ocean but are not connected to the surface of the sea. Salt water from the ocean seeps through the ground where it is mixed with fresh water flowing from the mountains. The pond is less salty than the ocean, but more salty than fresh water from a stream. The mixture of the two creates a unique "brackish" water for the fish living in the pond.

Anchialine Ponds, with "A" Bay in background

Hiding in the algae and water plants along the sides of the pond you can see shrimp, crabs, mollusks and tiny fish.  Much to the delight of tourists, an eel will sometimes poke its head out from the lava rocks in the waters just below the bridge connecting the pond to the beach. In the deeper section of the pond, large fish including amberjack and barracuda patrol the waters. The salinity of the pond varies with the depth and temperature of the water. Creatures who live in these waters are different from their relatives who live in the ocean and scientists are interested in studying how the fish have adapted to survive in this environment.

Types of fish found at "A" Bay pond

The ancient Hawaiians used these ponds as an early form of fish farming. There was very little work for the people to do. Small fish would enter the pond through a gated channel from the ocean to an outer pond. From there, the fish would thrive on algae and plants growing in the waters. The fish soon became too big to leave the pond through the gate. When the fish were adults,  they could easily be caught in a net and served for dinner.

The ponds form their own ecosystems. Here's how the food chain works:

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