Fish Community and Population Response to Removal of Naturalized Smallmouth Bass in an Oligotrophic Adirondack Lake
Collaborators - Dan Josephson, Tom Daniel & Kurt Jirka (Cornell),with ongoing assistance from former graduate students Brian Weidel, Jason Robinson, Elise Zipkin and Jesse Lepak
Declines in native fish populations have been associated with the establishment of introduced smallmouth bass (Micropterus dolomieu) populations in the northeastern U.S. Introductions of non-native smallmouth bass have limited the abundance and diversity of native soft-rayed fishes, altered the trophic status of lake trout, and reduced brook trout biomass in Adirondack lakes and other northern waters. This study has demonstrated the potential for reversing the impact of a widely introduced, non-native fish predator in a large (271 hectare) Adirondack lake.
At the start of the new millenium (i.e. 2000) - following two years of pre-removal surveys - we initiated the removal of all smallmouth bass captured during Spring and Fall boat electrofishing surveys in the study lake; a similar removal effort was initiated in a smaller (100 ha) nearby lake in 2003. In the larger lake the relative abundance of six native littoral species increased (4-90 times pre-removal abundance) in response to smallmouth bass removal, and decreases in relative predation risk during the experiment reflected the reduction in littoral predators. A similar response was observed in the smaller lake, which is inhabited by fewer littoral species of fish. The population response of smallmouth bass to the intense harvest effort indicated that the population was resilient to removal, producing strong year classes throughout the experiment. Mechanical removal was successful at decreasing bass abundance and increasing native fish abundance, but has to date required ongoing annual harvest to maintain the fish community benefits of reduced abundance of large (i.e. > 150 mm) smallmouth bass. Our results provide experimental evidence regarding the need to prevent littoral predator introductions in Adirondack waters and offer support for nonnative control wherever native fish species conservation is a management priority.
As we continued to observe large annual recruitment of smallmouth bass following years of an intense bass removal effort, graduate student Elise Zipkin developed a density dependent, stage structured model to examine conditions under which population control through harvest could result in the increase of a targeted species. Parameter values were derived from a 54-year dataset collected from another north temperate lake (Lake Opeongo, Ontario, Canada) smallmouth bass population. Sensitivity analyses identified the demographic conditions that could lead to increased abundance in response to harvest. Of particular relevance to our intense removal effort, an increase in population abundance with harvest was most likely to occur when either: (1) per capita recruitment at low levels of spawner abundance was large, juvenile survivorship was high, and maturation of age-4 and older juveniles was moderately high, or (2) per capita recruitment at low levels of spawner abundance was slightly lower, yet the maturation rate of age-3 juveniles and adult survivorship were high. Our modeling results together with empirical evidence from Little Moose Lake further demonstrate the importance of understanding population overcompensation as a substantial factor to consider in efforts to regulate population abundance through harvest. Zipkin's work led to a broader analysis - across taxonomic groups - of population control control efforts where harvest has been employed to reduce the abundance of nuisance and invasive species. These results identify key issues that have been seldom recognized by managers that are potentially generic across a variety of taxa. We are continuing to use these model results to evaluate ways to further decrease smallmouth bass population abundance in our study lake, as well as understand ongoing population dynamics observed during the last decade.
For further information:
Lepak, J.M., C.E. Kraft and B.C. Weidel. 2006. Rapid food web recovery in response to removal of an introduced apex predator. Canadian Journal of Fisheries and Aquatic Sciences 63:569-575. [Link to Full article]
Weidel, B.C., D.C. Josephson and C.E. Kraft. 2007. Littoral fish community response to smallmouth bass removal from an Adirondack lake. Transactions of the American Fisheries Society 136:778-789. [Link to Full article]
Zipkin, E.F., P.J. Sullivan, E.G. Cooch, C.E. Kraft, B.J. Shuter and B.C. Weidel. 2008. Overcompensatory response of a smallmouth bass population to harvest: release from competition? Canadian Journal of Fisheries and Aquatic Sciences 65:2279-2292. [Link to Full article]
Zipkin, E.F., C.E. Kraft, E.G. Cooch and P.J. Sullivan. 2009. When can nuisance and invasive species control efforts backfire? Ecological Applications. Ecological Applications 19:1585–1595. [Link to Full article]