Nile tilapia have invaded Wailoa River system on Big Isle, state says

State officials say another tilapia invasion has occurred — this time Nile tilapia – in the waterways of Wailoa River State Park on Hawaii island.

The state Department of Land and Natural Resources says large schools of Nile tilapia are now visible in the Wailoa River system, including Waiakea Stream and Waiakea Pond in Hilo.

Just two month ago, state officials contended with the invasion of black-chin tilapia in the near-shore waters of Napali Coast State Wilderness Park on Kauai.

“Unfortunately, Hawaii has a long history of bringing in species, thinking that they’ll provide some commercial or ecosystem benefit, to discover later that these same species out-compete native species,” said Brian Neilson, DAR Administrator, in a news release. “We are now seeing stark evidence of this. While Nile tilapia were present in the Hilo waterways before aquaculture operations began, reports of Nile tilapia or hybrids are on the rise indicating that their population may be increasing, and their range may be expanding. That’s the real downside of bringing non-native species into the state for any reason.”

Two years ago, DLNR and Division of Aquatic Resources leaders had expressed concerns about the import of the species before the Hawaii Board of Agriculture. The board revised its rules, allowing the species to be imported for aquaculture facilities planning to farm-raise them.

Officials said there is no evidence that the recent “invasion” of the tilapia in fresh water streams has anything to do with commercial farming operations, and the reasons behind the current increase are unknown. Biologists, however, say all it would take is one lapse in biosecurity measures from an aquaculture farm to result in an invasion.

Hilo-based DAR aquatic biologist Troy Sakihara said the biggest concern right now is that the Nile tilapia are competing with the native mullet, or amaama, for habitat and resources.

Sakihara and his team have been taking in both live and dead tilapia caught by fishermen, and he noticed they grow large, and they grow fast.

“What makes them particularly troublesome as a potential invasive species, is they can survive and take over in a wide-variety of habitat conditions,” Sakihara said in the news release. “Their very hardiness makes them an issue.”

The DAR team in Hilo is in the process of determining what to do to control the burgeoning population of Nile tilapia, including the possibility of an open fishing tournament. As of now, they said fishermen can catch and eat as many as they want, given that there are no restrictions or bag limits on tilapia.