BFS Technical Report #28. Limnological and fishery survey of a privately owned fishing preserve

Transcription

1 Editor s Note: Specific information related to the location of this site has been redacted for landowner s privacy. BFS Technical Report #28 Limnological and fishery survey of a privately owned fishing preserve PREPARED BY M. Albright, H. Waterfield SUNY College at Oneonta Biological Field Station and M. Cornwell, K. Coakley, J. Lydon SUNY Cobleskill Department of Fisheries and Wildlife

2 INTRODUCTION Twelve Mile Pond ( o N, o W), is located in Pike County, Pennsylvania at 1181feet (360m) in elevation. At approximately 190 acres (77 hectares), it is a natural lake of glacial origin comprised of two basins divided by what is likely a submerged esker (Trembley 1953). The basins are approximately circular; maximum depths encountered in the eastern and western basins were 31 feet (9.5 m) and 35 feet (10.7 m), respectively. The bar dividing the basins drops from about 3 feet (1 m) near the north shore to about 10 feet (3 m) at the south shore. Though not measured, the lake s watershed is small relative to the size of the waterbody. A few wetland seeps are present along its perimeter, though there are no channelized incoming flows. The discharge at the outlet implies that ground water inflow is substantial. This study serves to provide current information on the lake s ecology (focusing on its fishery) and its physical and chemical limnological characteristics. Information collected here is compared to the findings of a 1953 study by F.J. Trembley to provide insight into changes in character over the past 57 years. Management recommendations for the lake, primarily related to fisheries management, are provided. Trembley (1953) reported that he found the fishery comprised 11 species of mostly cool/warm water fishes including: (1) largemouth bass (Micropterus salmoides), (2) smallmouth bass (Micropterus dolomieu), (3) pumpkinseed (Lepomis gibbosus), (4) bluegill (Lepomis macrochirus), (5) redbreast sunfish (Lepomis auritis) (6) yellow perch (Perca flavescens), (7) golden shiner (Notemigonus chrysoleucas), (8) chain pickerel (Esox niger), (9) brown bullhead (Ameiurus nebulosus), (10) rock bass (Ambloplites rupestris) and(11) alewife (Alosa pseudoharengus). The lake has been stocked with a mix of brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) most years since the 1950s, though there is no record of angling success for these cold water species. An important component the current survey is to evaluate the lake s ability to sustain these game fish. Though the main interest of the landowner is the fishery, limnological data are critical in understanding the conditions present in the water body and the resulting availability of habitats for fish species that inhabit the lake system. Trout species are intolerant of temperatures exceeding 70 o F (20 o C) and they require sufficient dissolved oxygen for respiration, generally at least 5 mg/l. During the summer months, lakes stratify due to temperature differences from top to bottom. A warm layer occupies the surface of the lake, with a cooler layer in deeper waters. Those deeper waters, being isolated from the atmosphere, are prone to oxygen depletion through processes of decomposition. The extent to which lakes lose oxygen in their deeper water is a function of their depth and production (amount of algae growing). The fish community was surveyed via pelagic (open water) gill netting and electrofishing of littoral areas. Measurements of physical water quality were taken on-site; samples were collected for the determination of total nitrogen, nitrate, phosphorus, calcium, chloride, and chlorophyll a concentrations as well as for characterization of the zooplankton community.

3 LIMNOLOGY METHODS On 12 June 2010, 12 Mile Pond was visited by the authors. Preliminary reconnaissance efforts yielded an understanding of the general bathymetry and depth range throughout the pond, identified the deepest sites in each the east and west basin and included a brief, qualitative survey of rooted plants. At the deepest site in each basin (Figure 1), water samples were collected in profile from the surface to the bottom in three meter intervals. Upon return to the lab, they were analyzed for total phosphorus, total nitrogen and nitrate. Samples from the surface and bottom were also tested for chloride, calcium and alkalinity (a measure of the acid buffering capacity of the water). Table 1 provides analytical methods utilized. A Eureka water quality multiprobe was used to collect ph, dissolved oxygen, temperature and conductivity from the surface to the bottom at one meter intervals. Secchi disk transparency was measured at both profiling sites. Zooplankton were collected using a 63 µm net. They were preserved in ethanol and later were examined under a microscope where they were identified and measured using an ocular micrometer. Samples for chlorophyll a analysis were collected just below the surface; duplicate 100 ml aliquots were filtered on site through Whatman GF-A filters; they were stored on ice and then frozen until further processing. Analysis involved an extraction with buffered acetone and a fluormetric determination. Figure Mile Pond, Pike County, PA. The 2 water quality profiling sites are indicated.

4 Table 1. Laboratory procedures used in analysis of water samples. Parameter Sample Volume Preservation Method Reference Total Phosphorus-P 10 ml H 2 SO 4 to ph<2 Total Nitrogen-N 5 ml H 2 SO 4 to ph<2 Persulfate digestion followed by single reagent ascorbic acid Cadmium reduction method following peroxodisulfate digestion Liao and Marten 2001 Pritzlaff 2003; Ebina et. al 1983 Nitrite+Nitrate-N 10 ml H 2 SO 4 to ph<2 Cadmium reduction Pritzlaff 2003 Ammonia-N 10 ml H 2 SO 4 to ph<2 Phenolate Liao 2001 Calcium 50 ml None EDTA titrimetric EPA 1983 Chloride 100 ml None Mercuric nitrate titration APHA 1989 Alkalinity 100 ml Cool to <4 o C, measure ASAP Titration to ph=4.6 APHA 1989 Chlorophyll a 100 ml Ice sample, filter ASAP, process in reduced light Fluorometric Welshmeyer 1994 LIMNOLOGY RESULTS AND DISCUSSION Physical water quality Temperature and Oxygen Table 2 contains and Figures 2 and 3 illustrate dissolved oxygen and temperature profiles in the east and west basins, respectively. Both temperature and dissolved oxygen profiles were similar between the basins. The lake was thermally stratified in both basins, with thermoclines present from 2 to 4m. Surface waters averaged 20.8 and 21.2 o C in the east and west basin, with averages of 11.7 and 11.3 o C below 4m depth. Dissolved oxygen concentrations were nearly saturated in the upper layers, but declined below the thermocline, approaching zero near the bottom. Because the deeper, cooler water is isolated from the atmosphere, oxygen levels there will continue to decline until the lake mixes. Mixing occurs when the temperature of the water is nearly the same from top to bottom, allowing the water to mix (and re-oxygenate) with modest wind-driven currents. During Trembley s work on 30 July (1953), the lake was unstratified, being about 24 o C (76 o F) from top to bottom, indicating that the lake was experiencing overturn.

5 It would be interesting to know if that year was typical; it is the author s opinion that given the strength of stratification in mid-june 2010, turnover would not likely occur until much later than 30 July. Between the time of oxygen-loss in the deep water until fall turnover, that layer is not available to fish. In fact, cold water fish such as trout require at least 5 mg/l dissolved oxygen. Figure 2. Dissolved oxygen (mg/l) and temperature ( o C), measured in profile on 12 June 2010, in the east basin of 12 Mile Pond, PA. Figure 3. Dissolved oxygen (mg/l) and temperature ( o C), measured in profile on 12 June 2010, in the west basin of 12 Mile Pond, PA.

6 Table 2. Physical and chemical water quality data collected 12 June 2010 in the east and west basins of Twelve Mile Pond, PA. East Basin Depth Dissolved Oxygen ph Conductivity Nitrate + Nitrite Total Nitrogen Total Phosphorus Calcium Alkalinity Chlorides Temperature meters C F mg/l ms/cm mg/l mg/l µg/l mg/l mg CaCO 3 mg/l 0m m m m bd m m m bd m m m bd Chlorophyll a (µg/l) 8.4 Secchi Disk Transparency 2.2 meters West Basin Depth Dissolved Oxygen ph Conductivity Nitrate + Nitrite Total Nitrogen Total Phosphorus Calcium Alkalinity Chlorides Temperature meters C F mg/l ms/cm mg/l mg/l µg/l mg/l mg CaCO 3 mg/l 0m bd m m m bd m m m bd m m m bd Chlorophyll a (µg/l) 5.6 Secchi Disk Transparency 2.4 meters

7 ph ph profiles for both basins are shown in Figure 4 and Table 2. The wide fluctuations (of almost 2 units in the east basin) imply the lake is poorly buffered against changing acidity levels (see ions below). During periods of thermal stratification, ph is lower (that is, the water is more acidic) in the deeper waters. The same process that uses up oxygen there (decomposition of organic material) is generating carbon dioxide which, in water, forms carbonic acid. This is yet another stress for organisms which might otherwise occupy these deeper waters. Optimal ph for most aquatic organisms is 6.5 to ph Depth (m) East Basin ph West Basin ph Figure 4. ph, measured in profile on 12 Jun 2010, in east and west basins of 12 Mile Pond, PA. Chemical water quality Nutrients Nitrogen and phosphorus are key nutrients in determining the productivity of aquatic systems (i.e., the extent of algal growth). Profiles of total nitrogen and total phosphorus are given in Figures 5 and 6 and Table 2. Nitrate (the form of nitrogen that is directly available for algal growth) concentrations in the lake were below detection with the exception of the east basin surface sample, which had a very low concentration. The low nitrate concentrations, combined with the fact that total nitrogen was present at mg/l, indicates that most nitrogen is organically bound, suggesting that algal growth and productivity is limited by the availability of nitrate-n in the water column. Phosphorus concentrations were detectable, but low, as would be expected in such a protected and pristine watershed, such as we find at Hunter s Range. The increased phosphorus concentration near the bottom, particularly in the west basin, illustrates internal phosphorus loading, which is the release of phosphorus from bottom sediments which occurs in the absence of oxygen.

8 0 Total Nitrogen Profiles Total Nitrogen (mg/l) Depth (m) East Basin TN West Basin TN Figure 5. Profiles of total nitrogen on 12 June 2010, in the east and west basins of 12 Mile Pond, PA. 0 Total Phosphorus Profiles Total Phosphorus (ug/l) Depth (m) East Basin TP West Basin TP Figure 6. Profiles of total phosphorus on 12 June 2010, in the east and west basins of 12 Mile Pond, PA.

9 Ions: Conductivity, Alkalinity, Calcium, and Chloride The water of 12 Mile Pond is very soft. Conductivity (an indirect measure of dissolved ions in the water) was very low, between 0.02 and 0.03 ms/cm (Table 2). Incidentally, this low conductivity was the reason that the electrofishing efforts were not wholly effective. The water did not conduct the electrical current well. Productive fisheries tend to have conductivity values between 0.1 and 0.3 ms/cm. Alkalinity is a measure of how well water is buffered against changes in ph; it is generally linked to calcium (as calcium carbonate most often provides this buffer). Alkalinty was expectedly low, ranging from 3.0 to 4.0 mg/l (as calcium carbonate) (Table 2). The range of these measures, as well as those of ph, fall below the ideal range for gamefish, though barely so. It should be noted that the lake is prone to acidification should it experience acid deposition. Calcium ranged from just 3.2 to 4.0 mg/l from top to bottom in both basins (Table 2). Its concentration is dependent upon local geology which, in eastern Pennsylvania, contains little calcium. Different organisms have greatly varying calcium requirements. Calcium, alkalinity, and conductivity are often closely interrelated. Chloride concentrations were also low, ranging from 1.0 to 1.5 mg/l throughout both basins (Table 2). These low values are natural and reflect the lack of human influence on the lake. Comon sources of human-derived chloride include de-icing salts and wastewater effluent. Chlorophyll a and Secchi Transparency Chlorophyll a is a photosynthetic pigment found in all algae, and its concentration indicates the algal density in the water. Secchi transparency is the depth to which a 20 cm black and white disk is visible. Chlorophyll a concentration in the near-surface waters of the east basin was 8.42 µg/l. Secchi transparency was 2.2 meters. In the west basin, chlorophyll a was 5.63 µg/l and Secchi transparency was 2.4 meters. These measures seem appropriate for a waterbody such as Twelve Mile Pond. In 1953, Trembley recorded the transparency as 12 to 14 feet (about 3.5 m). Given that transparency exhibits great week-to-week variability, it has not changed meaningfully in Twelve Mile Pond. Zooplankton community Zooplankton are open-water animals which graze upon algae and which, in turn, are eaten by foraging fish (including the young of gamefish species). There was a lack of largerbodied zooplankton collected at 12 Mile Pond. This community was dominated by rotifers, which provide forage to only the smallest of fish. Cladocerans and copepods (together, large, crustacean zooplankton) comprised only 17% of the community, and most of those were nauplii (larval copepods). This is presented graphically in Figure 7 and is more fully provided in Table 3. We suspect that the high abundance of juvenile panfish is over-exploiting zooplankton as a food source.

10 Cladocera 1% Copepoda 16% Rotifera 83% Mean size: Cladacera= 0.50 mm Copepoda= 0.30 mm Rotifera= 0.21 mm Figure 7. Graphical summary of the zooplankton community and mean size by taxa collected from 12 Mile Pond, 12 June Table 3. Summary of the zooplankton community and mean size by taxa collected from 12 Mile Pond, 12 June Taxa % Mean length (mm) Cladocera Macrothricidae Copepoda Cyclopoid nauplii Rotifera Asplanchna Kellicotia Keratella Gastropus Plomia Plant community No non-native aquatic plants were noted in 12 Mile Pond, a situation that is quite unique in this day and age. Bladderwort (Utiricularia sp.) was the dominant submerged aquatic macrophyte, and watershield (Brasenia schreberi) was a common floating leaved aquatic plant. Both favor soft, slightly acidic waters. The diversity noted by Trembley (1953) in 1953 was

11 greater, with three species of water lilies, a type of pondweed and the emergent plant pickerel weed (Pontederia cordata) being noted. The differences between the years might be seasonal, as the 1953 survey was conducted about 6 weeks later in the year. Benthic Community Time did not allow for a survey of the benthic (bottom-living animal) community. However, a crayfish which had been collected from a fish s stomach and stored in a freezer was provided for identification, the concern that it was the exotic nuisance rusty crayfish (Orconectes rusticus). It was a member of the genus Orconectes, but unfortunately, due to its life stage, it could not be identified to the specific level. Other members of Orconectes are native to this region. FISHERY SURVEY METHODS Electrofishing is the use of electricity to catch fish. DC electrical current is used to produce a temporary erratic swimming response and anesthetic effect that allows a netter on the front of an electrofishing boat to collect immobilized fish. If done correctly, the effects on the fish are negligible, with all of the fish returned to the water immediately after data collection. The fisheries survey was conducted on the 12 and 13 of June 2010 at night with a Smith- Root boat electrofisher. The survey commenced after dark at 9:00 pm and ended at 2:00 am. The survey was contiguous, and fishing occurred in shallow (<4 ), near shore water in consecutive, connecting electrofishing runs. Seven consecutive survey runs in total were completed around the lake, which are illustrated in Figure 8. Also indicated is the location of the gill net placement (see below). The runs alternated between All Fish (AF) surveys, during which all encountered fish were collected, and Game Fish Only (GFO), during which only game fish species were collected. Electrofishing effort (time in seconds) for each run was automatically recorded by the boat electrofisher. A Lowrance fish finder unit was used to record latitude and longitude coordinates for the start of each electrofishing run. Survey startpoints and effort are recorded in Table 4. A 5000-watt HONDA generator coupled to a Type VI-A variable voltage pulsator provided power for the electrofisher. During the fish collection, DC volts at amps were used. Two netters located on each side of the bow captured fish in the electrical field. Fish were then placed into a 75-gallon live well in the boat and processed at the end of the collection run. After processing all fish were released in good condition. Electrofishing surveys were made when littoral water temperatures were C, as prescribed in the Percid Sampling Manual (Forney et al., 1994), with alternating game fish only (usually min) and all fish (usually min) collections. For the purposes of this survey, perch and crappie were considered gamefish. Collected fish were identified and measured in

12 maximum total length (millimeters) on a measuring board. Results of game fish and non-game fish are expressed in catch/hr on the length frequency histogram for each species (Figures 11-17). These standard survey methods and electrofishing boat design are routinely used by the New York State Department of Environmental Conservation (NYSDEC). A gill net survey was also conducted in addition to the electrofishing. Two types of gill net sets were made. A single 21 meter pelagic (open water) gill net composed of seven panels (5.0, 7.5, 10.0, 12.5, 15.0, 17.5 and 20.0mm bar mesh) was set to fish from the surface and hung down to 6 m deep. It was intended target open water, schooling fish of the epilimnion, such as alewife. The second net was a traditional gill net composed of six (6) twenty-five foot panels of ¾, 1, 1 ¼, 1 ½, 1 ¾, and 2 bar mesh, for 150 of total net fishing from the lake bottom up to 8 off-bottom. This was intended to target deep, cold water oriented fish of the hypolimnion, including trout. Electrofishing data were entered into an EXCEL file. Several metrics were calculated from the data including: (1) Relative abundance: the composition of each species as a percentage of the total community. (2) Catch Per Unit Effort (CPUE): the catch of each species as a function of time, calculated by dividing the number of individuals of each species by the hours fished for that species. This the most widely recognized index of abundance. (3) Length-Frequency Analysis: The number of individuals of each species plotted on a graph clustered by their size. This helps identify year classes and year class failures and allows one to visualize the data and identify trends. (4) Proportional Stock Density: (PSD) is the ratio of quality sized fish to the available stock sized fish. This was calculated for each species. i. PSD= # of quality size / # stock size. (5) Relative Stock Density: (RSD) the ratio of preferred sized fish to stock sized fish i. RSD= # of preferred / # stock size PSD and RSD are numerical descriptors that are often used to understand fish population dynamics. Stock length is defined as the approximate length of maturity of a species (Kohler and Hubert 1999) and is the size fish that an angler is most likely to catch. Stock length fish are the minimum size when a fish enters the fishery. For most prey species, stock length is 5. For largemouth and smallmouth bass, stock length is 8. The actual stock of each species is the number of fish that are at or above the stock length. Quality is the minimum size of fish that most anglers like to catch (Anderson 1978). For prey species, this is typically 8, and for bass it is 12. PSD describes the ratio of these quality sized fish to the stock of that species.

13 Preferred length is approximately 50% of the size of the world record of a particular fish species measured (Gabelhouse 1984). For prey species, this is typically 10, and for bass it is 15. RSD describes the ratio of these preferred sized fish to the stock of that species. Table 4. Study site descriptions of Twelve Mile Pond, Pike County, PA. Site Latitude Longitude Type Seconds Time (Hrs) AF N W AF GFO N W GFO AF N W AF GFO N W GFO GFO N W GFO AF N W AF GFO N W GF AF Effort GFO Effort Total Effort Gill Net N W Gill Net NA NA AF= All Fish Collection GFO= Game Fish Only Collection

14 Figure 8. Aerial image of Twelve Mile Pond, Pike County, PA with electrofishing sites.

15 FISHERY SURVEY RESULTS Table 5 compares the fish species present in Twelve Mile Pond during the 1953 survey (Tembley 1953) and in Alewife was the only species present in 1953 but not It reportedly had been common. Black crappie were collected in the 2010 gill nets. They were not reported in the 1953 survey. Table 5 also provides the size range of fish collected in the 2010 electrofishing survey. Despite repeated plantings of trout, none were collected in either survey. The fish community of Twelve Mile Pond consisted of species representing all suitable niches of a lake environment. Predators, panfish, foragers, planktivores, and scavengers were all present. Figure 9 summarizes the relative abundance of species present. Predatory fish such as largemouth bass (Micropterus salmoides), smallmouth bass (M. dolomieu) and chain pickerel (Esox niger) comprised 18% of the fish population. Panfish, including bluegill (Lepomis macrochirus), pumpkinseed (L. gibbosus), red-breasted sunfish (L. auritus), rock bass (Ambloplites rupestris) and yellow perch (Perca flavescens) together comprised 80.2% of the community. The only scavenger type fish captured were 2 brown bullheads (Ameiurus nebulosus; 0.3%). Golden shiners (Notemigonus crysoleucas), typically a planktivore, though a picker/forager at larger sizes, were collected in low numbers (1.5%). A total of 783 fish were captured. Table 5. Fish population statistics from Twelve Mile Pond, 12 June * No lake chubsuckers were collected, though they were reportedly (unsuccessfully) stocked in the early 1950s Electrofishing Species Trembley Efishing Gill Net Quantity Rel. Abund (%) Size Range (mm) Size Range (in) Alewife X Black Crappie X Bluegill X X Brown Bullhead X X X Chain Pickerel X X Golden Shiner X X X Lake Chubsucker* Largemouth Bass X X Pumpkinseed X X Redbreast Sunfish X X Rockbass X X Smallmouth Bass X X Yellow Perch X X X Total 12 species 11 species

16 Relative Abundance (%) of Fish at 12-Mile Pond 12 June 2010 Yellow Perch, 38.3 Bluegill, 38.9 Smallmouth Bass, 1.4 Rockbass, 0.3 Redbreast Sunfish, 0.5 Pumpkinseed, 2.1 Largemouth Bass, 11.5 Brown Bullhead, 0.3 Chain Pickerel, 5.3 Golden Shiner, 1.5 Figure 9. Relative abundance (%) of fish at Twelve Mile Pond, 12 June Proportional stock density (PSD) is a length-frequency index that breaks the catch of a particular species down into designated sizes. These sizes are the minimum size to be considered to be catchable (stock size), size near the state legal size (quality), and a size that is considered a better catch (preferred). From the length-frequency distribution data (see Figures below), indices of population balance were generated for 6 species of fish, and are presented in Table 6. These indices, proportional stock density (PSD) and relative stock density (RSD), are numerical descriptors that are often used to understand fish population dynamics. Proportional stock density (PSD) is simply the ratio of quality sized fish to the available stock sized fish, while relative stock density (RSD) is the ratio of preferred sized fish to stock sized fish. Stock length is defined as the approximate length of maturity of a species (Kohler and Hubert 1999), quality is the minimum size of fish that most anglers like to catch (Anderson 1978), and preferred length is approximately 50% of the size of the world record of the particular fish species measured (Gabelhouse 1984). In a balanced fishery dominated by largemouth bass, PSD for should be 40-60% (of bass being greater than 12 ), and RSD should be 10-25% (of bass being greater than 15 ). For panfish, PSD should be 20-60% (of fish over 8 ) (Forney 1989). To illustrate an example of one of aforementioned indices, the PSD of yellow perch in Twelve Mile Pond was 24% (see Table 6); meaning 24% of all mature fish are of quality length (> 8 ). The RSD of yellow perch was 16%, thus 16% of the yellow perch population

17 were greater than a preferred catch size to anglers (> 10 ). Both largemouth bass and smallmouth bass had excellent PSD and RSD values, indicating an exceptional fishery for those species. PSD values for chain pickerel and yellow perch were average while their RSD values were poor. No chain pickerel within the preferred size range were captured. Bluegill had a good PSD and poor a RSD, while pumpkinseed s PSD and RSD values were poor. It is recommended by Anderson (1980) that a suitable range of PSD for bluegill and pumpkinseed be However, it should be noted that there were trophy-sized pumpkinseed and bluegill present in the lake. Table 6. Proportional stock density (PSD) and relative stock density (RSD) statistics for Twelve Mile Pond 12 June Bluegill # < Stock size (<5") # Stock Size (5") # Quality Size (8") # Preferred Size (10") PSD RSD (Prey) Pumpkinseed # < Stock size (<5") # Stock Size (5") # Quality Size (8") # Preferred Size (10") PSD RSD (Prey) Redbreast S unfish # < Stock size # Stock Size (5") # Quality Size (8") # Preferred Size (10") PSD RSD (Prey) Sample too small Yellow Perch # < Stock size (<5") # Stock Size (5") # Quality Size (8") # Preferred Size (10") PSD RSD (Prey) Chain Pickerel # < Stock size (<10") # Stock (10") # Quality (15") # Preferred (20") PSD RSD (Predator) Largemouth Bass # < Stock size # Stock (8") # Quality(12") # Preferred(15") PSD RSD (Predator) Smallmouth bass # < Stock size (<8") # Stock (8") # Quality(12") # Preferred (15") PSD RSD (Predator) Prey PSD # < Stock size (<5") # Stock Size (5") # Quality Size (8") # Preferred Size (10") PSD RSD Predator PSD # < Stock size # Stock # Quality # Preferred PSD RSD Another effective use of PSD is to assess the predator to prey balance in a fish population. Figure 10 illustrates a chart with five hypothetical points that can characterize a fishery by its predator to prey PSD ratio. For Twelve Mile Pond, the average PSD value from largemouth bass, smallmouth bass, and chain pickerel was used for the lake s predator PSD (72), while the average PSD from yellow perch, bluegill, and pumpkinseed was used for the lake s prey PSD (29). These values suggest that Twelve Mile Pond has a healthy prey density. However, there are too many large, old predatory individuals. Eventually, the predator/prey density will move towards B or C on the Figure 10 grid, making the fishery comprised of too many large, old individuals or a community of large predators and stunted prey.

18 Figure 10. Tic-tac-toe grid comparing proportional stock densities (PSD) of predators and prey from Twelve Mile Pond (adapted from Kohler and Hubert, 1999). Parallel lines bound the desired PSD ranges. Potential interpretations for the different combinations are A, mutual balance for satisfactory fishing; B, community comprises large, old specimens, indicative of an unfished population; C, stunted prey interfering with predator reproduction, D, overfishing of predators and stunting of prey; and E, high population of small predators excessively cropping young prey. The predator to prey ratio of 12 Mile Pond (72, 29) represented by a plus symbol (+) is in a range described as an under-fished population. Sample sizes of several species of fish were adequately large enough to distinguish age classes from length-frequency histograms (see Figures 11-17). For example, there was an obvious young-of-year, age-1 year class between mm ( ) for largemouth bass. Another obvious year class was in the mm ( ) range and another between mm ( ). Without actual back-calculating data from fish scales, age classes can only be speculated from length-frequency histograms, however the correlation between high frequency of similar length values and year classes is strong. Length-frequency histograms of brown bullhead and rock bass were not provided due to low sample numbers. The 2 brown bullhead captured were 397 and 400 mm (15.8 ) and the 2 rock bass were 205 and 252 mm ( ).

19 Frequency (#) Largemouth Bass Length Frequency 12 June 2010 Boat Electrofishing (56 fish/hr) Figure 11. Length frequency histogram of largemouth bass at Twelve Mile Pond, 12 June Smallmouth Bass Length Frequency 12 June 2010 Boat Electrofishing (5 fish/hr) Length (in) Frequency (#) Length (in) Figure 12. Length frequency histogram of smallmouth bass at Twelve Mile Pond, 12 June 2010.

20 10 Chain Pickerel Length Frequency 12 June 2010 Boat Electrofising (26 fish/hr) Figure 13. Length frequency histograms of chain pickerel in 12 Mile Pond, 12 June Frequency (#) Length (in) Frequency (#) Bluegill Length Frequency 12 June 2010 Boat Electrofishing (359 fish/hr) Length (in) Figure 14. Length frequency histogram of bluegill in Twelve Mile Pond, 12 June 2010.

21 10 Golden Shiner Length Frequency 12 June 2010 Boat Electrofishing (12 fish/hr) Frequency (#) Length (in) Figure 15. Length frequency histogram of golden shiner in Twelve Mile Pond, 12 June Pumpkinseed Length Frequency 12 June 2010 Boat Electrofishing (18.5 fish/hr) Frequency (#) Length (in) Figure 16. Length frequency histogram of pumpkinseed in Twelve Mile Pond, 12 June 2010.

22 120 Yellow Perch Length Frequency 12 June 2010 Boat Electrofishing (186 fish/hr) Frequency (#) Length (in) Figure 17. Length frequency histogram of yellow perch in Twelve Mile Pond, 12 June The two gill nets deployed for an overnight survey yielded low catches. Only 12 individuals were captured from both nets; 1 yellow perch (325 mm; 12.8 ), 5 golden shiners ( mm; ), 2 brown bullhead ( mm; 15.8) and 4 black crappie ( mm; ). Black crappie were not captured during the electrofishing survey, as they inhabit an open water habitat away from the shoreline in Twelve Mile Pond. It should be noted that one of the black crappie individuals was of trophy proportions. There were several very large fish captured at 12 Mile Pond. Some notable catches were a 14 yellow perch, 16 brown bullhead, 10.5 bluegill, a 10 pumpkinseed, 15 black crappie, 19 largemouth bass, and a 16 smallmouth bass (Table 7). Note that in some cases, these (and other) larger fish do not appear in the length frequency graphs (Figures 11-17). This is the case where non-gamefish were collected during Game Fish Only surveys. Their sizes were recorded, but only those fish collected during the appropriate surveys were graphed.

23 Table 7. The largest individual of each fish species captured at Twelve Mile Pond, 12 June Species Metric (mm) English (inches) Yellow Perch Bluegill Pumpkinseed Red-breasted Sunfish Black Crappie Largemouth Bass Smallmouth Bass Chain Pickerel Brown Bullhead Golden Shiner Rock Bass CONCLUSIONS AND MANAGEMENT RECOMMENDATIONS Twelve Mile Pond is a soft water lake that is nearly pristine (minimally impacted by human influence). This softness is a function of the local geology lacking in calcium bearing bedrock. When considering ideal ranges of various parameters for aquatic organisms, most favor conditions involving harder water; that is, waters having higher concentrations of calcium carbonate. This tends to increase a lake s fertility, increases conductivity, and increases alkalinity. Higher alkalinity values lead to higher (and more favorable) ph values, and will help stabilize ph values from undesirable fluctuations. In light of the above, Twelve Mile Pond would likely benefit by the addition of calcium carbonate (or liming the lake). Fish health and production have been realized as the result of such a management strategy. Typical initial application rates are one to two tons of lime per acre of surface area. Given the size of this waterbody, this would be an ambitious endeavor. Another natural, though somewhat undesirable, aspect of the lake involves its tendency to lose oxygen in deeper waters during summer stratification. This is a consequence of the decomposition of organic material, primarily algal cells. The deep strata having less than 5 mg/l is only marginally available habitat for most fish species. As bottom waters loose oxygen, nitrogen compounds are reduced to ammonia, which is highly toxic to all organisms. Various options exist which could incorporate oxygen in deeper waters to address these concerns. Some do so without disrupting the thermal stratification. This might provide suitable habitat for a sustained cold water (trout) fishery.

24 As stated above, Twelve Mile Pond does not contain the appropriate habitat to support a viable trout population given the temperature and oxygen profiles; no trout were collected during electrofishing or gill net surveys, further confirming that previously stocked trout have not survived in any appreciable numbers. It is advised that trout not be stocked toward the goal of establishing or maintaining a trout fishery unless oxygen issues are addressed. Based on relative abundance and community structure, Twelve Mile Pond is a typical centrarchid-dominated fishery. The fish population is dominated by members of the sunfish family (Centrarchidae) such as largemouth bass, smallmouth bass, rock bass, bluegill, pumpkinseed, and redbreast sunfish. Typically, yellow perch and chain pickerel are present with these species, as was the case in Twelve Mile Pond. Although Trembley s previous survey of the lake in 1953 records significantly fewer smallmouth bass with respect to largemouth bass, there is no reason to believe the ratio of these two species has changed drastically, nor that it will. Trembley (1953) was correct in his initial assumption that in lakes with both species of bass, largemouth will outcompete and may even eliminate smallmouth. These two species are able to co-exist in healthy sizes and numbers in Twelve Mile Pond due to the segregated habitats that each of the species prefer. A significant portion of the shoreline is of a steep, rocky nature which smallmouth bass prefer while there was also abundant weedy littoral zone for largemouth bass. Trembley (1953) collected one bluegill in his survey and noted they had been recently introduced. Since then, the bluegill population has become well established, being the most abundant fish in the lake. Several specimens were of a very desirable size for anglers. This expansion in bluegill population growth has put significant pressure on pumpkinseeds and redbreast sunfish, reducing their numbers and increasing the size of individuals. A 10 redbreast sunfish was captured during the survey, which is an unusually large size for this species. In Trembley s previous survey, yellow perch smaller than 11 inches were not captured, and yellow perch as long as 18 inches were. The population of perch in Twelve Mile Pond has changed such that recruitment is currently more successful since a significant portion of our sample was smaller individuals. The yellow perch fishery in this lake is still excellent, however, as suggested by their proportional stock density (PSD). The lack of abundance of golden shiners and bullheads is due to poor recruitment, directly resulting from heavy predation by the dominant game fish, primarily largemouth bass. Larger groups of small golden shiners were observed in the connecting tributary to the adjacent pond. This nearby water body serves as a refuge for baitfish such as golden shiner, thus sustaining the population. The presence of very large game fish and high predator-prey PSD ratios strongly suggest that Twelve Mile Pond is an under-exploited fishery. The fish population dominated by predatory bass has been able to stabilize from many years of minimal private management, limited fishing pressure, and the catch-and-release ethics of the current land owner. Alewife was not collected in this survey, though they were documented in Trembley s study. It is likely that this species is no longer present in the lake. The implantation of lake

25 chubsucker, as reported by Trembley, as a prey species was presumably unsuccessful. Trembley s recommendation of culling all rock bass in Twelve Mile Pond has been effective, as only 2 large individuals were captured in the entire survey. No trout were captured in the survey, and it is not likely that a population will be established. Dissolved oxygen is reduced below acceptable levels for trout below 5 meters (~16 ft.) in the water column of Twelve Mile Pond. It is recommended that the implemented trout stocking program be ceased and that Twelve Mile Pond be managed as a trophy bass/sunfish fishery. Such management should include removal of all largemouth and smallmouth bass in length. Bass in this size class will eventually create a biological bottleneck, i.e. competition for prey will be stronger resulting in the stunting of the largest predators. REFERENCES Anderson, R.O Proportional stock density (PSD) and relative weight (Wr): interpretive indices for fish populations and communities. Pages in S. Gloss and B. Shupp, editors. Practical fisheries management: more with less in the 1980s. Proceedings of the American Fisheries Society, New York Chapter, Ithaca. Anderson, R.O., and A.S. Weithman The concept of balance for coolwater fish populations. Pages in R.L. Kendall, editor. Selected coolwater fishes of North America. American Fisheries Society. Special Publication 11, Bethesda, Maryland. Ebina, J., T. Tsutsi, and T. Shirai Simultaneous determination of total nitrogen and total phosphorus in water using peroxodisulfate oxidation. Water Res. 17(12): EPA Methods for the analysis of water and wastes. Environmental Monitoring and Support Lab. Office of Research and Development. Cincinnati, OH. Eureka Environmental Engineering Manta water quality probe, startup guide. Austin, TX. Gabelhouse, D.W., Jr A length-categorization system to assess fish stocks. North American Journal of Fisheries Management. 4: Hydrolab Corporation Scout 2 operating manual. Hydrolab Corp. Austin, TX. Kohler, C.C. and W.A. Hubert Inland Fisheries Management in Inland North America. American Fisheries Society, Bethesda, MD. Liao, N Determination of ammonia by flow injection analysis. QuikChem Method J. Lachat Instruments, Loveland, CO.

26 Liao, N. and S. Marten Determination of total phosphorus by flow injection analysis colorimetry (acid persulfate digestion method). QuikChem Method F. Lachat Instruments, Loveland, CO. Pritzlaff, D Determination of nitrate/nitrite in surface and wastewaters by flow injection analysis. QuikChem Method C. Lachat Instruments, Loveland, CO. Trembley, F.J A biological survey of twelve mile pond, Pike County, Pennsylvania. Welschmyer, N.A Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments. Limnol. Oceanogr. 39: