Rainbow Trout Study Concludes

Posted on: December 14th, 2018 by Leslie_Zucker

Researchers from the U.S. Geological Survey (USGS), NYS Department of Environmental Conservation, and the firm EcoLogic concluded a study looking for one potential cause of recent Rainbow Trout population declines in the Ashokan Watershed.

The study was launched when the number of Rainbow Trout in the upper Esopus Creek, a major tributary draining into the Ashokan Reservoir, showed a precipitous drop between 2009 and 2013.

One potential cause for the decline was the establishment of two invasive fish in the reservoir – the Alewife established in the 1970s and White Perch in the 2000s. Both species are not native to the Ashokan Reservoir watershed and have the potential to change the type and abundance of food available to other fish, including Rainbow Trout.

Rainbow Trout captured in the upper Esopus Creek by Ed Ostapczuk.

Rainbow Trout captured in the upper Esopus Creek by Ed Ostapczuk.

The researchers did an analysis of fish caught in the Ashokan Reservoir over the past 70 years, looking at the rate of Rainbow Trout growth before and after Alewife and White Perch became established.

Surprisingly, the growth of Rainbow Trout appeared to increase over recent decades. The largest increases in both growth and condition of Rainbow Trout were observed after the introduction of White Perch. This was unexpected considering White Perch should be poor prey for Rainbow Trout and may also compete with Rainbow Trout for food.

The researchers did not conclude that White Perch in the reservoir benefitted Rainbow Trout. Instead, other changes in the watershed and its ecology may have affected the growth and condition of Rainbow Trout over the decades.

Future research and management may focus on identifying, protecting, and restoring areas in which Rainbow Trout spawn.

In further good news, annual electrofishing surveys at six sites on the Esopus Creek and its tributaries have shown that Rainbow Trout spawned very successfully over the past few years, according to George.

The AWSMP provided funding for this study through a Stream Management Implementation Program (SMIP) grant. A peer-reviewed article on the study was published in the October 2018 issue of the North American Journal of Fisheries Management. For more information see https://doi.org/10.1002/nafm.10203.