Title

Evaluation of compensatory responses to suppression of an invasive northern pike population in western Montana: implications for success

Presenter Information

William N. Glenn

Presentation Type

Presentation

Abstract

Northern pike is an invasive species of fish that was illegally introduced into western Montana. As with many other exotic predators, population suppression strategies were implemented to reduce their predatory impact on native species of concern such as cutthroat and bull trout. Suppression of established predator populations is controversial, because of the potential unknown compensatory responses that may limit success. Montana Fish, Wildlife and Parks (FWP) began removing northern pike from Milltown Reservoir in 2002 and continued until the removal of the reservoir was approved in 2005. Between 2000 and 2005, FWP collected diet data, scale samples, and abundance estimates. I examined whether lowering abundances through suppression increased individual compensatory growth response by examining northern pike scales and measuring the distances between yearly growth annuli. I used the Frasier Lee method to back-calculate size at age and found an average 30mm increase in the size of age 1 and age 2 fish following the beginning of suppression. Increased growth rates may result in higher reproductive capacity through a younger age of maturity and higher fecundity. In addition, increased growth rates of pike increased individual predation rates. Interestingly, with suppression of the pike population there was a decrease in the proportion of bull trout and cutthroat trout in the diets of northern pike. These trends are likely explained by the shift in size structure associated with removal of larger, adult pike to a population composed primarily of younger, smaller fish. Overall, the suppression strategy reduced predation on native trout, however without reducing numbers of smaller pike in the population the positive results are dependent upon suppression continuing.

Category

Social Sciences

This document is currently not available here.

Share

COinS
 
Apr 13th, 1:40 PM Apr 13th, 2:00 PM

Evaluation of compensatory responses to suppression of an invasive northern pike population in western Montana: implications for success

UC 330

Northern pike is an invasive species of fish that was illegally introduced into western Montana. As with many other exotic predators, population suppression strategies were implemented to reduce their predatory impact on native species of concern such as cutthroat and bull trout. Suppression of established predator populations is controversial, because of the potential unknown compensatory responses that may limit success. Montana Fish, Wildlife and Parks (FWP) began removing northern pike from Milltown Reservoir in 2002 and continued until the removal of the reservoir was approved in 2005. Between 2000 and 2005, FWP collected diet data, scale samples, and abundance estimates. I examined whether lowering abundances through suppression increased individual compensatory growth response by examining northern pike scales and measuring the distances between yearly growth annuli. I used the Frasier Lee method to back-calculate size at age and found an average 30mm increase in the size of age 1 and age 2 fish following the beginning of suppression. Increased growth rates may result in higher reproductive capacity through a younger age of maturity and higher fecundity. In addition, increased growth rates of pike increased individual predation rates. Interestingly, with suppression of the pike population there was a decrease in the proportion of bull trout and cutthroat trout in the diets of northern pike. These trends are likely explained by the shift in size structure associated with removal of larger, adult pike to a population composed primarily of younger, smaller fish. Overall, the suppression strategy reduced predation on native trout, however without reducing numbers of smaller pike in the population the positive results are dependent upon suppression continuing.