Tilapia Invasion Could Impact Local Fishery

Nile tilapia fish. DLNR photo.

An invasive species is overwhelming the Wailoa River system and could be impacting native fish populations in Hilo, according to the DLNR Department of Aquatic Resources (DAR). The Wailoa River system including its tributaries, Waiākea Stream and Waiākea Pond in Wailoa State Park, is seeing a burgeoning population of Nile tilapia—a species that was permitted for importation two years ago for fish farming operations.

Right now, officials are most concerned that the growing invasion will compete with native mullet populations, or ‘ama‘ama. The Wailoa River system is recognized as Hawai‘i’s prime mullet fishery and Nile tilapia could adversely affect the habitat and resources that maintain its standing.

A DAR team in Hilo led by aquatic biologist Troy Sakihara is seeking a solution to control flourishing population of Nile tilapia, including the possibility of an open fishing tournament. Sakihara and his team have been accepting both live and dead tilapia caught by fishermen and has noticed they are growing larger. For now, there are no restrictions or bag limits on Nile tilapia and biologists say people can catch and eat as many as they want.

The causes of the Nile tilapia invasion in Hilo are not yet known, but biologists caution that even minor lapses in aquaculture farming operation protocols could result in the current situation.

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

Two years ago, Nile tilapia were reclassified by the State Board of Agriculture as a restricted species for research only to allow them to be imported for fish farming at aquaculture facilities. While there is currently no evidence that the increasing presence of Nile tilapia in fresh water streams is related to commercial farming, it confirms fears that were expressed by DLNR leaders and biologists during Board discussions prior to the rule revision.

“Unfortunately, Hawai‘i 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 DAR Administrator Brian Neilson. “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.”