Street, Gainesville, Florida, 32653, USA b U.S. Geological Survey, Southeast Ecological Science Center, 7920 North West 71st Street,

This article was downloaded by: [University of Florida] On: 02 February 2013, At: 10:07 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Transactions of the American Fisheries Society Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/utaf20 Evaluating the Potential for Stock Size to Limit Recruitment in Largemouth Bass Micheal S. Allen a, Mark W. Rogers a, Matthew J. Catalano a, Daniel G. Gwinn a & Stephen J. Walsh b a School of Forest Resources and Conservation, University of Florida, 7922 North West 71st Street, Gainesville, Florida, 32653, USA b U.S. Geological Survey, Southeast Ecological Science Center, 7920 North West 71st Street, Gainesville, Florida, 32653, USA Version of record first published: 19 Aug 2011. To cite this article: Micheal S. Allen, Mark W. Rogers, Matthew J. Catalano, Daniel G. Gwinn & Stephen J. Walsh (2011): Evaluating the Potential for Stock Size to Limit Recruitment in Largemouth Bass, Transactions of the American Fisheries Society, 140:4, 1093-1100 To link to this article: http://dx.doi.org/10.1080/00028487.2011.599259 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

Transactions of the American Fisheries Society 140:1093 1100, 2011 C American Fisheries Society 2011 ISSN: 0002-8487 print / 1548-8659 online DOI: 10.1080/00028487.2011.599259 ARTICLE Evaluating the Potential for Stock Size to Limit Recruitment in Largemouth Bass Micheal S. Allen,* Mark W. Rogers, Matthew J. Catalano, and Daniel G. Gwinn School of Forest Resources and Conservation, University of Florida, 7922 North West 71st Street, Gainesville, Florida 32653, USA Stephen J. Walsh U.S. Geological Survey, Southeast Ecological Science Center, 7920 North West 71st Street, Gainesville, Florida 32653, USA Abstract Compensatory changes in juvenile survival allow fish stocks to maintain relatively constant recruitment across a wide range of stock sizes (and levels of fishing), but few studies have experimentally explored recruitment compensation in fish populations. We evaluated the potential for recruitment compensation in largemouth bass Micropterus salmoides by stocking six 0.4-ha hatchery ponds with adult densities ranging from 6 to 40 fish over 2 years. Ponds were drained in October each year, and the age-0 fish densities were used as a measure of recruitment. We found no relationship between stock abundance and recruitment; ponds with low adult densities produced nearly as many recruits as the higher-density ponds in some cases. Both prey abundance and the growth of age-0 largemouth bass declined with age-0 fish density. Recruit abundance was highly variable both within and among the adult density groups, and thus we were unable to identify a clear stock recruit relationship for largemouth bass. Our results indicate that reducing the number of effective spawners via angling practices would not reduce recruitment over a relatively large range in stock size. Estimating the strength of compensatory density dependence is a fundamental problem in natural resource management. The degree to which populations compensate for human-induced changes in survival, growth, and reproduction has implications for resource management strategies such as harvest policies and habitat alterations. Compensation in fish populations is thought to occur mainly through changes in survival during larval and juvenile life phases. Across many species and life history types, per capita recruitment rates increase as population size decreases (Cushing 1975; Myers et al. 1999; Rose et al. 2001), resulting in stable average recruitment levels across a wide range of adult abundances (i.e., compensation; Walters and Martell 2004). Measuring compensation in juvenile fish survival is difficult in field studies because (1) long time series of stock and recruit abundance are required, (2) measures of stock and recruitment include a high degree of uncertainty, and (3) direct estimates from experimental density manipulations are rare (Walters and Martell 2004). Most marine fish stock assessments incorporate compensation with stock recruit relationships (e.g., Ricker or Beverton Holt models). Parameters of these models can be estimated by fitting empirical models to time series data of adult abundance and recruitment, which are typically estimated from age-structured stock assessment models. DeGisi (1994) experimentally manipulated populations of brook trout Salvelinus fontinalis in seven Sierra Nevada mountain lakes in California, and Myers (2002) concluded from those data that per capita recruitment increased 19-fold at low stock densities relative to the unfished density. Such experimental manipulations are logistically infeasible in most field settings; thus, experimental measures have seldom been obtained. *Corresponding author: msal@ufl.edu Received August 4, 2010; accepted February 15, 2011 1093

1094 ALLEN ET AL. Measures of recruitment compensation for freshwater fish species are rare because of the lack of long-term data on stock and recruit abundance. Long-term stock and recruit data are largely limited to the Great Lakes, experimental research stations, or at locations where monitoring has been required for resource allocation purposes (e.g., treaty agreements). Hansen et al. (1998) estimated Ricker stock recruitment curve parameters for a population of walleye Sander vitreus. Myers et al. (1999) obtained field estimates of recruitment compensation for a few freshwater and anadromous species, but their review primarily identified stock recruit parameters for marine fish species. Largemouth bass Micropterus salmoides support important freshwater fisheries, but few previous studies have identified a stock recruitment relationship that could be used to infer compensation in recruitment. Jackson and Noble (2000) found that a Ricker stock recruit curve explained about 20% of the variation in age-0 largemouth bass catch rates at Jordan Lake, North Carolina. Reynolds and Babb (1978) detected a Ricker-type stock recruit curve across 37 Missouri ponds, peak age-0 fish densities (800/0.405 ha) occurring at about 10 adult largemouth bass/0.405 ha. Bennett et al. (1969) found that the number of largemouth bass fry produced was not an effective predictor of year-class strength at Ridge Lake, Illinois, suggesting compensatory juvenile survival. Kramer and Smith (1962) noted that largemouth bass year-class strength was set before fry dispersal at two Minnesota lakes, which could indicate weak densitydependent mortality due to protection of fry by adults. However, variation in juvenile largemouth bass survival rates during the first year of life is common (Miranda and Hubbard 1994; Olson 1996; Ludsin and DeVries 1997; Slaughter et al. 2008), which suggests the potential for strong compensatory changes in survival in some instances. Because largemouth bass and other centrarchids are nest brooders, researchers and anglers have expressed concern that catch-and-release fishing during spawning can lower recruitment. Removing adults from spawning beds can reduce individual nest success via nest predators (Kieffer et al. 1995; Philipp et al. 1997; Ridgway and Shuter 1997; Suski et al. 2003), but no studies have shown whether this could reduce recruitment and ultimately influence adult fish abundance. The degree of compensatory change in juvenile survival rates will determine the population-level implications of harvest and reduced nest success via catch-and-release fishing. Gwinn and Allen (2010) simulated effects of reduced nest success on largemouth bass recruitment, but they assumed a level of recruitment compensation based on a literature review of short-lived predators (Myers et al. 1999). Thus, there is a need to understand the degree to which changes in early life survival of largemouth bass can compensate for reduced reproductive output, which would allow for an informed assessment of how angling practices (e.g., harvest, release mortality, tournaments, and nest fishing), stocking rates, and habitat alterations will influence largemouth bass recruitment and abundance. Our objective was to evaluate the potential for recruitment compensation for largemouth bass. We used a pond experiment to address this objective, and we explored the mechanisms by which recruitment compensation could occur by assessing prey abundance for age-0 fish and density-dependent growth. METHODS We manipulated the reproductive output of largemouth bass by varying the number of adults stocked into 0.405-ha hatchery ponds and evaluated recruitment to the fall. We stocked six experimental ponds located at a U.S. Geological Survey facility in Gainesville, Florida, with brood largemouth bass in early January 2007 and 2008. All ponds were drained prior to experiment initiation, between years 1 and 2, and at the end of year 2. Reproductive output was manipulated by varying the number of adult largemouth bass across ponds and by standardizing all fish to between 350- and 450-mm total length (TL). The number of adults stocked in each pond ranged from 6 to 40 each year, which resulted in a range of total adult largemouth bass biomass that was representative of natural Florida populations in 60 lakes sampled by Hoyer and Canfield (1996). We stocked adult largemouth bass such that two ponds received six, one pond received 20, two ponds received 30, and one pond received 40 in each year. Two ponds each year received six adult largemouth bass so that the experiment would have replicate levels of the low adult abundance treatment. The 6- and 40-fish ponds represented extreme low and high values from Hoyer and Canfield (1996), whereas the 20- and 30-fish ponds represented the approximate average conditions across Florida lakes. The adult stocking densities were randomly assigned to ponds each year. We attempted to stock adult largemouth bass at a 1:1 sex ratio in each pond. Adult gender was estimated by probing the urogenital opening with a 1.0-mm diameter plastic tube (Benz and Jacobs 1986), and we evaluated our efficacy to identify gender by sacrificing a random sample of 23 adult fish, which were evaluated by two independent people to verify fish gender. Ponds were stocked with broodfish in early January and drained in October to assess age-0 fish abundance. Abundance and size structure of age-0 largemouth bass in fall is generally indicative of age-1 recruit abundance in Florida (Rogers and Allen 2009); thus, draining the ponds in October served as our index of recruit abundance. Ponds were also stocked with prey and age-1 largemouth bass to serve as predators. We stocked a total of 24 33 kg/ha of bluegill Lepomis macrochirus and redear sunfish L. microlophus in each pond. The Lepomis spp. stocked ranged from 4- to 25-cm TL in all ponds in order to serve as both prey for the adult largemouth bass and to provide broodfish to spawn and provide prey for age-0 largemouth bass. Golden shiner Notemigonus crysoleucas were also stocked as forage in all ponds at rates of 2 4 kg/ha. The size distributions and total biomass of prey stocked was similar for all ponds. Age-1 largemouth bass ranging from 80- to 200-mm TL were stocked at densities of

STOCK SIZE AND RECRUITMENT IN LARGEMOUTH BASS 1095 80 per pond to serve as predators on the age-0 largemouth bass. The age-1 predator stocking densities were determined from historical data from Florida lakes (Hoyer and Canfield 1996) such that each pond would have approximately average abundance of age-1 largemouth bass predators. Ponds were aerated continuously through the summer months to prevent fish kills. To quantify reproductive output, we conducted snorkel surveys to measure the number of nests that produced eggs and fry within each pond. Ponds were snorkeled twice weekly from February to May each year, during the time when nests were present. Nests were marked with fluorescent tape to prevent recounts, and nests were considered successful if they were occupied by a guarding male and had swim-up fry (Philipp et al. 1997; Suski et al. 2003). Age-0 largemouth bass, predator, and prey fish densities in October were obtained by draining the ponds and a sampling design. Owing to the relatively large size of the ponds, obtaining an accurate count of the fish was difficult because of fish being trapped in bottom sediments in proximity of the catch basin. We conducted quadrat sampling in the sediment of the lower one-third of each pond bottom to estimate the number of age-0 fish that were not collected in the catch basin. Total density of age-0 fish, predators (i.e., non age-0 largemouth bass), and prey fish were each obtained by summing the number recovered in the catch basin and the quadrat-estimated number of fish that were trapped in the sediment after draining each pond. We evaluated the evidence for recruitment compensation by exploring hypotheses about the effects of stock size on recruit abundance. The hypotheses we considered were (1) a proportional relationship between stock size and recruit abundance (i.e., a zero intercept linear regression, R = bs), (2) a Beverton Holt asymptotic relationship (R = as/[1 + bs]), and (3) a Ricker dome-shaped relationship (R = ase bs ). Values of R represent recruits, and S is the stock size (number of adults). The proportional relationship infers no recruitment compensation, whereas the Beverton Holt model has increasing recruits per spawner as spawner abundance declines. The Ricker model allows compensation at low stock sizes and overcompensation (i.e., lower absolute recruitment) at high stock abundances, as is typically associated with cannibalism (Ricker 1975). We fitted each model using lognormal distributions and maximum likelihood estimation. Errors in stock recruitment relationships are typically assumed to follow the lognormal distribution because recruitment is the product of survival rates through several early life stages. We tested the evidence for each model using Akaike information criterion corrected for small sample size (AIC c ; Anderson 2008). We considered AIC c values exceeding 8 as indication that a model had substantially less data support than the most credible model (the model with the lowest AIC c value). We evaluated evidence for prey limitation and densitydependent growth for age-0 largemouth bass. We used leastsquares nonlinear regression to assess whether biomass of bluegill vulnerable to predation by age-0 largemouth bass declined with age-0 fish density. We considered bluegill vulnerable to age-0 largemouth bass if they were less than one-third of age- 0 largemouth bass mean total length in each pond (Lawrence 1958; Shelton et al. 1979; Garvey and Stein 1998). Nonlinear regression was also used to evaluate whether age-0 largemouth bass total length (mm) varied with age-0 fish density. We evaluated habitat and predation risk factors that could have confounded the relationship between stock and recruits across ponds. All ponds were treated with fluridone to control growth of hydrilla Hydrilla verticillata, but the abundance of hydrilla still varied among ponds. We measured the percent of pond volume inhabited by hydrilla (PVI) for each pond with a Lowrance LCX-26c HD sonar and Global Positioning System. At least 50 random samples from all points on each pond were taken and measured for pond depth and plant height to obtain a percent of pond volume inhabited by aquatic plants (PVI; Florida Lakewatch 2007). Aquatic plants provide refuge from predation (Savino and Stein 1982), and juvenile survival of centrarchids is often influenced by aquatic plant coverage in lakes and reservoirs (Crowder and Cooper 1982; Bettoli et al. 1993; Hoyer and Canfield 1996; Miranda and Pugh 1997). Thus, variation in hydrilla abundance across ponds could influence our results by mitigating predation risk. We evaluated whether aquatic plant PVI was related to age-0 largemouth bass density (i.e., recruitment) across ponds using correlation analysis. We assessed whether the number of adults (stock size) was related to aquatic plant PVI because a relationship between stock abundance and plant abundance could mask a stock recruit relationship by altering juvenile survival through factors other than stock size (e.g., predation risk). We further assessed whether the density of non age-0 largemouth bass predators present upon draining the ponds was related to hydrilla PVI, which also indicated whether predation risk varied with aquatic plant PVI. RESULTS Our procedure for determining adult fish gender was effective. Gender assignment was correct for 91% of the 23 sacrificed fish, as verified by both independent examiners, indicating that we were successful in establishing an approximate 1:1 sex ratio of age-1 largemouth bass stocked into each pond. This removed the possible confounding effect of variable sex ratio on reproductive output among stock density treatments. We found nesting largemouth bass from February to early May in both years, and we found no evidence that the timing of spawning varied with adult abundance. The two 30-fish ponds in 2008 had poor visibility due to turbidity, which precluded estimating the total number of successful nests in those ponds. The number of successful nests was positively related to the number of adults for the remaining ponds (P < 0.01). Fish re-nested in some cases because a six-fish pond produced six nests in one pond (Figure 1). In order to use all replicates, adult

1096 ALLEN ET AL. FIGURE 1. Number of successful largemouth bass spawning nests as a function of the number of adults stocked for the 10 sample ponds for which the number of nests was estimable. Two of the ponds with six adults produced two nests (N = 4 total). density was used as the measure of reproductive output in the subsequent analyses. Adult density was not a strong predictor of recruitment. The number of age-0 largemouth bass produced across ponds ranged from 98 to nearly 1,150 fish/0.405 ha in October of both years combined (Figure 2). The highest age-0 (recruit) density occurred in the 40 adult fish pond in 2008, and the second highest (900 per 0.405 ha) occurred in a six-adult fish pond in 2009. Age-0 density was highly variable both across and within the adult density groups. Fish ponds stocked with six adults produced a range of 100 900 age-0 fish. Similarly, the 30-adult ponds showed large variation in recruitment (ranging from 100 to 700 age-0 fish; Figure 2). Our analysis did not support a single stock recruitment model that best fit the data owing to the high variability in recruitment within and among adult density values. The Beverton Holt curve had the lowest AIC c value, but the support for this value was not substantially stronger than the proportional ( AIC c = 1.9) and Ricker ( AIC c = 0.87) curves. The similarity of support among these models resulted because of high variability among the ponds and no apparent impact of stock size on recruitment (Figure 2), and the amount of variation in recruitment explained by stock size was less than 10% for all models. Overall, the experiment showed potential for recruitment compensation because we found that ponds with six adults could produce similar recruitment as a 40-adult pond in some cases, suggesting cases of higher recruits per spawner at low spawner abundance. Average recruitment per adult in the six-fish ponds was nearly three times higher (75 recruits/adult) than average recruitment per adult in the 40-fish ponds (24 recruits/adult), which suggests some density dependence in juvenile survival. Nevertheless, we were unable to identify a single stock recruit curve that best fit the data, supporting the hypothesis that recruitment was not dependent on stock abundance for the range of stock sizes we evaluated. We found evidence of relative prey limitations with increasing age-0 largemouth bass density and density-dependent growth. Biomass of bluegill that were of vulnerable size to age-0 largemouth bass declined with age-0 fish density across ponds (P < 0.001; Figure 3). Length frequencies of age-0 largemouth bass were unimodal, making mean total length a suitable measure of fish growth. The nonlinear regression showed a significant decline in mean total length with age-0 largemouth bass density (P < 0.01; Figure 3). Mean length of age-0 fish ranged from 6 to 18 cm (Figure 3), with the highest value representing a six-adult pond that produced 100 age-0 fish in 2009. The lowest mean length (5.9 cm) occurred for a 30-adult pond in 2008 that produced 505 age-0 fish. Thus, we found evidence for top-down effects of age-0 largemouth bass on bluegill prey biomass and evidence for density-dependent growth of age-0 fish. Aquatic plant abundance across ponds did not vary in a systematic way that would be expected to confound a stock recruit relationship. Hydrilla PVI ranged from 7% to 90% across ponds but was not related to the number of adults stocked or age-0 largemouth bass density (Figure 4). We found that non-age- 0 largemouth bass predator density was positively related to hydrilla PVI (Figure 4). However, this would likely stabilize predation risk across ponds, which would reduce variability in the data. Thus, aquatic plant abundance varied across ponds but did not vary with stock abundance or predator density in a manner that would be expected to mask a stock recruit relationship. FIGURE 2. Age-0 largemouth bass density (fish/0.405 ha) versus the number of adults for the 12 sample ponds. Predicted values for the proportional, Beverton Holt, and Ricker stock recruit models are shown. DISCUSSION Fisheries evaluations have found that high variability in stock recruit relationships is universal (Ricker 1975; Walters

STOCK SIZE AND RECRUITMENT IN LARGEMOUTH BASS 1097 FIGURE 3. Vulnerable prey (bluegill) biomass (kg/0.405 ha; top panel) and age-0 largemouth bass mean total length (mm; bottom panel) as functions of age-0 largemouth bass density (fish/0.405 ha). and Martell 2004), and the results of our pond study also showed high variability in recruit abundance across a wide range of stock sizes. We were unable to demonstrate compelling support for a proportional stock recruit relationship versus either of the two forms of density-dependent stock recruit curves. Thus, the data suggested that recruitment was not predictable from adult density. Weak associations between stock size and recruitment have caused researchers to argue that recruitment is determined by environmental factors rather than stock abundance (summarized by Van den Avyle and Hayward 1999). Obviously, recruitment is influenced by stock size at very low stock levels, and it is possible that our low and high fish treatments were not extreme enough to elucidate the shape of the stock recruit curve. Reynolds and Babb (1978) found that peak average largemouth bass recruitment occurred at 10 adults/0.405 ha in Missouri ponds, whereas our low adult treatments had six adults/0.405 ha. We did not see a decline in recruitment at higher stock densities as shown by Reynolds and Babb (1978). The range in adult abundance in our ponds represented extreme values across Florida lakes (Hoyer and Canfield 1996); thus, our values should apply to the expected ranges for natural largemouth bass populations. FIGURE 4. Number of adults (top panel), age-0 largemouth bass density (fish/0.405 ha; middle panel), and predator density (predators/0.405 ha; bottom panel) versus the percent of pond volume occupied by aquatic plants (PVI). Correlation coefficients and P-values are shown for each relationship. Our experiment also suggested that high variability in recruits for each level of stock size is not simply owing to sampling variability and biases in observing stock and recruits from wild populations. Observation error associated with sampling stock and recruits adds considerable uncertainty to these relationships (Rose et al. 2001), but in our study the ponds were stocked with known numbers of adults and recruits were estimated by draining the ponds, thus minimizing observation error.

1098 ALLEN ET AL. Time series autocorrelation also biases stock recruit estimates because adult abundances are dependent on past recruitment (Walters and Martell 2004), but we negated this bias because the stock recruit observations were independent across ponds. Despite eliminating these problems common to empirical studies, our data showed high variability in recruits across the range of stock sizes. This infers that stock recruit relationships may be weak relative to other mechanisms driving recruitment. Because of high variability in the recruitment process, measuring stock recruit relationships will be even more difficult in wild stocks, and more manipulative experiments should be conducted for investigating density-dependent compensation in fish recruitment. A few field investigations have shown potential for recruitment compensation in black bass recruitment. Reynolds and Babb (1978) found a dome-shaped stock recruit curve for largemouth bass in Missouri ponds. Weidel et al. (2007) conducted a whole-lake removal of nonnative smallmouth bass M. dolomieu at Little Moose Lake, New York. They estimated about a 90% reduction in abundance of adult fish, yet both recruitment and total smallmouth bass abundance increased after harvest was initiated (Weidel et al. 2007; Zipkin et al. 2008). Zipkin et al. (2008) built a simulation model using the same data from Little Moose Lake and showed that overcompensation (i.e., Ricker stock recruit curve) was credible for that population. Our study showed similar average recruitment for low versus high stock sizes of largemouth bass, and thus we did not find evidence that recruitment increased as stock density declined. Prior to harvest, the Little Moose Lake smallmouth bass population was a very-high-density population with fish exhibiting slow growth (Weidel et al. 2007). It is possible that our high adult density treatments were not high enough to elicit an overcompensatory response, and future evaluations should explore if this occurs for largemouth bass populations. Differences in age-0 fish growth rates could have influenced predation mortality among ponds. Age-0 fish growth rates were inversely related to density, indicating potential for relative resource limitation at high age-0 fish densities. Juvenile fish survival rates are often positively related to fish growth and size (Houde 1997), and thus smaller age-0 largemouth bass would be expected to have higher mortality rates than larger fish. Wicker and Johnson (1987) found that age-0 largemouth bass in Florida had high mortality when prey resources were lowest in early summer. We found that prey abundance was negatively related to age-0 largemouth bass density and that growth was density dependent. Slaughter et al. (2008) found that growth and survival of age-0 largemouth bass were positively related in some cases and not others in a pond experiment. However, Jackson and Noble (2000) found no evidence for densitydependent growth of age-0 largemouth bass through time in a large reservoir. Recruitment was not related to stock abundance in this study, but we did find density-dependent growth of age-0 fish which could have influenced survival rates across ponds. Density-dependent spawning of adult fish is another potential mechanism for recruitment compensation. Ridgway et al. (2002) and Dunlop et al. (2007) showed that the proportion of male smallmouth bass that build nests declines with male abundance. Skip spawning by females is reported for many fish species, and the occurrence of skip spawning can be dependent on the amount of available food resources (Rideout et al. 2005). Thus, the proportion of adults that spawn could be influenced by adult density, which would cause the number of nests to decline with stock abundance. Bennett et al. (1969) noted that the number of adult largemouth bass had either no effect or a negative impact on the number of fry produced. Our four ponds with six adults had three to six successful nests, indicating that some males renested through the spawning season. Conversely, the 30 and 40 fish ponds had only about half as many nests as adults stocked (Figure 1). The number of successful nests was positively related to the number of adult stocked in this study, suggesting that adult density was an effective measure of overall reproductive output. However, more work is needed to determine whether density-dependent nesting activity of adult fish is a mechanism for recruitment compensation in black bass populations. Our study attempted to isolate the effect of stock size on recruitment, but like many pond studies, other factors varied across ponds that could have influenced our results. Variation in aquatic plant PVI among ponds may have influenced predation risk for age-0 fish. Our relatively low sample size (N = 12 ponds) precluded estimation of interaction effects between aquatic plant PVI and stock size. However, aquatic plant PVI did not vary in a systematic manner that would be expected to directly confound the effect of stock size. Owing to turbidity in two ponds during 2008, we were unable to use the number of successful nests or total egg production as a measure of reproductive output and instead used the number of adults stocked. This could have contributed to the variation in responses across ponds, particularly if the average number of eggs produced per nest varied across adult treatments. The number of eggs in largemouth bass nests is positively related to fish size (Philipp et al. 1997), and we attempted to control for this by stocking a narrow and similar size range of adults in all ponds. However, measures of total egg production rather than stock size could potentially reduce the variation in responses in future studies. We did not identify a specific form of a stock recruit relationship for largemouth bass, but our study has implications regarding the importance of angling on recruitment. The results indicated that largemouth bass recruitment is not directly dependent on spawning stock density across a wide range of densities. These results infer that reduced nest success via fishing activities (e.g., Philipp et al. 1997) would not be expected to reduce overall recruitment in many instances. Impacts could occur under levels of extreme nest reductions owing to fishing, and the vulnerability of largemouth bass populations to these effects could vary with latitude (Gwinn and Allen 2010). However, our experiment varied adult abundance over a wide range (6 to 40 adults), and we saw no change in average recruitment levels.

STOCK SIZE AND RECRUITMENT IN LARGEMOUTH BASS 1099 More studies are needed to evaluate how recruitment is influenced by reproductive output, but our results showed the loss of nests would not directly reduce largemouth bass recruitment. ACKNOWLEDGMENTS We thank K. Rice, S. Ruessler, and the U.S. Geological Survey Southeast Ecological Science Center for use of hatchery ponds and substantial cooperation and support throughout the project. B. Baker and B. Matthias helped with data processing. Advice on application rates of fluridone was provided by M. Netherland. Conversations with D. Philipp, W. Porak, C. Suski, and C. Walters helped us when conceptualizing this problem. Reference to trade names does not imply endorsement by the U.S. Government. REFERENCES Anderson, D. R. 2008. Model-based inference in the life sciences: a primer on evidence. Springer-Verlag, New York. Bennett, G. W., H. W. Adkins, and W. F. Childers. 1969. 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