Razorback sucker was listed as an endangered species in 1991. From 1985-1992 biologists estimated there were 300-600 of these fish left in the middle Green River, the last wild population in the Upper Basin. By 1999, researchers estimated the population had declined to about 100 adults and captures of larval fish declined. As a result, biologists began collecting the remaining adults from the Green River, as well as other locations, to establish a hatchery broodstock. Since the species had not been in hatcheries previously, biologists had to learn spawning and culture techniques, including the development of a diet specific for razorback sucker. By assessing survival rates after stocking, the Program refined methods for producing fish in a combination of indoor and outdoor facilities, as well as determining the best size and season to stock fish. After a decade of intensive effort and research, the stocking program was in place and releasing thousands of adult razorback sucker to the wild each year. As a result, razorback sucker in the rivers increased, as did numbers of larval fish in spring from wild reproduction.
As razorback sucker larvae increased in the river, the focus shifted towards improving survival of young fish spawned in the wild. Flow recommendations for Flaming Gorge Dam were modified in 2006 with the intent of benefitting fish. Peak flow releases in spring were timed to coincide with the Yampa River peak, in an effort to connect floodplain wetlands where young razorback sucker thrive. Further research looked at how well flows were timed to the presence of razorback sucker larvae and whether flow management was connecting the floodplains at the right time. This research found that releases typically occurred before larvae were present in the river, so that wetlands were often full or draining when larvae needed to access the habitat.
The result of these findings was the Larval Trigger Study Plan, or LTSP. The LTSP attempts to time dam releases when razorback sucker larvae are drifting in the river. Each spring, biologists set light traps to look for larval fish. When they find razorback sucker larvae in these traps, they inform the Bureau of Reclamation, who then schedule Flaming Gorge releases to reconnect floodplain wetlands. This flow release fills wetlands with water, and the water carries larval fish into the habitats. The LTSP was initiated in 2012, and since that time thousands of wild juvenile razorbacks have developed in these nurseries and been released back in the river. In 2020, remote antennas that detect tags in fish documented two of these wild-spawned fish near spawning sites in the middle Green River. Both fish were tagged in the Stewart Lake wetland and spawned in 2014. These age-6 fish represent the first known instances of wild razorback sucker recruitment to the adult stage since the species nearly disappeared from the Green River in the 1990s. And since razorbacks grow slowly and take several years to mature, we hope to see more of these LTSP fish show up in future monitoring. This progression of events shows how research and monitoring of fish populations can inform and improve management activities, such as hatchery production, to restore populations and improve outcomes in the wild. Through a significant investment of time and energy, and the dedication of biologists working