Background/Question/Methods
Lake Minnewaska, located in Minnewaska State Park near New Paltz, New York, was a fishless dating back almost a century. The lake’s food web has changed dramatically with the introduction of fish; Golden Shiners, a small minnow species, were introduced in 2008 and Largemouth Bass (LMB) were introduced in 2012. The LMB, with no natural predator in the lake, eliminated their food supply, Golden Shiners, by 2014 leaving LMB as the only fish species in the lake. Given the lack of fish prey for this primarily piscivorous fish, we asked if the LMB population size and individual health has been declining. In collaboration with the NY Department of Environmental Conservation, we caught LMB by electrofishing on two nights during each summer from 2012 to 2018. We marked the caudal fin of the LMB and two weeks later recaptured LMB to determine population size using Peterson’s method. In 2012, LMB were present, however, we did not catch enough (n = 4) for mark and recapture calculations. In 2018, we measured individual lengths, girths, and masses as indicators of individual health. To estimate age, we took scales from behind the pectoral fin and observed the rings indicating growth under a microscope.
Results/Conclusions
Each year, we collected and marked 40 to 100 LMB. LMB population size increased by 59% immediately after the loss of the Shiners, and, in the following years, LMB population size decreased by ~50% annually until 2016 with a population under 400. However, in 2017, the LMB population rebounded to 1,705 LMB in 2017 and stayed level 1574 LMB in 2018. In 2018, the LMB had an expanding population pyramid with 89% ranging from 1+ to 3+ years of growth. The average length of a 3+ year old Minnewaska LMB was less than the national average length expected for a 3+ year old LMB. Along with delayed growth, the girth and mass of the Minnewaska LMB, at any given length, were below the expected values for healthy LMB according to New York state standards provided by the DEC. Although the LMB population size has increased, there are many small bass that fall below the healthy standards with implications for the ultimate fate of the LMB population in this lake with a single fish species.