A recent story in Science features the innovative technique Western Association of Fish and Wildlife Agencies (WAFWA) members are using to help combat non-native fish species that are outcompeting native trout or other native species. The technique, known as the “Supermale” or “Trojan Male” approach, breeds male fish in hatcheries that carry only YY sex chromosomes – this means the YY males that are stocked into target areas will breed with females making all future offspring male. Over time, this reduces the number of females in the population ultimately ending the reproduction of the non-native fish in the system.

The Science article focuses on research published in July in the Transactions of the American Fisheries Society that was conducted by Idaho Department of Fish and Game (IDFG) personnel. The study on two headwaters creeks in Idaho documented how suppression of wild brook trout populations using hatchery produced YY males rapidly skewed sex ratios toward males, reaching 100% males within 6 years. The researchers found that when YY male stocking is combined with integrated electrofishing suppression, invasive brook trout can be eradicated from a system within a reasonable time frame.

“State fish and wildlife agencies recognized the need for a tool that would allow us to selectively remove invasive species while protecting native fish – the Trojan Male Fish approach does that,” says Lance Hebdon, Bureau Chief of Fisheries for IDFG.

“More evidence that the strategy works could arrive soon,” writes Science reporter Erik Stokstad. “Nine states contribute funding to a Trojan male fish breeding program at the Western Association of Fish and Wildlife Agencies, and eight states have active trials in streams. In New Mexico, the proportion of males in three experimental streams has reached up to 90%. And populations of native cutthroat trout appear to be rising, ‘which is really what we’re after,’ says Mikel Ruhl, a fisheries biologist with the New Mexico Department of Wildlife (NMDOW). The supermale project ‘will probably be the most impactful thing that I work on in my career,’ he adds.” 

WAFWA is leading YY Fish efforts due to our organization’s ability to coordinate and leverage activities by various member states and agencies using this technology. While YY brook trout are the first established and utilized brood stock, this approach has promise for a wide variety of species. Aligning the needs of various agencies for YY fish with production and development from participant brood stock sources allows all member agencies to benefit.

“WAFWA welcomes other states and organizations that would like to be part of the YY Fish Consortium to contact us,” notes Dr. George Schisler, WAFWA’s YY Fish Program Coordinator. “We are actively seeking additional partners and collaborators to help bring this technology into practical use for multiple other species.”