Long-term trends in Rainbow Trout growth and naturalized populations in the Ashokan Basin

Science Center Objects

Background: Rainbow Trout (Oncorhynchus mykiss) have thrived in the Esopus Creek since their introduction in the 1880s. The construction of the Ashokan Reservoir in 1915 changed the fishery by providing a stable lentic environment where adult trout could grow large and find refuge during periods when stream conditions become stressful. Although many adult Rainbow Trout spend time in the reserv...

Background: 

Rainbow Trout (Oncorhynchus mykiss) have thrived in the Esopus Creek since their introduction in the 1880s. The construction of the Ashokan Reservoir in 1915 changed the fishery by providing a stable lentic environment where adult trout could grow large and find refuge during periods when stream conditions become stressful. Although many adult Rainbow Trout spend time in the reservoir, it is believed that spawning occurs almost exclusively in the tributaries; most notably the Upper Esopus and its tributaries. Thus, the health of individual Rainbow Trout and the size of their spawning runs out of the Reservoir not only regulate the species’ future population in the reservoir, but also the population that reside in the Upper Esopus Creek, both of which are highly sought after by anglers.

There is a general consensus that Rainbow Trout populations across the basin have declined in recent years. Quantitative data collected by the USGS on the Upper Esopus Creek and its tributaries clearly show that density of Rainbow Trout populations generally declined from an average of 114 fish/0.1 ha in 2009 to 37 fish/0.1 ha in 2014. Limited gill netting data collected by the NYS Department of Environmental Conservation on the Ashokan Reservoir show a decline in catch rate from >1 fish per net-night in 1999 to 0.1 fish per net-night in 2013 (personal communication, Robert Angyal, NYSDEC, November 19, 2014). This is concerning because wild Rainbow Trout fisheries are rare in New York State and the fishery in the Upper Esopus and Ashokan Reservoir has historically been regarded as exceptional by sportsmen and managers. Additionally, trout species are generally considered to be indicators of good water quality and habitat (general ecosystem health); therefore, their declining populations are a serious cause for concern.

Objective: 

The objectives of this study are to (a) investigate causes of declining Rainbow Trout populations in the watershed, and (b) monitor the status of entire fish communities in the upper Esopus Creek and its tributaries.

Approach: 

The U. S. Geological Survey (USGS) and the Ashokan Watershed Stream Management Program (AWSMP) are collaborating on a study composed of two components to better understand long-term changes in the growth and abundance of Rainbow Trout in the watershed. For the first component, over 500 historical scale samples from Ashokan Reservoir Rainbow Trout collected between 1952 and 2017 are being examined to determine if the growth of Rainbow Trout has changed following introductions of two invasive fishes, Alewife (Alosa pseudoharengus) in the 1970s and White Perch (Morone americana) in the 2000s. Scale samples will be aged and prior lengths-at-age will be determined using back-calculation techniques. For the second component of the study, the USGS will conduct quantitative fish community surveys at 6 sites annually on the upper Esopus Creek and its tributaries. The resulting data will be used to compute community and population metrics of density and biomass to determine how fish assemblages have changed over time.

Results: 

Preliminary analyses indicate that:

  •    Growth of Ashokan Reservoir Rainbow Trout has increased over time
  • ·  The density of Rainbow Trout populations occupying the upper Esopus and tributaries declined markedly since 2009 but is showing recent signs of recovery

 Publications: 

George, S.D., and Baldigo, B.P., 2016, Long-term trends in naturalized rainbow trout (Oncorhynchus mykiss) populations in the upper Esopus Creek, Ulster County, New York, 2009–15: U.S. Geological Survey Data Series 992, 12 p., http://dx.doi.org/10.3133/ds992.

George, S.D., and Baldigo, B.P. , Flaherty, Michael J., Randall, Eileen A., 2018, Changes in Growth of Rainbow Trout in a Catskill Mountain Reservoir Following Alewife and White Perch introductions, North American Journal of Fisheries Management,  https://doi.org/10.1002/nafm.10203

Project
Location by County

Catskill Region: Delaware County, NY, Greene County, NY, Schoharie
County, NY, Sullivan County, NY, Ulster County, NY