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.

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