Introduced Tilapia Invade Nāpali Coast on Kaua‘i

August 9, 2019, 7:23 AM HST

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Thousands of black-chin tilapia have invaded near-shore waters in the Nāpali Coast State Wilderness Park on Kaua‘i. Fishermen first reported seeing large schools of mostly juvenile tilapia over the past two weeks. On Wednesday in-water surveys of the Nu‘alolo Kai section of the park confirmed the reports.

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Ka‘ili Shayler, a Fish & Habitat Monitoring Coordinator with the state Department of Land and Natural Resources’ Division of Aquatic Resources theorizes that they washed into the ocean from one of the ditch systems on the west side of Kaua‘i. Since they are considered mostly a freshwater species, he thinks they are moving to areas where freshwater flows into the ocean.

Authorities say this is “an unfortunate and dramatic example” of how invasive species, once introduced to Hawai‘i, can quickly take hold and ultimately out- compete native species for resources like food.

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Brian Neilson, DAR Administrator said, “While certain types of tilapia are fished or raised for human consumption there’s no place in our aquatic ecosystem for these invasive fish, particularly in the high numbers we’re now seeing on Kaua‘i’s north shore.”

Department officials called the proliferation an “emergency situation” and say they are working on issuing a special activity permit to gather community members to try and remove the tilapia with a surround net.

Shayler said, “We don’t want this species proliferating down the coast. We need to remove them before winter swells make it difficult or impossible to do anything.”

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Shayler used a throw net yesterday to catch five dozen tilapia, which were analyzed by aquatic biologists to see what they’re eating. Initial analysis showed that they’re currently consuming algae. The DAR team also took water samples to help determine the salinity of the ocean where the tilapia are schooling. This will help provide scientific data about their tolerance for saltwater versus freshwater.

DLNR Chair Suzanne Case echoed Neilson’s comments saying, “The Nāpali Coast State Wilderness Park is among the most pristine, in-tact, natural areas in all of Hawai‘i. It’s absolutely critical that we aggressively address any new invasive species threats and with this invasion of black-chin tilapia, that is precisely what we’re planning.”