Northeastern Naturalist 362 J.T. Stolarski 22001199 NORTHEASTERN NATURALIST 2V6(o2l). :2366,2 N–3o7. 82 Observations on the Growth, Condition, and Ecology of Lake Trout in Quabbin Reservoir, Massachusetts Jason T. Stolarski* Abstract – I report observations on the ecology and trends in growth and relative condition of Salvelinus namaycush (Lake Trout) in Quabbin Reservoir garnered from over 60 y of almost continuous monitoring. Fish were captured using gillnets during the spawn in late October and early November in 10–15 m of water. Spawning began when waters reached 17 °C, but activity was most intense between 11 °C and 13 °C. Spawning fish were 4–24 y old, and catches were typically comprised of 89.5% males. Male Lake Trout generally reached 457 mm (18 in; legal harvest size) by age 5, and since 2010, average growth of mature males was 5.8 mm per year. Length-at-capture and density have declined over the period of record but rose and fell over shorter intervals, likely in response to forage abundance, mainly Osmerus mordax (Rainbow Smelt). Introduction Salvelinus namaycush (Walbum) (Lake Trout) are widely distributed throughout their native range in northern North America, from the Alaskan peninsula east across Canada to Nova Scotia and south to northern New York (Scott and Crossman 1973). These fish predominate in deep, cold-water lakes, where their life-history is typified by slow growth, longevity, and large body size (Gunn and Pitblado 2001). Despite slow growth rates, the potential for large body size makes Lake Trout particularly attractive as a sport fish and is likely one of the reasons they have been introduced extensively outside their native range (Crossman 1995). In Massachusetts, Lake Trout were first stocked unsuccessfully in the late 1800s and only became established in the state following the creation of Wachusett and Quabbin Reservoirs in the first half of the 20 th century (Cardoza 2015, Hartel et al. 2002). Quabbin Reservoir is a 99.4-km2 impoundment of the Swift River, located in central Massachusetts, and is the largest waterbody in the Commonwealth by surface area and volume. Built to supply potable water to the city of Boston and surrounding communities, construction finished in 1939, and the reservoir reached full pool in 1946, at which point fishing was opened to the public. Lake Trout were first stocked in the Quabbin Reservoir in 1952 with an initial introduction of 10,000 Lake Trout fingerlings acquired from an undocumented source in Vermont (Cardoza 2015). Additional introductions of fry originating from the Lake Ontario region of New York occurred annually between 1953 and 1958 (Cardoza 2015, Hartel et al. 2002). Further releases of fry in 1963 and 1964 came from the Finger Lakes region of New York which, at the time, were described as a deep-spawning strain 1Massachusetts Division of Fisheries and Wildlife, Field Headquarters, 1 Rabbit Hill Road, Westborough, MA 01581. *Corresponding author - Jason.Stolarski@mass.gov. Manuscript Editor: John Waldman Northeastern Naturalist Vol. 26, No. 2 J.T. Stolarski 2019 363 (Hartel et al. 2002). During the initial Lake Trout introductions, Osmerus mordax (Mitchill) (Rainbow Smelt) roe were salvaged from inland and coastal streams in Massachusetts and distributed in Quabbin tributaries in an effort to supplement the forage base of the reservoir. Lake Trout were first caught by anglers in 1956 and since then have been arguably one of the most popular sport fisheries in the Commonwealth (Cardoza 2015). Monitoring of the Lake Trout population in Quabbin Reservoir began in 1956, and by 1970, Bridges and Hambly (1971) noted considerable variability in annual estimates of growth, condition, and harvest. Similar variability has been observed in Lake Trout populations throughout their range and has been attributed in part to food-web structure and abundance and distribution of forage fish (Hammers 2018; Hassinger and Close 1984; Martin 1966, 1970; Pazzia et. al. 2002; Rupp 1968). Bridges and Hambly (1971) concluded that changes in forage-fish abundance, primarily Rainbow Smelt, were likely key to Lake Trout growth and success, noting that individuals reached 457 mm (18 in; minimum legal size) a full year earlier during periods of Rainbow Smelt abundance. Since that time, changes in reservoir productivity brought about via natural aging, climate change, and acidification have all likely altered the biotic and abiotic environments of the reservoir (USEPA 2016, Wetzel 1975). As such, and in light of additional Lake Trout data, an updated analysis of Lake Trout dynamics was warranted. The purpose of this research was to investigate long-term trends in Lake Trout length and relative condition and, where possible, relations between these indices and populations of forage fish in Quabbin Reservoir. I also report on aspects of the ecology of Quabbin Reservoir Lake Trout gleaned from close to 60 y of nearly continuous monitoring of one of the southern-most self-sustaining Lake Trout populations in the northeastern US. Field Site Description Quabbin Reservoir is a 99.4-km2 reservoir located in central Massachusetts. The reservoir is characterized by 2 main longitudinal sections that are linked by a channel. Each section terminates at a water-control structure—Windsor dam to the west, and Goodnough Dike to the east (Fig. 1). Major inflows include the East, Middle, and West branches of the Swift River and seasonal transfers from the Ware River. Water resides in the reservoir an average of 4 y and at full pool, Quabbin Reservoir contains ~1.56 billion m3 of water with an average depth of 13.7 m and a maximum depth of 46 m (MADCR 2007). The reservoir is oligotrophic and dimictic, and all of its waters retain dissolved oxygen (DO) concentrations exceeding 5 mg/L year-round. The Quabbin watershed encompasses 484 km2, of which 87% is forested and 74% is protected from development in some fashion. The dominant forest cover is Quercus spp. (oaks) intermixed with Acer rubrum L. (Red Maple) in wetter soils, and Pinus spp. (pines) in drier soils (MADCR 2007). Due to the level of protection afforded to lands within the Quabbin Reservoir watershed since the inception of the reservoir, these areas are considered some of the most pristine in the Commonwealth. Northeastern Naturalist 364 J.T. Stolarski 2019 Vol. 26, No. 2 Methods Fish sampling Researchers primarily collected Lake Trout via sinking gillnets set at night on known spawning locations on Windsor Dam and Goodnough Dike from late Octo - ber to early November. Sampling during the spawn leverages Lake Trout spawning aggregations to maximize catch rates but precludes the capture of immature fish and ultimately restricts findings and implications to fish of reproductive age. Sampling efforts commenced in 1956 and extended continuously until 1979, after which time sampling resumed in 1993 and has continued almost annually since. Gill nets were 1.8 m (6 ft) high, varied in size between 45.7 m (150 ft) and 91.4 m (300 ft) long, and prior to 1993, consisted of 25.4-mm (1-in) square mesh. After 1993, multi-panel experimental gill nets had 38.1-mm (1.5-in) square mesh transitioning to 88.9- mm (3.5-in) square mesh. Approaching sundown, crews of 2–5 people in a boat set Figure 1. Map of Quabbin Reservoir showing the main tributaries, Lake Trout spawning and sampling locations on Windsor dam and Goodnough Dike, and an inset showing the relative position of the reservoir within Massachusetts. Northeastern Naturalist Vol. 26, No. 2 J.T. Stolarski 2019 365 nets perpendicular to the dam face. Typically the inshore lead was set within 5 m of shore, with the offshore end typically resting in 15–18 m of water. Nets were fished for 30 min to 1 h, depending upon fish activity. Short net-sets minimized stress and mortality of captured fish. Upon retrieval, researchers carefully removed fish from the nets and placed in an onboard live well. Each fish was weighed to the nearest gram (beginning in 1974), measured to the nearest mm total length, and sexed by the presence of reproductive products or via external characteristics. Fish were then implanted with a uniquely numbered tag. Prior to 2006, T-bar anchor tags were inserted behind pterygiophore bone structures in the dorsal musculature posterior to the dorsal fin. Starting in 2006, fish were implanted with a uniquely numbered full duplex passive integrated transponder (PIT) tag inserted underneath the skin in the pelvic girdle. Following tagging, fish were released away from the point of capture to minimize recapture later in the evening. Any accidental mortalities were retained for aging purposes. Between 1956 and 1970, Rainbow Smelt abundances were qualitatively determined via gut-content analyses (Bridges and Hambily 1971). Researchers captured Lake Trout via angling and gill net throughout the reservoir during spring and summer and excised their stomachs. Food items were classified to the lowest taxonomic level possible and tallied. Since 2008, forage-fish counts have been garnered from weekly cleanings of protective screens covering the Quabbin Reservoir intake shafts located on Windsor Dam. Fish caught on the screens are identified to species, enumerated, and summed across years. Environmental data The Massachusetts Department of Conservation and Recreation, Division of Water Supply Protection (DWSP) provided August water temperature and DO profile data from 1990 to 2017. Water quality profiles were typically performed during the second week of the month, weather permitting, during the open-water season at a fixed position located near the face of Windsor Dam. I used August profile data to estimate potential Lake Trout habitat by determining the minimum and maximum elevations that were <15 °C and contained >6 mg/L DO, then converted the area to volume using a digital elevation model in ArcGIS (Plumb and Blanchfield 2011). For each profile, I identified the thermocline as the depth where the rate of change in temperature was highest and calculated mean hypolimnetic temperature using all temperature data below that point. I obtained continuous water temperatures measured at the reservoir intake shaft from Massachusetts Water Resources Authority (MWRA) databases, from which I derived daily means from the period 1 January 2005 to 31 December 2017. Fish aging Beginning in 2014, I extracted sagital otoliths from accidental gill net mortalities using the “open the hatch” method of Secor et al. (1992), then rinsed, dried, and and stored them in individually labeled scale envelopes. In the laboratory, I prepared a sagittal otolith of each fish by affixing it to a glass slide using Crystalbond ® thermoplastic cement perpendicular to the long axis of the otolith, grinding Northeastern Naturalist 366 J.T. Stolarski 2019 Vol. 26, No. 2 each otolith to the core in the transverse plane using a thin section machine (Hillquist Inc., Denver, CO), remounting to the slide’s flat side before grinding to a final thickness of ~0.2 mm, and hand polishing with a 1-μm diamond abrasive. Using a compound microscope, I viewed otoliths at 20x and 40x magnifications under transmitted light. If, after inspection, I deemed the mounted otolith section inadequate for age determination, the second sagittae was processed in the same fashion. I made age determinations by enumerating opaque zones (Beamish 1979). Statistics I calculated the relative condition of Lake Trout as: Kn = (W/W') * 100, where W is individual length and W' is the predicted length-specific weight enumerated from a linear regression of log-transformed weight–length data from the population (LeCren 1951). Annual absolute growth rate was calculated for recaptured fish as: ([Lt2 - Lt1] / [t2 - t1]) * 365, where L is length at capture (t1) and recapture (t2) measured in days (Busacker et al. 1990). I fit age and length data with a Von Bertalanffy growth model as: Lt = L∞ (1 - e-K( t - t0)), where Lt is length at time t, L∞ is asymptotic length, K is the growth coefficient, and t0 is a theoretical time where length would be 0. I employed maximum likelihood to iteratively estimate all parameters in the model in the nls package of the statistical software R (Isely and Grabowski 2007, R development Core Team 2017). I used Pearson’s product moment correlation to compute correlations among Lake Trout statistics (relative condition and length at capture), habitat (mean hypolimnetic temperature and habitat volume), and forage-fish metrics, and tested significance with a t-test at α = 0.05. I conducted a generalized linear regression to model nightly Lake Trout catch as a function of water temperature (Poisson family) and female proportion as a function of sample date (binomial family) pooled across years. Results Although Lake Trout sampling efforts began in 1956, raw data collected between 1956 and 1963 were lost but are reported in Bridges and Hambly (1971). Since 1964, a total of 6691 Lake Trout have been sampled, of which 4723 were tagged, and 331 have been recaptured. The majority of Lake Trout (n = 3308) were tagged on spawning grounds at Windsor Dam, with an additional 1183 tagged on spawning grounds at Goodnough Dike. Of these fish, a total of 19 or 2.6% were recaptured in an area different from where they were tagged, which is likely an Northeastern Naturalist Vol. 26, No. 2 J.T. Stolarski 2019 367 underestimate of the percentage of fish that move between spawning grounds, as tag releases and sample effort at each location were not consistent over time. The average time between capture and recapture was 2.25 y; the longest time between capture was 21 y for a fish tagged in 1996 and recaptured for the first time in 2017. Only 7% of recaptured fish have been recaptured more than once; the maximum number was 5 captures for a single fish between the years 1965 a nd 1975. Catch rates of spawning Lake Trout intensify shortly after sunset, when fish are active. The majority of fish were captured at water depths of 10–15 m. Spawning may take place in deeper water; however, these habitats were not sampled extensively. Individuals were captured in water temperatures varying from 11 °C to 17 °C, with the majority of fish captured between 11 °C and 13 °C (Fig. 2). Spawning fish were 4–24 y of age, with individuals 500–600 mm in length displaying considerable variability in age (Fig. 3). Von Bertalanffy growth-model results suggest individuals reached 457 mm (18 in; legal harvest size) in length by age 5; however, limited numbers of fish near this size were included in the dataset. Male Lake Trout comprised an average 89.5% of the catch in a given year and outnumbered females in every year. As a result, analysis regarding length-at-catch, growth, and relative condition has been restricted to male fish. The percentage of females in the catch declined significantly (z =-6.43, P < 0.05) over the spawning period from late October to early November (Fig. 4). Lake Trout length-at-capture was not significantly correlated to habitat volume (ρ = -0.080, t = -0.350, P = 0.730 or mean hypolimnetic temperature (ρ = -0.159, Figure 2. Nightly catch of Lake Trout vs. temperature (°C) for fish caught on Windsor Dam and Goodnough Dike during October and November from 2006 to 201 7. Northeastern Naturalist 368 J.T. Stolarski 2019 Vol. 26, No. 2 t = -0.706, P = 0.488), nor was Lake Trout relative condition significantly correlated to habitat volume (ρ = 0.059, t = 0.259, P = 0.798) or mean hypolimnetic temperature (ρ = 0.044, t = 0.195, P = 0.847). Furthermore, slopes of linear trend lines fitted to Lake Trout habitat volume and mean hypolimnetic temperature over time were not significantly different from zero (Fig. 5). Median growth-rate estimates from fish recaptured between 1964 and 2017 were highest during the 1970s, at 17.3 mm/y (Fig. 6). Beginning in 2000, growth increased slightly from 7 mm/y to 8.7 mm/y, but since 2010, the median growth rate of mature male fish has been 5.9 mm/y or 1.3% of body length annually (Fig. 6). Growth estimates could not be calculated for the 1980s because too few fish were recaptured and 39, or roughly 11% of all recaptured fish exhibited negative growth rates. Investigating finer-scale patterns from tag-return data was hampered by low sample sizes and difficulty assigning growth to a particular year when fish were often recaptured after being at large for multiple years. Overall, mean length at catch for male Lake Trout has declined since its peak in 1964 (Fig. 7). Embedded within the long-term trend are shorter (sub-decadal) oscillations in length at capture, most recently peaking in 2010. The forage-fish count increased by a factor of 10 in 2009, mirroring the increase in length-at-capture. However, length-at-capture and counts of forage fish do not display a significant correlation (ρ = 0.595, t = 1.961, P = 0.091) over the entire period where data are Figure 3. Lake Trout length as a function of age determined from otoliths for 66 fish captured from Quabbin Reservoir between 2014 and 2017 fitted with a Von Bertalanffy growth function (solid line) with growth coefficient (K) and maximum th eoretical size (Linf). Northeastern Naturalist Vol. 26, No. 2 J.T. Stolarski 2019 369 concurrent. Lake Trout relative condition has also declined since 1974; the year that weights were first recorded during sampling (Fig. 8). Sub-decadal cycles are also apparent, most notably between 2006 and 2013. when Lake Trout relative condition reached near-record highs and lows over a relatively short time period. Again, this period coincided with the large increase observed in counts of forage fish in 2009. However, relative condition and counts of forage fish did not display a significant correlation (ρ = 0.305, t = 0.847, P = 0.425) over the entire period where data are concurrent. Lake Trout relative condition and to a lesser extent length at capture have increased in recent years (Figs. 7, 8). Discussion Two large spawning areas are present at Windsor Dam and Goodnough Dike, although it is probable that Lake Trout spawn throughout the reservoir. These areas are likely attractive spawning locations due to the abundance of broken rocks armoring the face of the structures and prevailing winds that are perpendicular to their faces. Wind agitates the water and removes fine sediments from interstitial spaces of the coarse sediments. These spaces protect eggs from predation (Sly and Evans 1996). The spawning period between late October and early November corresponds to that of populations in adjacent states but is slightly later in the year Figure 4. Female percentage with standard errors as a function of sample date (mm-dd) for Lake Trout captured from Quabbin Reservoir collected between 1964 and 2017. Northeastern Naturalist 370 J.T. Stolarski 2019 Vol. 26, No. 2 relative to populations in northern Maine (Johnson 2001; J. Kratzer, Vermont Fish and Wildlife Department, St. Johnsbury, VT, pers. comm.; Overlock 2016; Royce 1943; J. Viar, New Hampshire Fish and Game Department, New Hampton, NH, pers. comm.). Water temperatures during peak catches (11–13 °C), which are potentially indicative of heightened spawning activity, are slightly greater than spawning temperatures observed in New Hampshire populations (9–11 °C ) but are consistent with populations elsewhere (Scott and Crossman 1973; Sly and Evans 1996; J. Viar, pers. comm.). Male fish comprised an average of 89.5% of the fish sampled in any 1 year, which is consistent with rates obtained from fall sampling in lakes in New Hampshire (J. Viar, pers. comm.). The predominance of male fish is likely a result of differences in spawning behaviors and activity between male and female fish. Male fish are known to precede females at the spawning grounds and prepare spawning habitats by sweeping away debris (Hartel et al. 2002, Sly and Evans 1996). These and other antagonistic behaviors might increase the susceptibility of male fish to passive sampling gear such as gillnets. However, skewed sex ratios could also be a natural component of the population or result from a greater prevalence of nonconsecutive– year spawning in females (Hartel et al. 2002, Royce 1943, Scott and Crossman 1973). The decline in the percentage of females caught as the spawning Figure 5. (A) Potential Lake Trout habitat volume in millions of cubic meters and (B) mean hypolimnetic temperature in Celcius calculated from August water-quality profiles collected between1990 and 2017 in Quabbin Reservoir. Northeastern Naturalist Vol. 26, No. 2 J.T. Stolarski 2019 371 season progressed mirrors similar trends observed in Lake Trout populations elsewhere (MacLean et al. 1981, Sly and Evans 1996). Quabbin Lake Trout retained for aging since 2014 were found to attain 457 mm (18 in, legal size) in length by age 5. However, the sample used for aging purposes contained few fish under 7 y or over 15 y of age and was confined to a very narrow range of lengths. As a result, this statistic as well as Von Bertalanffy growth parameters should be considered estimates that will improve with the addition of samples outside the afore-mentioned range. Bridges and Hambly (1971) noted that, during periods of elevated Rainbow Smelt abundance, Quabbin Reservoir Lake Trout reached legal size at age 4 as opposed to age 5 when Rainbow Smelt were less abundant. Variability in Lake Trout size at age is quite common throughout their range and might be a function of variability in food-web structure (Pazzia et al 2002). In the Northeast, Lake Trout from Keuka Lake, in western New York, were found to reach 457 mm between the ages of 5 y and 7 y, depending upon lake productivity and abundance of forage fish (Hammers 2018), while populations in Vermont usually reached this size by age 6 (J. Kratzer, unpubl. data). Lake Trout in New Hampshire reached 457 mm between the ages of 6 y and 8 y (J. Viar, pers. comm.), while farther south in 2 Tennessee Lakes, Lake Trout reached this size by age 3 y (Russell and Bettoli 2013). Maine populations have been observed to reach Figure 6. Median Lake Trout annual growth rate calculated from 331 recaptured mature male fish pooled by decade showing interquartile range and sample sizes with the number of individuals displaying negative growth in parenthesis. Estimations of annual growth during 1980 were not possible due to insufficient tag returns during th at time Northeastern Naturalist 372 J.T. Stolarski 2019 Vol. 26, No. 2 457 mm between the ages of 5 y and 7 y (Johnson 2001), and in Follensbury Pond, located in the Adirondacks, NY, by age 11 y (Lenker et al. 2016). Since 2010, the median growth rate of mature male Lake Trout at Quabin Reservoir has been 5.9 mm/y, with 10% of the recaptured fish exhibiting negative growth. The average time these fish were at large was 2 y; thus negative growth estimates could be explained by measurement error of a very slow-growing fish species. However, negative growth rates have been documented in a population of Lake Trout in Moosehorn Lake, ME (Auclair 1982). Trends in pooled growth estimates from tag returns are unclear and do not match trends seen in length-at-catch and relativecondition data. However, this finding may not be surprising given the inconsistent number of returns over time, which necessitated pooling returns across decades. Long-term declining trends in length-at-capture and relative condition are likely a result of multiple factors. Greater length-at-capture observed in the first 10–15 years following the establishment of a reproducing population is probably due to Figure 7. Mean size-at-catch (solid points) organized by year, with 95% confidence intervals and sample sizes for spawning male Lake Trout captured from Quabbin Reservoir between 1964 and 2017; please note x-axis break. Solid vertical lines at top of figure refer to and demarcate periods of smelt abundance (Decr. = decreasing, Abs. = absent, and Incr. = increasing smelt abundance; also long period with no available data is noted), which was determined from diet samples and recreated from Bridges and Hambly (1971). Dashed line and open points on secondary y-axis are counts of forage fish garnered from Quabbin intake screens between 2008 and 2017; these counts were not significantly correlated to length-atcapture over same time interval (ρ = 0.595; t = 1.961; P = 0.091). Northeastern Naturalist Vol. 26, No. 2 J.T. Stolarski 2019 373 low initial Lake Trout densities and reduced competition for resources. In contrast, decreases in length at capture and relative condition observed since establishment could indicate that Lake Trout densities have increased. Corresponding data regarding abundance or relative abundance would provide additional insight, but data loss and aspects of the study design and ecology of Lake Trout prevented me from calculating abundance estimates. My calculation of catch-per-unit effort was hampered by the loss of or failure to consistently retain gill-net soak times over the many years of monitoring. Furthermore, increased catch on any particular night may be more of a function of water temperature and heightened spawning activity than of actual changes in abundance. I was also unable to make population estimates via mark–recapture data because these metrics assume equal catchability. Capture probabilities are likely to be heterogeneous because Lake Trout exhibit some degree of spawning-site fidelity, sampling locations target mature fish exclusively, and male fish, probably due to greater activity, are more likely to be captured relative to females (Binder et al. 2016, Sly and Evans 1996). Although sampling during the spawn imposes certain limits on data interoperability, similar efforts Figure 8. Mean relative condition of spawning male Lake Trout (solid points, primary yaxis) with 95% confidence intervals and forage-fish counts (open points and dashed line, secondary y-axis) as a function of year for Quabbin Reservoir between 1974 and 2017; please note x-axis break. Pearson’s correlation coefficient (ρ), t-value (t), and P-value (P) pertain to correlation of Lake Trout relative condition and forage-fish abundance between 2008 and 2017. Northeastern Naturalist 374 J.T. Stolarski 2019 Vol. 26, No. 2 conducted outside of the spawn when fish were dispersed have resulted in extremely low sample sizes. Similarly, shifts in the age structure of the population towards younger and smaller fish could also be responsible for the decline in length-at-capture and relative condition over time. The limited numbers of fish retained for aging purposes varied in age from 4 y to 24 y of age, with 75% of the observations falling between 7 y and 12 y. Lake Trout were introduced beginning in 1952 and the year lengthat- capture was highest in 1964, when the oldest fish at that time could not have exceeded 12 y of age. Given the popularity of the fishery and harvest levels in the preceding years, it is likely that the age structure was skewed toward younger age classes during the early 1960s relative to the present (Bridges and Hambly 1971). However, little additional age distribution data exists to compare to current age distributions. Researchers at the Quabbin Reservoir will continue to age incidental mortalities with the goal of detecting any future changes to the age distribution of the population. Changes in abiotic factors, such as water temperature, dissolved oxygen, and nutrients could also contribute to changes in Lake Trout length-at-catch and relative condition. King et al. (1999) noted poorer Lake Trout growth in years with earlier stratification that likely limited habitat. The amount of habitat available to Lake Trout and the mean temperature of the hypolimnion have shown variability since 1990, but there is no significant trend overall (Fig. 5). However, the data do not encompass the entire period of record of Lake Trout sampling. Reservoir productivity was likely higher in the 1950s and 1960s because large quantities of allochthonous material were inundated and metabolized as the reservoir filled (Wetzel 1975). Within Quabbin, the oxygen content of bottom waters approached zero during summer of the first 3 y of the impoundment, which indicates that productivity was higher in the past (Bridges and Hambly 1971). Greater productivity during this time likely contributed to greater Lake Trout growth. Shorter-term or subdecadal trends in Lake Trout length-at-capture show some agreement with qualitative smelt data gathered by Bridges and Hambly (1971) in the 1960s, although the relationship could not be tested empirically. Lake Trout exhibited a large drop in length-at-capture between 1964 and 1967, corresponding to a smelt-control program implemented over roughly the same time period (Fig. 7). The control program was initiated by the Metropolitan District Commission in 1959 in response to super-abundant Rainbow Smelt populations that began to clog the gravity-fed distribution intakes, which resulted in a system-wide loss of pressure and endangered the water supply to millions of people. By 1964, Rainbow Smelt populations were substantially depressed but efforts to control them continued until 1968, when protective screens were installed at the intakes. Shortly after, Rainbow Smelt were again stocked but lenght at capture and relative condition of Lake Trout did not recover until the early 1970s (Fig. 7; Bridges and Hamb ly 1971). Between 2008 and 2010, counts of forage fish (primarily Rainbow Smelt) rose and subsequently fell by more than a factor of 10. Shortly after, between 2011 and 2013, Lake Trout length-at-capture and relative condition declined substantially. Northeastern Naturalist Vol. 26, No. 2 J.T. Stolarski 2019 375 However, the correlation between these metrics was not significant over the entire period when data were concurrent. Forage-fish count data garnered from intake screens are not ideal because they are only 1 measurement collected at a small, fixed location. Relative to modern methods used to estimate abundances of forage fish, such as hydroacustics, these data likely provide only a coarse estimate. Given this uncertainty, it might not be surprising that Lake Trout length-at-capture and relative condition corresponded to counts of forage fish only during periods of dramatic change such as occurred in the 1960s and again between 2008 and 2010. While these analyses do not show a statistically significant correlation between Rainbow Smelt populations and Lake Trout length-at-capture and relative condition, correspondence between these metrics during periods of large change provide evidence that such a relationship exists, as it does in Lake Trout populations elsewhere (Hammers 2018; Hassinger and Close 1984; Martin 1966, 1970; Rupp 1968). The collection of estimates of abundance of forage fish abundance that are more precise via hydroacustics would provide finer detail regarding the relationship between the abundance of forage fish and the length and relative condition of Lake Trout in Quabbin Reservoir. Rainbow Smelt populations are known to undergo large and rapid changes in abundance from year to year (Brown 1994, Rupp 1968). Cycles in abundance have been theorized to result from predation, temporal mismatches in forage abundance, and/or effects of water quality (McCullough and Stanley 1979, O’Brien et al. 2012, Rupp 1968). Individuals are known to spawn in tributary streams but also in shoal environments. Keller (1987) noted several instances of reproductive failure in streams most likely resulting from episodic depressions in stream pH due to hydrogen ion loading within the watershed (Keller and Easte 1989, Kostecki et al. 1985, USEPA 2016). Such conditions may have shifted reproductive output to shoal habitats within the Quabbin Reservoir (Keller 1987). Although little is known regarding the efficacy of Rainbow Smelt reproduction in shoal vs. stream habitats, diversifying egg deposition amongst 2 different habitat types certainly affords insurance against recruitment failure resulting from differential environmental conditions among habitat types in any given year. Reliance upon a single spawning habitat would likely reinforce or even amplify boom and bust cycles should the conditions be unfavorable for recruitiment of Lake Trout in one relative to the other of the habitat types from year to year. However, the effects of these cycles on Lake Trout growth and relative condition may be mediated by alternative forage species such as Morone americana (Gmelin) (White Perch) and invertebrates. In fact, during periods of limited abundance of forage fish, the incidence of Asellus spp. (isopods) in the stomach contents of Lake Trout has been observed to increase (Hammers 2018; J.T. Stolarski, unpubl. data). Since their introduction, Lake Trout in Quabbin Reservoir have arguably been one of the most popular game fish in Massachusetts. Populations have been monitored almost continuously since 1952 and have, over that time, shown decreases in length-at-capture and relative condition. Greater initial lengths and to a lesser extent, condition factors are likely a result of low initial Lake Trout densities and, Northeastern Naturalist 376 J.T. Stolarski 2019 Vol. 26, No. 2 thus, reduced competition, a young and productive reservoir, and a recently introduced and expanding forage base. Since then, populations have likely come to equilibrium as increased Lake Trout densities and lower reservoir productivity have limited Lake Trout growth. Shorter-term changes in these metrics might be a result of Lake Trout capitalizing on, or suffering from increases or decreases in forage fish (primarily Rainbow Smelt) over similar time intervals. Future work to investigate trends in forage-fish abundance and reproductive strategies may help elucidate biotic and abiotic controls on abundance and the relative contribution and efficacy of stream and shoal-spawning behaviors. Such information may help resource professionals proactively manage Lake Trout and other sportfish in Quabbin Reservoir and other waterbodies in New England now and in the future. Acknowledgments I thank the numerous biologists, technicians, and volunteers who have worked on this project since its inception, particularly Leanda Fontaine-Gagnon and past supervisors Bill Tompkins, Louis Hambly, Robert McCaig, Joseph Bergin, and Todd Richards. Thanks also to Brett Boisjolie and Max Nyquist, who provided water quality data from the databases of DWSP and MWRA and both the internal and anonymous reviewers of earlier versions of the manuscript, whose comments improved it considerably. Literature Cited AuClair, R.P. 1982. Moosehead Lake fishery management. Maine Department of Inland Fisheries and Wildlife, Research Bulletin 11, Augusta, ME. 175 pp. Beamish, R.J. 1979. Differences in the age of Pacific Hake (Merluccius productus) using whole otoliths and sections of otoliths. Journal of the Fisheries Research Board of Canada 36:141–151. Binder, T.R., S.C. Riley, C.M. Holbrook, M.J. Hansen, R.A. Bergstedt, C.R. Bronte, J.X. He, and C.C. Krueger. 2016. Spawning-site fidelity of wild and hatchery Lake Trout (Salvelinus namaycush) in northern Lake Huron. Canadian Journal of Fisheries and Aquatic Sciences 73(1):18–34. Bridges, C.H., and L.S. Hambly. 1971. A summary of eighteen years of salmonid management at Quabbin Reservoir, Massachusetts. American Fisheries Society Special Publication 8:243–259. Brown, R.W. 1994. Reproduction, early life history, and recruitment of Rainbow Smelt in St. Martin Bay, Lake Huron. Ph.D. Dissertation. Michigan State University, East Lansing, MI. Busacker, G.P., I.R. Adelman, and E.M. Goolish. 1990. Growth. Pp. 363–387, In C.B. Schrek and P.B. Moyle (Eds.). Methods for Fish Biology. American Fisheries Society, Bethesda, MD. 684 pp. Cardoza, J.E. 2015. The Massachusetts Division of Fisheries and Wildlife: 1866–2012. Massachusetts Division of Fisheries and Wildlife, Westborough, MA. 333 pp. Crossman, E.J. 1995. Introduction of Lake Trout (Salvelinus namaycush) in areas outside its native distribution: A review. Journal of Great Lakes Research 21:17–29. Gunn, J.M., and R. Pitblado. 2004. Lake Trout, the Boreal Shield, and the factors that shape Lake Trout ecosystems. Pp. 3–18, In J.M. Gunn, R.J. Steedman, and R.A. Ryder (Eds.). Boreal Shieldwaters: Lake Trout Ecosystems in a Changing Environment. Lewis Publishers, CRC Press, Boca Raton, FL. 528 pp. Northeastern Naturalist Vol. 26, No. 2 J.T. Stolarski 2019 377 Hammers, B.E. 2018. Keuka Lake salmonine management assessment, 2010–2016 update. New York State Department of Environmental Conservation, Federal Aid in Sportfish Restoration, Project F–53–R, Avon, NY. 48 pp. Hartel, K.E., D.B. Halliwell, and A.E. Turner. 2002. Inland Fishes of Massachusetts. Massachusetts Audobon Society. Lincoln, MA. 328 pp. Hassinger, R.L., and T.L. Close. 1984. Interaction of Lake Trout and Rainbow Smelt in two northeastern Minnesota lakes. Minnesota Department of Natural Resources, Section of Fisheries Investigational Report 379, St. Paul, MN. Isely, J.J., and T.B. Grabowski. 2007. Age and growth. Pp. 187–228, In C.S. Guy and M.L. Brown (Eds.). Analysis and Interpretation of Freshwater Fisheries Data. American Fisheries Society, Bethesda, MD. 961 pp. Johnson, P. 2001. Lake Trout management plan. Maine Department of Inland Fisheries and Wildlife, Division of Fisheries and Hatcheries, Greeneville, ME. 38 pp. Keller, R.L. 1987. Acidification and fish harvest trends at Quabbin Reservoir. Massachusetts Division of Fisheries and Wildlife, Publication 15010-62-200-9-87-CR, Westborough, MA. 52 pp. Keller, R.L., and W.E. Easte. 1989. Mitigating metal-induced Smelt egg (Osmerus mordax) mortality in Quabbin Reservoir tributaries using polypropylene screening as an artificial spawning substrate to transplant eggs to the relatively metal-free environment of the reservoir. Massachusetts Division of Fisheries and Wildlife, Technical Report, Westborough, MA. 39 pp. King, J.R., B.J. Shutter, and A.P. Zimmerman. 1999. Empirical links between thermal habitat, fish growth, and climate change. Transactions of the American Fisheries Society 128:656–665. Kostecki, P.T., K.R. Byrne, and E.J. Calabrese. 1985. Reproductive failure due to environmental pH and ionic factors in landlocked Rainbow Smelt (Osmerus mordax). University of Massachusetts Water Resources Research Center Technical Report, Amherst, MA. 42 pp. Le Cren, E.D. 1951. The length–weight relationship and seasonal cycle in gonad weight and condition in the perch (Perca fluviatilis). Journal of Animal Ecology 20:201–219. Lenker, M.A., B.C. Weidel, O.P. Jensen, and C.T. Solomon. 2016. Developing recreational harvest regulations for an unexploited Lake Trout population. North American Journal of Fisheries Management 36:385–397. MacLean, J.A., D.O. Evans, N.V. Martin, and R.L. DesJardine. 1981. Survival, growth, spawning distribution, and movements of introduced and native Lake Trout (Salvelinus namaycush) in two inland Ontario lakes. Canadian Journal of Fisheries and Aquatic Sciences 38:1685–1700. Martin, N.V. 1966. The significance of food habits in the biology, exploitation, and management of Algonquin Park, Ontario, Lake Trout. Transactions of the American Fisheries Society 95:415–422. Martin, N.V. 1970. Long–term effects of diet on the biology of the Lake Trout and the fishery in Lake Opeongo, Ontario. Journal of the Fisheries Research Board of Canada 27:125–146. Massachusetts Department of Conservation and Recreation (MADCR). 2007. Quabbin Reservoir Watershed System: Land Management Plan 2007–2017. Massachusetts Department of Conservation and Recreation, Division of Water Supply Protection, Boston, MA. 351 pp. McCaig, R.S., and J.W. Mullan. 1960. Growth of eight species of fishes in Quabbin Reservoir, Massachusetts in relation to age of reservoir and introduction of smelt. Transactions of the American Fisheries Society 89:27–31. Northeastern Naturalist 378 J.T. Stolarski 2019 Vol. 26, No. 2 McCullough, R.D., and J.G. Stanley. 1981. Feeding nich dimensions in larval Rainbow Smelt (Osmerus mordax). International Council for the Exploration of the Sea, ICES/ ELH FM 4, Copenhagen, Denmark. O’Brien, T.P., W.W. Taylor, A.S. Briggs, and E.F. Roseman. 2012. Influence of water temperature on Rainbow Smelt spawning and early life-history dynamics in St. Martin Bay, Lake Huron. Journal of Great Lakes Research 38(4):776–785. Orlock, J.R. 2016. Determining Lake Trout spawning area at Tunk Lake. Maine Department of Inland Fisheries and Wildlife. Fishery Interim Summary Report No. 16–4, Job F–011, Augusta, ME. 16 pp. Available online at https://www.maine.gov/ifw/docs/fisheriesreports/ 2016/tunklake.pdf. Pazzia, I., M. Trudel, M. Ridgeway, and J.B. Rasmussen. 2002. Influence of food-web structure on the growth and bioenergetics of Lake Trout (Salvelinus namaycush). Canadian Journal of Fisheries and Aquatic Sciences 59:1593–1605. Plumb, J.M., and P.J. Blanchfield. 2009. Performance of temperature and dissolved oxygen criteria to predict habitat use by Lake Trout (Salvelinus namaycush). Canadian Journal of Fisheries and Aquatic Sciences 66:2011–2023. R Core Team. 2017. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. Available online at https://www.R–project. org/. Accessed March 2017. Royce, W.F. 1943. The reproduction and studies on the life history of the Lake Trout, Cristivomer namaycush namaycush (Walbaum). Ph.D. Dissertation. Cornell University. Ithaca, NY. Rupp, R.S.1968. Life history and ecology of the smelt (Osmerus mordax) in inland waters of Maine. Maine Department of Inland Fisheries and Game, Final Report F–10–R, Augusta, ME. 36 pp. Russell, D., and P.W. Bettoli. 2013. Population attributes of Lake Trout in Tennessee Reservoirs. Southeastern Naturalist 12:217–232. Scott, W.B., and E.J. Crossman. 1973. Freshwater Fishes of Canada. Fisheries Research Board of Canada, Ottawa, ON, Canada. 966 pp. Secor, D.H., J.M. Dean, and E.H. Laban. 1992. Otolith removal and preparation for microstructural examination. Special Publication of the Canadian Journal of Fisheries and Aquatic Sciences 117:19–57. Sly, P.G., and D.O. Evans. 1996. Suitability of habitat of Lake Trout spawning. Journal of Aquatic Ecosystem Health. 5:153–175. US Environmental Protection Agency (USEPA). 2016. Cross-state air pollution rule and acid rain program: 2016 program progress. Available online at https://www3.epa.gov/ airmarkets/progress/reports/index.html. Accessed 15 February 2018. Wetzel, R.G. 1975. Limnology. W.B. Saunders Company, Philadelphia, PA. 743 pp.