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History of Fish Presence and Absence Following Lake Acidification and Recovery in Lake Minnewaska, Shawangunk Ridge, NY
David M. Charifson, Paul C. Huth, John E. Thompson, Robert K. Angyal, Michael J. Flaherty, and David C. Richardson

Northeastern Naturalist, Volume 22, Issue 4 (2015): 762–781

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Northeastern Naturalist 762 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 22001155 NORTHEASTERN NATURALIST 2V2(o4l). :2726,2 N–7o8. 14 History of Fish Presence and Absence Following Lake Acidification and Recovery in Lake Minnewaska, Shawangunk Ridge, NY David M. Charifson1, 2, Paul C. Huth3, John E. Thompson3, Robert K. Angyal4, Michael J. Flaherty4, and David C. Richardson1,* Abstract - Lake acidification is a major problem in northeastern US lakes that can control fish presence or absence. We examined the history of fish populations in Lake Minnewaska, in eastern New York. We examined historical documents and found that Lake Minnewaska was fishless from 1922–2008 because of high lake-acidity. Following 30 years of recovery from acidic conditions, Notemigonus crysoleucas (Golden Shiner), a small minnow species, was introduced in 2008 and quickly proliferated, peaking at ~15,000 individuals in 2013. In 2012, the piscivorous species Micropterus salmoides (Largemouth Bass) was introduced, and the minnow population was effectively removed by 2014. We present a conceptual model of the history of fish in Lake Minnewaska as fish disappeared and reappeared over 100 years as a consequence of acid rain and human introductions . Introduction Fish communities are integral components of most aquatic ecosystems and play key roles in linking lower trophic levels to top predators within and outside of their aquatic boundaries (Vander Zanden and Vadeboncoeur 2002). Fish communities also provide ecosystem goods and services on which humans rely (Palmer and Richardson 2009). Species presence and population size are cont rolled by both biotic and abiotic factors, with spatial scale playing a strong role in mediating these dynamics (Jackson et al. 2001). The community of fish species able to migrate to any given lake is ultimately controlled by the regional-species pool and anthropogenic introductions. Biotic and abiotic factors in lakes regulate the presence of fish species from the regional pool as well as the growth of each population. Biotic factors include bottom-up controls via reduction or increase in food sources, and top-down controls via predation and interspecific competition (e .g., Trumpickas et al. 2011). There are 3 categories of abiotic factors that control fish communities: physical habitat and habitat accessibility, climatic factors, and water chemistry, including dissolved oxygen and acidity (Beisner et al. 2006, Jackson et al. 2001, Jeppensen et al. 2010). Lake acidity is particularly important in determining fish species presence/ absence and fish-community structure, depending on species’ tolerance for low 1Biology Department, SUNY New Paltz, 1 Hawk Drive, New Paltz, NY 12561. 2Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY 11790. 3Mohonk Preserve, PO Box 715, New Paltz, NY 12561. 4New York State Department of Environmental Conservation, 21 South Putt Corners Road, New Paltz, NY 12561. *Corresponding author - Manuscript Editor: Craig Purchase Northeastern Naturalist Vol. 22, No. 4 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 763 pH. Acidity can cause deleterious physiological and behavioral responses and the extirpation of fish populations through direct fish kills, especially those species sensitive to decreasing pH (Matuszek et al. 1990). With slow increases in acidity, fish experience behavioral modifications, morphological deformities, and impairment of chemoreception (Mount 1973, Ore et al. 1997). For example, Pimephales promelas Rafinesque (Fathead Minnow) can survive at pH 5–6, but behavior is abnormal, swimming patterns are modified, and stress levels appear to increase (Mount 1973). At pH < 6, morphological deformities appear; male Fathead Minnows may be hunch-backed and have smaller-than-average heads (Mount 1973). For multiple species, fish reproduction is sensitive to lake acidification; reduced egg production and viability have been documented when pH < 6 (Eaton et al. 1992, Mount 1973). Lake acidification in the northeastern US became a problem in the 19th and 20th centuries following industrial intensification at local and regional scales and continual increases in anthropogenically driven sulfate and NOx emissions to the atmosphere (Likens et al. 2005). Anthropogenic emissions cause decreases in the pH of precipitation, and prevailing west-to-east winds push the acidic fronts to the Northeast. Acidic precipitation has been a problem for fish populations, and some communities in acidified lakes have lost species richness or entire fish populations (e.g., Driscoll et al. 1991). The potential for impacts of lake acidification are moderated by the underlying geology in the watershed and the lake’s position in the landscape (Driscoll et al. 2003a, b). For example, lakes located on quartz or granite bedrock are more susceptible to acidification than those on shale or carbonate-rich lithology with high inherent buffering capacity. In the northeastern US, there are over 7000 lakes with underlying geology that make them susceptible to acidification as a result of acid rain (Brakke et al. 1988). Since enactment of the 1990 Clean Air Act amendment, there has been a general increase in the pH of rain across the Northeast, resulting in moderate recovery of susceptible, acidified lakes (Greaver et al. 2012). Lake acidification in the Sudbury region of Ontario, Canada, is well-studied and provides many interesting parallels to our study system, Lake Minnewaska, and the other lakes of the Shawangunk Ridge, NY. Mining and smelting operations in Sudbury were extensive, and released copious amounts of sulfur and trace-metal emissions into the air, which led to acidification of both local and regional aquatic systems (Dixit et al. 1992a). The lakes of Killarney Provincial Park in the La Cloche Mountains, nearby Sudbury, have thin, sandy soils, with quartzite bedrock that provided little buffering capacity to overlaying aquatic systems, increasing their susceptibility to acidification (Dixit et al. 1992a, b; Keller et al. 2003). A study of 3 lakes in Killarney Provincial Park estimated the progression of and recovery from acidification during the period spanning the pre-industrial period to the late 1980s using diatom and chrysophyte records in sediment cores as environmental indicators (Dixit et al. 1992b). The 3 lakes were generally slightly acidic with pH values of ~5.5–6.2 prior to industrialization. They started to acidify further around 1920– 1930, reached a pH minimum (pH ≈ 4 for the most acidic of the studied lakes) Northeastern Naturalist 764 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 Vol. 22, No. 4 between 1970–1980, and began to recover soon after (Dixit et al. 1992b). Lakes far to the east of Sudbury in the Atlantic Provinces of Canada were also acidified, but have not shown nearly as much recovery, despite large decreases in acid deposition (Clair et al. 2011, Jeffries et al. 2003). Fish populations were greatly altered by acid deposition in the lakes near Sudbury, Canada (e.g., Beamish 1974, Gunn and Keller 1990). However, biological recovery has been noted in many of these lakes. For example, in 1980, Whitepine Lake (pH of <5.5) contained abundant Perca flavescens Mitchill (Yellow Perch), an acid-tolerant species, but sensitive species like Salvelinus namaycush Walbaum (Lake Trout) and Catostomus commersonii Lacépède (White Sucker) were rare and not able to reproduce (Gunn and Keller 1990). With increases in pH and buffering capacity, Lake Trout began to reproduce in the lake in 1982; the catch-per-effort rate for juvenile Lake Trout increased by a factor of 50 from 1982 to 1987 (Gunn and Keller 1990). Similarly, the lakes across New York State, especially in the Adirondack and Catskill mountain ranges, have been affected by the increase and more-recent decrease of acid rain. Adirondack mountain lakes are susceptible to acid rain because of weather patterns that deposit large volumes of low-pH precipitation in lakes with little acid-buffering capacity due to underlying bedrock geology (Driscoll et al. 2003b). Paleolimnological evidence supports that this acidification occurred between the 1920s and 1970s (Charles et al. 1990). In the Adirondacks, the proportion of lakes with low pH and without fish went from 4% in the 1930s to 46% in the 1970s (Schofield 1976), but recovery has taken place since the implementation of the 1990 Clean Air Act amendment. The percentage of acidic Adirondack lakes with acid-neutralizing capacity of <0 μeq L-1 has dropped from 15% down to 8% of all lakes (Waller et al. 2012), with implications for the recovery of fish populations. For example, Honnedaga Lake lost acid-sensitive fish from 1920 to 1960, leaving only Salvelinus fontinalis Mitchill (Brook Trout) extant until the late 1970s when the Brook Trout were extirpated from the lake (Josephson et al. 2014). Following recovery from acid rain and associated changes in water chemistry through the 1990s, Brook Trout were able to recolonize Honnedaga Lake by 2000, although there has been minimal recovery of other acid-sensitive species like White Sucker (Josephson et al. 2014). Similar to lakes in eastern Canada and the northeastern US, waterbodies along the Shawangunk Ridge (Fig. 1), at the foot of the Catskill Mountain range in southeastern New York, have also experienced extirpation of fish populations as a direct result of local and regional acid rain. The aim of our research was to examine the history of fish presence and absence in Lake Minnewaska, one of 5 sky lakes on the Shawangunk Ridge. Fish reappeared in Lake Minnewaska in 2008 following 86 y without fish due to acidic lake waters. We had 2 specific research objectives with different methodological approaches. First, we wanted to determine how fish-population size and composition changed in Lake Minnewaska between the late 1800s and 2008. Scientific data was lacking for much of that period; thus, we examined reports, historical documents, and personal anecdotes to elucidate Northeastern Naturalist Vol. 22, No. 4 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 765 the history of fish in Lake Minnewaska. Second, following the fish reintroduction in 2008, we sought to describe changes in fish population size, age structure, and species composition. We established a scientific protocol for evaluation of fish-population and community dynamics, including the evaluation of population size via catch–mark–recapture techniques. We measured, aged, and identified fish for several years. Herein, we present a general conceptual model of the history of fish in Lake Minnewaska as fish appeared, disappeared, and reappeared over more than 150 y as a consequence of acid rain and human introductions. This conceptual model helps to establish a context and goals for management decisions regarding fish introduction in the other Shawangunk Lakes. Site Description Lake Minnewaska (41°43'41''N, 74°14'10''W) is one of 5 glacial sky lakes located in the Shawangunk Ridge of southeastern New York (Fig. 1). The sky lakes (Maratanza, Haseco, Awosting, Minnewaska, Mohonk; Fig. 1) lie atop the Shawangunk Formation, which is composed of weathering-resistant quartz-conglomerate of middle Silurian age (Epstein 1993). This bedrock produces shallow, acidic soils, and releases few acid-neutralizing ions into surrounding waters, similar to lakes with underlying quartzite bedrock in Killarney Provincial Park, ON (Dixit et al. 1992a, b). The Shawangunk conglomerate lies above the Ordovician Martinsburg Formation and is composed of shale beds (Epstein 1993). Lake Minnewaska is glacial in origin—it was gouged out during the last glacial retreat (Peteet et al. 2009). The lake has a surface area of 18.6 ha, a maximum depth of 23.4 m (Fig. 1), and an elevation of ~503 m above sea level. The Lake Minnewaska watershed is small; the lake itself contains ~45% of the total surface area of its watershed (Kiviat 1988). The lake has no inlets and only a single outlet that has intermittent surface-flow. These characteristics make Lake Minnewaska primarily rain-fed, and therefore sensitive to acid precipitation. Methods History of fish in Lake Minnewaska The Smiley family, founders and owners of the Mohonk Mountain House since 1869, have collected observations of fish in Lake Minnewaska over the past 145 years. Daniel Smiley compiled records and stories from local historians, researchers, and ecologists, and consulted with fisheries experts at the regional office of the New York State Department of Environmental Conservation (NYSDEC). We have synthesized these and other historical records into a conceptual framework of the history of fish in Lake Minnewaska with bounds on fish presence prior to our study. We include a history of fish in both Lake Minnewaska and a nearby sky lake, Awosting, which is currently fishless. The conceptual framework for fish occupation of Lake Minnewaska (Fig. 2) includes high uncertainty for fish presence and population sizes based on lack of scientific data. Northeastern Naturalist 766 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 Vol. 22, No. 4 Figure 1. Location of the Northern Shawangunk Ridge and Lake Minnwaska (black diamond) in the Hudson Valley, NY (41º43'41''N, 74º14'10''W. The sky lakes (top inset) are highlighted in circles from southwest to northeast: lakes Maratanza, Haseco, Awosting, Minnewaska, and Mohonk. Data and topographic map for this inset from Google accessed 14 May 2015. Lake Minnewaska bathymetry (bottom left inset) depths are in 4-m intervals with the deepest location in the northern part of the lake (ope n diamond) at 23.4 m. Northeastern Naturalist Vol. 22, No. 4 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 767 Catch–mark–recapture During 2012–2014, we measured total length of fish captured via net-seining and electrofishing in Lake Minnewaska as described below. In 2013 and 2014, we estimated fish-population sizes in Lake Minnewaska using catch–mark–recapture techniques. Only 2 fish species have been found in the lake during the past 6 years: Micropterus salmoides Lacépède (Largemouth Bass) and Notemigonus crysoleucas Mitchill (Golden Shiner). We marked both species by clipping the dorsal portion of the caudal fin. Under laboratory conditions, swimming ability was not obviously affected by fin clips, and the mark was clearly noticeable for 1.5 months. During summer 2013, we initially caught fish by seining multiple times at several locations. We recaptured fish by electrofishing. In summer 2014, we employed electrofishing techniques for both the capture and recapture phases. For electrofishing, we used a Smith-Root 4.9-m electrofishing boat (Smith-Root, Vancouver, WA) with 2 bow scrapers during each collection run. We operated the electrofishing boat at 1000V, 120 pps DC drawing 5A for all samples, with the exception of the 17 June 2014 sample when the boat was inadvertently operated in AC mode. Operating in AC may be less efficient, resulting in a decreased catch/effort, but since this was the marking run of a mark–recapture sample effort, the change did not affect the final fish-population estimates. We conducted all sampling beginning roughly at sunset, and each run consisted of a minimum of 1 circuit of the shoreline of Lake Minnewaska. The habitat for Largemouth Bass and Golden Shiner is better along the southern shore; thus, we often made another pass up that shore in an attempt to collect more fish. However, each time we did this, the habitat-specific catch rate for both species appeared to decline from the earlier pass. Additionally, on 30 June 2014, we made 1 linear run up the middle of the lake and back with the objective of sampling any pelagic Golden Shiners that may have been present. We completed all electrofishing by 23:00. We calculated population-size estimates (N) using Peterson’s method (Krebs 1998) such that N = ([M + 1] [C + 1] / [R + 1]) - 1, Figure 2. Conceptual model of fish presence in Lake Minnewaska with the yaxis representing relative fish abundance. The shaded region represents relative fish abundance with thickness indicating uncertainty, based on anecdotal evidence and historical records prior to 2012 and population estimates after 2012. The horizontal line between 1922 and 2008 indicates total absence of fish. Northeastern Naturalist 768 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 Vol. 22, No. 4 where N is the population size, M is the number of initially marked individuals, C is the sample size of the recaptured individuals, and R is the marked, recaptured individuals. We determined 95% confidence intervals using the Poisson distribution due to a small number (<10%) of recaptures relative to fish marked originally (Krebs 1998) as follows: CI = ([M + 1] [C + 1] / X) - 1, where X = 1.051 for the upper 95% confidence limit and X = 6.323 for the lower 95% confidence limit. We used a t-test to compare the estimated population size between 2013 and 2014 for each species. We compared average-fish length among years (2012–2014) using either a 2-sample t-test when 2 years of data were available or a 1-way ANOVA when more than 2 years of data were available. We conducted all statistical analyses and verification that the data met assumptions of normality with the R statistical package (R Core Team 2013). Age estimation from scales To estimate fish age, we collected scale samples from behind 1 of the pectoral fins of a subset of Largemouth Bass and from between the dorsal fin and the lateral line of 5 Golden Shiners per cm–length group. We heat-pressed scale samples into acetate plastic, and inspected them under magnification with a microfiche reader. We estimated ages by counting annular marks on the individual scales, following the general methods described by Jearld (1983). We were confident that our Largemouth Bass age estimates were accurate. However, NYSDEC staff in this region typically do not age Golden Shiners, so our experience with this species was very limited. We noted apparent check marks in the pattern of circuli on some of these samples that did not exhibit the spacing expected from true annuli; thus, the age estimates of Golden Shiner should be used with some caution. We applied a simple linear regression between fish size and age for each species to derive an equation for converting mean size to age in each year. Changes in limnological parameters following fish intr oduction We compiled all available limnological (physical, biological, and chemical parameters) data—including pH, Secchi depth, chlorophyll a (chl a) concentration, total phosphorus (TP) concentration, specific conductivity, and occurrences of anoxia in the hypolimnion prior to and following fish introduction in 2008—from primary-literature sources and New York State reports for Lake Minnewaska. In 2012 and 2013, we measured the above variables at 4 shallow locations around the edge of the lake and at the deep site in the surface waters (Fig. 1). We used standard spectrophotometric methods for chl a and TP concentrations (Richardson et al. 2014). We averaged all data prior to fish introduction (1922–2008) and post fish introduction (2009–2014), and when data was available for the period prior to 2009, we performed a 2-sample t-test to test the difference of limnological variables before and after fish introduction. Northeastern Naturalist Vol. 22, No. 4 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 769 Results Local and regional acid rain in the Shawangunk Ridge Industry, both locally and regionally, was increasing rapidly in the early 20th century and might have contributed to decreasing air quality resulting in the acidification of the lakes. There were many potential sources of air pollution to the south and west of the Shawangunk Ridge that, following prevailing wind patterns, passed over the sky lakes. During the 19th century, the regional demand for wood products exploded to support industrial growth, and settlers were hired to cut Shawangunk Ridge forests for tanbark, barrel-hoop poles, charcoal production, and cordwood harvest (Josephson and Larsen 2013, Thompson and Huth 2011). Charcoal production and deforestation occurred across the Ridge and likely resulted in poor air quality and transport of heavy particles over short distances from the earth-mound and pit-kiln charcoal-production fires (e.g., Pennise et al. 2001, Straka 2014, Thompson and Huth 2011). There was substantial zinc, lead, and copper smelting within 10 km of Lake Minnewaska in Ellenville, NY, where forges and iron blastfurnaces worked 24 h per day (Josephson and Larsen 2013, Thompson and Huth 2011). During the 19th and 20th centuries, the railroads expanded on both sides of the Shawangunk Ridge, and the fuel load for the furnaces switched from locally harvested wood and charcoal to coal and coke, which is a high-carbon–content fuel manufactured from coal (Josephson and Larsen 2013). Industrialization expanded nationally throughout the early 20th century, and many lakes became increasingly acidic (Likens et al. 2005). History of fish in Lake Minnewaska prior to 2008 Lake Minnewaska and all of the other sky lakes are glacial in origin with waterfalls along their outlet streams that restrict fish migration. Fish dispersal into Lake Minnewaska was probably prevented by these geographic barriers despite the likelihood that pH was high enough for fish survival and reproduction. However, there is historical evidence that fish were present in the sky lakes during the 19th century, possibly due to introductions by humans (Table 1). A reasonable alternative is that for a period following the retreat of the last glacier, the landscape did not contain geographic barriers to fish dispersal into the lake. The first non-indigenous settlement and forestry activity on the Shawangunk Ridge dates to about 1799. There is little record of land use in the early 1800s. In the mid-1800s, George Davis, a settler, owned Lake Minnewaska but rarely saw it, indicating that he did not use the lake for fishing before selling the property and lake to Alfred Smiley, owner of the nearby Mohonk Mountain House (Josephson and Larsen 2013). Calvin Burger, a hunting guide on the mountain, had a boat on the lake prior to the sale of the lake and land to Alfred Smiley (Josephson and Larsen 2013); it is possible that he fished for sustenance or as recreation for visiting (and paying) tourists. It is unlikely that the Smiley brothers stocked the lake with fish from Mohonk given that they would have recorded it in their meticulous naturalist records (e.g., Cook et al. 2008). Prior to the 20th century, loggers or stonecutters could have stocked Lake Minnewaska with several species of fish as a food source for nearby logging camps. Similar procedures have Northeastern Naturalist 770 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 Vol. 22, No. 4 been documented for other sites in northern New York and New England where logging companies sent teams to stock nearby lakes with easily caught fish species for food at the camps a decade before logging an area (Brokaw and Lucas 2008). This possibility is supported by the documented 19th-century presence in the sky lakes of 2 fish species that were often used in stocking lakes and ponds for logging camps— Esox niger Lesueur (Chain Pickerel) and Yellow Perch (Table 1; Brokaw and Lucas 2008). The date of the last fish recorded in Lake Minnewaska was in 1922 when 300 Yellow Perch were collected following the dynamiting of the lake to retrieve a drowning victim (Table 1, Fig. 3). After that, Lake Minnewaska and the other sky lakes were too acidic to support the fish populations. In 1957, for example, 1500 trout from various species were stocked in nearby Lake Awosting, which had acidity similar to that of Lake Minnewaska; within 4–5 days, most of the trout were dead (Smiley and Huth 1983). Reintroduction of fish in 2008 In 2008, individual Golden Shiners were first spotted in Lake Minnewaska, and the population increased rapidly over the next few years until schools of the fish were visible to all visitors to the lake (D.C. Richardson, pers. observ.). Golden Shiners may have been dumped in 2008 as leftover bait fish from a day of unsuccessful fishing at Lake Minnewaska or introduced through illegal stocking. In 2012, we observed clear populations of Golden Shiners in the shallows around the entire lake that were easy to catch via beach seining. In 2013, we estimated the Golden Shiner population size at 15,320 ± 5300 (mean ± SE); however, in 2014, we found no Golden Shiners. This result represents an abrupt and statistically significant decrease (t = 3.35, P < 0.001, df = 327; Fig. 4). We first observed Largemouth Bass in 2012. We surmise that in 2012, Largemouth Bass were dumped as fry or as larger fish by an angler who saw a possible fishing location with sufficient prey species to support a bass population. The Table 1. History of fish presence in 2 lakes on the Shawangunk Ridge. For the column labeled Verifiable, Yes = an account with photographic or written record (primary source) for the given time and species and No = anecdotes of local people or a written secondary source. Dates prior to 2009 are from Smiley and Huth (1983), dates after are the observations o f the authors. Lake Minnewaska Lake Awosting Year(s) Species present Verifiable? Year(s) Species present Verifiable? 1878 Trout spp.A No 1878 Yellow Perch Yes 1879 Chain Pickerel No 1889 Chain Pickerel Yes Prior to 1914 Yellow Perch No 1889 Yellow Perch No Prior to 1914 Chain Pickerel No 1901–1903 Chain Pickerel No 1922 Yellow PerchB Yes 1909C Chain Pickerel No 2009–2013 Golden Shiner Yes 1956D Trout spp. Yes 2012–present Largemouth Bass Yes A7 individuals found dead; only known occurrence of this species at Minnewaska. BLast known occurrence of fish at Lake Minnewaska, prior to reint roduction in 2009. CLast recorded natural occurrence of fish at Lake Awosting. DLake Awosting was stocked with 1500 trout from various species. Nearl y all died within 5 days. Northeastern Naturalist Vol. 22, No. 4 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 771 population across all size classes of Largemouth Bass increased from 869 ± 471 (mean ± SE) individuals in 2013 to 1380 ± 770 in 2014. Although the population increased by 60%, this difference was not significant (t = 0.54, P = 0.59, df = 157; Fig. 4) due to a large standard error caused by the small number of individuals recaptured. Figure 3. Photograph of the last known fish in Lake Minnewaska prior to reintroduction in 2008 showing ~60 Yellow Perch of the 300 that died following dynamiting of the lake to recover a drowning victim in 1922. Published with permission from the Mohonk Preserve, Alfred F. Smiley collection. Figure 4. Populationsize estimates of N. crysoleucas (Golden Shiner) and M. salmoides (Largemouth Bass) in Lake Minnewaska. Dark gray and light gray are 2013 and 2014, respectively. Error bars represent 95% confidence intervals constructed using the Poisson distribution. No Golden Shiners were found in 2014. Northeastern Naturalist 772 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 Vol. 22, No. 4 Mean Golden Shiner size was 82 ± 19.7 mm in 2012 and 90 ± 14.0 mm (mean ± SD) in 2013, a significant increase in mean fish size (t = -3.3, df = 104, P = 0.001; Fig. 5). Golden Shiner length (mm) was positively and linearly related to fish age (y): 0.022–0.25 (fish length) (F1, 67 = 47, P < 0.001, r2 = 0.41; Fig. 6). Using the length–age regression yielded average-age estimates of 1.5 years in 2012 and 1.7 years in 2013. Mean Largemouth Bass size was 149.8 ± 113.0 mm, 113.1 ± 68.0 mm, and 168.8 ± 61.2 (mean ± SD) in 2012, 2013, and 2014 respectively (Fig. 7). Size was a significant main effect (1-way ANOVA: F2,203 = 39, P < 0.001) with posthoc means comparisons indicating that mean size significantly increased from 2013 to 2014 but neither 2013 nor 2014 were different from 2012 likely due to small sample size (n = 4 Largemouth Bass caught). There was a significant positive linear relationship between fish length (mm) and age (y) in Largemouth Bass: age = 0.012 (length) (F1, 40 = 138, P < 0.001, r2 = 0.78; Fig. 6). Largemouth Bass average age was calculated as 2.0 y in 2012, 1.6 y in 2013, and 2.3 y i n 2014. Changes in limnological parameters following fish intr oduction Data from regular measurements in the 1970s show that the lake was acidic with pH ≈ 4.5 (Table 2; Rubin 1982). Between 1991 to 2013, pH increased more rapidly in Lake Minnewaska than the other acidified sky lakes on the Shawangunk Ridge and was closer to neutral at pH 6.1 in recent years (Table 2). This trend began before the fish were introduced, but pH has continued to increase following Figure 5. Histograms of N. crysoleucas (Golden Shiner) length in 2012 (n = 85) and 2013 (n = 361). No Golden Shiners were present in 2014. Northeastern Naturalist Vol. 22, No. 4 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 773 fish introduction. Lake Minnewaska underwent a recent increase in productivity and decrease in transparency following fish introduction (Table 2). Before fish introduction, the lake was oligotrophic with low TP and chl a concentrations and extremely high transparency (>6 m; Table 2). Following the Golden Shiner introduction, chl a and TP concentrations increased, transparency became much lower, and benthic anoxia was present in the hypolimnion; these facts all indicate the lake has transitioned to a mesotrophic condition (Table 2). Changes in variables relating Figure 6. Regressions of fish length (mm) and age (y) of N. crysoleucas (Golden Shiner, top) and M. salmoides (Largemouth Bass, bottom). Northeastern Naturalist 774 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 Vol. 22, No. 4 to lake productivity are associated with the introduction of fish, likely through a trophic cascade. Increases in TP may be due to greater internal cycling of nutrients in the lake (benthic-feeding fish excreting into the water column) or to the release of phosphorus from iron complexes in sediment under both neutral pH and anoxic conditions (Wetzel 2001). All data indicate that Lake Minnewaska has always had low specific conductivity (Table 2). Figure 7. Histograms of M. salmoides (Largemouth Bass) length in 2012 (n = 4), 2013 (n = 94), and 2014 (n = 108). Northeastern Naturalist Vol. 22, No. 4 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 775 Discussion The history of fish presence in Lake Minnewaska is linked to human activity. Fish were likely introduced in the 18th or 19th century and remained in the lake until pH decreased below a critical threshold for survival or reproduction. Lake Minnewaska pH has steadily increased over the past 40 years from pH = 4 in the 1970s to pH = 6.5 in 2014; we hypothesize this change is a result of recovery from acid rain, the loss of a large mat of Sphagnum trinitense Müller (Trinity Sphagnum) (van Breeman 1995), and addition of eroding, neutralizing shale from hiking trails that circumscribe the lake. Since 1999, the lake pH > 5.5 and could support acidtolerant fish (Kretser et al. 1989). A subset of Adirondack lakes with extirpated fish populations are also recovering from acidification. There has been a resurgence of acid-tolerant Brook Trout in Lake Honnedaga since 2000 (Josephson et al. 2014). Compared to Lake Minnewaska, the change in pH at Lake Honnedaga has been minimal, but the return of fish has been hastened by a tributary system that provided refugia for fish (Josephson et al. 2014). Lake Minnewaska’s single outlet stream is intermittent and has waterfalls impassable to fish, thus preventing dispersal of fish into the lake (D.M. Charifson, SUNY Stony Brook, NY, pers. comm.). Lake Minnewaska is one of 5 sky lakes on the Shawangunk Ridge, 4 of which were acidified and had a pH of 4–4.5 by the 1970s (Rubin 1982). Extirpation of fish in the Shawangunk Ridge occurred earlier than in the Adirondacks. Eighty percent (4/5) of lakes were fishless due to acidification by 1922, while only 4% of lakes in the Adirondack Mountains were fishless because of low pH by 1930; the percentage of acidic fishless lakes in the Adirondacks grew to 46% by the 1970s (Schofield 1976). We are less certain of the timing of fish loss in the other sky lakes. Fish were present in each lake in the late 19th century, but we must rely on historical accounts and anecdotal evidence (i.e., fish stories) to estimate past fish diversity. Table 2. Pre-fish (prior to 2009) and post-fish (2009 and later) means ± standard deviations of several key limnological variables. Chl a = chlorophyll a concentration and TP = total phosphorus concentration. T-test P-value indicates significant difference between pre- and post-fish values with associated degrees of freedom (df) for the heterogeneous variances comparison. Pre-fish Post-fish t-test Years with mean mean P-value df available data pH 5.2 ± 0.6 6.1 ± 0.3 less than 0.001 220 1970–2013 Secchi depth (m) 6.1 ± 1.8 2.9 ± 0.8 0.003 9 1989, 2000–2013 Chl a (μg/L) 0.9 ± 0.3A 4.4 ± 2.5 less than 0.001 41 1989, 1992, 2012–2013 TP (μg/L) 12.8 ± 3.5B 22.9 ± 14.6 less than 0.001 49 2004, 2009, 2011–2013 Specific conductivity (μS/cm) 50.7C 21.7 ± 11.7 NA NA 1972–1974, 2012–2013 Anoxia in hypolimnion NoD Yes - - 1992, 2000–2013 AFrom Baines and Pace (1994); Cole and Pace (1995). BNew York State Environmental Management Bureau, Albany, NY, unpubl. data; Cole et al. (1993). CRubin (1982), one value converted from 1972–1974 average in meq /L. DCole and Pace (1995); New York State Environmental Management Bureau, Albany, NY, unpubl. data. Northeastern Naturalist 776 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 Vol. 22, No. 4 Reliable historical records show that Yellow Perch and Chain Pickerel were present in another sky lake, Lake Awosting, prior to 1910 (Smiley and Huth 1983) but extensive fishing effort between 1915 and 1921 in Lake Awosting yielded no fish. Another sky lake, Lake Mohonk, was never acidified, has been stocked with game fish since 1871, and had pre-existing fish populations prior to stocking (Smiley and Huth 1983). The reintroduction of fish to Lake Minnewaska has caused numerous changes in whole-lake community structure. From 2010 to 2013, zooplanktivorous Golden Shiners likely suppressed zooplankton populations and contributed to internal loading of epilimnetic phosphorus. Both factors combined to result in increased phytoplankton biomass measured as pelagic chl a. Since the Golden Shiner has apparently been extirpated, the lake may see a decrease in producer biomass as zooplankton are released from predation. In fact, we saw transparency increase throughout the summer of 2014 to a maximum 6 m in early fall (D.C. Richardson et al., unpubl. data). Fishless lakes have rich and characteristic amphibian and macroinvertebrate communities and experience losses of these organisms with fish introductions (Bull and Marx 2002, Hecnar and M’Closkey 1997, Schilling et al. 2009). After fish introduction, Lake Minnewaska saw losses in amphibian-species richness and changes to macroinvertebrate-community composistion (Jorgensen 2012, L. Townley, New York State Environmental Management Bureau, Albany, NY, pers. comm.). The loss of the aquatic bryophyte, Trinity Sphagnum, appears to predate the fish introduction, but is likely linked to the changing pH. Temporal and spatial patterns of increased benthic coverage of Sphagnum spp. with decreasing pH have been observed in several acidified lakes in Sweden (Grahn 1977), so the converse could be true with Trinity Sphagnum greatly reduced or even extirpated by recovery from acidification in Lake Minnewaska. However, Sphagnum is an ecosystem engineer that acidifies its environment through production of organic acids; thus, we cannot rule out the possibility that recovery in Lake Minnewaksa was in part caused by the loss of Trinity Sphagnum (van Breeman 1995). We did not observe Golden Shiners in Lake Minnewaska in the summer of 2014 during electrofishing and diving surveys. This apparent extirpation likely occurred as a result of Largemouth Bass predation. Largemouth Bass increased in length by 56 mm between 2013 and 2014, resulting in larger fish with bigger gape sizes which enhanced their ability to consume larger Golden Shiners. The introduction or increased abundance of predatory fish can greatly reduce the populations of its prey species. When the Lake Trout population of Whitepine Lake began to increase due to increasing pH, the abundance of Yellow Perch decreased dramatically (Gunn and Keller 1990). Without the zooplanktivorous minnows, the lake will be trophically structured by piscivores like nearby Lake Mohonk, likely leading to changes in the zooplankton community via a trophic cascade (Carpenter et al. 1 987). The remaining fishless sky lakes are too acidic for most fish species. During summer the summer of 2013, the pH of each of the other 3 sky lakes was below 5.0 (D. Richardson et al., unpubl. data). As the remaining fishless sky lakes slowly recover from acidification, it may be possible for them to support fish. Northeastern Naturalist Vol. 22, No. 4 D.M. Charifson, P.C. Huth, J.E. Thompson, R.K. Angyal, M.J. Flaherty, and D.C. Richardson 2015 777 The pH of Lake Awosting has been slowly recovering over the past 22 years (J.E. Thompson et al., unpubl. data). If recovery in Lake Awosting continues linearly, the average pH will be 5.5 by ~2060, a pH suitable for survival of acid-tolerant fish species. However, fish will not be able to disperse into the lake without human aid due to geographic barriers. The reintroduction of fish to Lake Minnewaska can be viewed from multiple conservation perspectives. The lake is clearly on the road to recovery from anthropogenic acidification, although the introduction of fish has led to decreased abundance and extirpation of species with atypical behaviors that were only able to inhabit the lake in the absence of fish. For example, Bahret (1996) found that the Lake Minnewaska population of Eurycea bislineata Green (Northern Two-lined Salamander) exhibited no parental care of eggs and had a wide dispersal of eggs across habitats and depths—behaviors that have only been documented within Lake Minnewaska. The once crystal-clear waters had become green and opaque for several years, likely due to fish reintroduction, much to the dismay of visitors to Minnewaska State Park Preserve; however, we saw some recovery in transparency in 2014 following Golden Shiner loss. Little information is known about the state of the lake prior to acidification; however, a New York Times article indicated that the water was so clear that a white object could be seen ~9 m (30 feet) below the surface of Lake Minnewaska during the 1870s (NYT 1876). Management goals for Lake Minnewaska must be established in the context of what is known about its history and ecology. After further study of the ecosystem effects of the Largemouth Bass population, managers could begin a series of regular removals of fish by electrofishing to return the lake to a fishless state. Removal of fish may, to an extent, restore some of the uncommon community and ecosystem characteristics that existed historically, but successful fish reintroductions in the future remain a possibility due to increased pH. Acknowledgments This research was funded by grants and awards from the SUNY New Paltz Summer Undergraduate Research Experience program, SUNY New Paltz School of Science and Engineering, and the New York State Water Resources Institute to D.C. Richardson, J.E. Thompson, and Kathleen Weathers, and National Science Foundation Research Opportunity Award to D.C. Richardson as a supplement to NSF DEB #1144627 (Jon Cole, Principal Investigator). The Mohonk Preserve and NYS Environmental Management Bureau were crucial partners and contributed data and resources to this project. 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