Invasive Fish Swarm Kaua‘i North ShoreAugust 9, 2019, 7:30 AM HST (Updated August 8, 2019, 6:07 PM)
An invasive species has been identified in droves off a popular coast of Kaua‘i.
Thousands of black-chin tilapia have invaded near-shore waters in the Nāpali Coast State Wilderness Park on Kaua‘i, according to a state Department of Land and Natural Resources (DLNR) press release. Fishermen first reported seeing large schools of mostly juvenile tilapia over the past two weeks.
On Wednesday, Aug. 7, 2019, a team from the DLNR Divisions of Aquatic Resources (DAR) and Boating and Ocean Recreation (DOBOR) conducted in-water surveys at the Nu‘alolo Kai section of the park and confirmed the reports.
“We first spotted several dead tilapia up on the rocky coastline at Nu‘alolo Kai,” said Ka‘ili Shayler, a fish and habitat monitoring coordinator with DAR. “After we conducted water sampling, we snorkeled several spots close to the shoreline and soon discovered literally thousands of fish in schools. While these might originally be viewed as an introduced species to Hawai‘i, they are definitely in this case an invasive species.”
DAR has received reports of additional tilapia invasions along the Nāpali Coast. Shayler theorizes that they washed into the ocean from one of the ditch systems on the west side of Kaua‘i, the release continued. Since they are considered mostly a freshwater species, he thinks they are moving to areas where freshwater flows into the ocean. The Nāpali Coast has many streams and waterfalls.
“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,” said DAR Administrator Brian Neilson. “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.”
DLNR plans to take aggressive steps to try and stop the invasive fish from moving further either direction, the release stated. Shayler and his colleagues are working on issuing a special activity permit to gather community members to try and remove the tilapia with a surround net.
“I consider this an emergency situation,” 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.”
Shayler used a throw net Wednesday to catch five dozen tilapia, which were analyzed by aquatic biologists to see what they’d been eating. Initial analysis showed that the fish are 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.