In addition to monitoring sportfish communities through annual surveys, TWRA sponsor's research aimed at answering specific questions about our fisheries management. Recent reservoir studies have investigated factors affecting sportfish spawning and survival, competition potential, stocking success, and evaluated harvest restrictions. Some studies are conducted in-house, but most studies are contracted to universities where students are able to use the data to obtain graduate degrees in fisheries science. Results are often published in some of the most prestigious journals of the fisheries profession.
- Statewide Sauger Recruitment Study (TN Tech Univ. 1998)
Factors Associated with Recruitment of Saugers in Tennessee and Cumberland River Reservoirs, Tennessee, 1990-1997
Important seasonal fisheries exist for indigenous saugers Stizostedion canadense in the mainstream impoundments of the Tennessee and Cumberland Rivers, Tennessee; however, extreme fluctuations in abundance of sauger populations result in cyclical fisheries. Experimental gill nets were used to collect sauger over eight years in four Tennessee River reservoirs (Watts Bar, Chickamauga, Guntersville, and Kentucky) and one Cumberland River reservoir (Old Hickory) during spawning migrations (January - April). Between 1990 and 1997, 634 saugers were collected from the Cumberland River and 3,179 were collected from the Tennessee River. Saugers ranged from age-1 to age-10; however, 97% of the saugers were less than age-4. Due to the absence of older saugers, all fisheries were dominated by saugers less than 400 mm TL. Age- 1 and age-2 sauger catches were used as indices of recruitment in the Tennessee River and Cumberland River, respectively. Sauger recruitment was modeled as a function of the amount of water discharged and number of fingerlings stocked in previous years. Sauger recruitment in two upper Tennessee River reservoirs was related to total volumes discharged the previous spring (February to April; r>+0.91; P=0.0001); no significant relationship between spring discharges and recruitment was evident in two lower Tennessee River reservoirs or Old Hickory Reservoir on the Cumberland River. Current models suggest that February-April discharges between 8.4 x 109 and 15.4 x 109 m3 may enhance recruitment in the Tennessee River; whereas, discharges above or below this range are detrimental. Optimal discharges cannot occur simultaneously throughout the Tennessee River. Based on empirical relationships between discharge, recruitment, and river reaches, we concluded that strong recruitment throughout the Tennessee River cannot occur in the same year. Recruitment was not related to fingerling stockings in two upper Tennessee River reservoirs; however, age-2 sauger catches in Old Hickory Reservoir on the Cumberland River were related to the number of fingerlings stocked two years earlier (r=+0.99; P=0.0001). Gonadosomatic index values were either zero for immature or spent male and female saugers, or >0.075 and >0.025 for mature female and male saugers, respectively. Total length (TL) at maturity for female and male saugers was approximately 300-325 mm TL and 225-250 mm TL, respectively. The 381-mm minimum size limit in the upper Tennessee and Cumberland River protected 73-85% and 32-52% of mature male and female saugers, respectively. The 356-mm minimum size limit in the lower Tennessee River protected 78% and 47% of the mature male and female saugers, respectively. Saugers collected in the upper Tennessee River were significantly older and longer, on average, than saugers collected from the lower Tennessee River in most years. The pooled average age of saugers in the Tennessee River over their eight-year study was 1.99 years. We propose that mean ages falling outside the range of 1.5 to 2.5 years (+2 S.D) will characterize populations suffering from over-exploitation or consistently poor recruitment.
- Normandy Water Level Study (TN Tech Univ. 1998)
Influence of Water Levels and Habitat Manipulations on Fish Recruitment in Normandy Reservoir
Spring water levels account for much of the variation seen in spawning success of fishes in Normandy Reservoir. The years of 1992, 1993, and 1995 and 1997 were characterized by the following:
- low spring water levels, often not attaining full pool until April 30
- low crappie, white bass, and gizzard shad reproduction
- delayed spawning by largemouth bass and threadfin shad
- slow growth rates, poor survival, and lower abundance of young-of year largemouth bass
In contrast, spring water levels in 1994 and 1996 exceeded full pool as early as March 27, remained at or above full pool most of the spring, and fish dynamics were characterized by the following:
- high crappie, white bass, and gizzard shad reproduction
- natural reproduction by saugeyes
- earlier initiation and longer duration of largemouth bass and threadfin shad
- spawning periods
- formation of a bimodal length-distribution of fast-growing young-of-year
- largemouth bass
- high survival rates and abundance of young-of-year largemouth bass
The Normandy Project has examined many different aspects of the fish community in the reservoir. Other pertinent findings of this project include:
- Electrophoretic analysis of Stizostedion spp. confirmed that stocked saugeyes were reproducing in Normandy Reservoir, both with other saugeyes and with walleyes. Reproduction of saugeyes in Normandy Reservoir has compromised the genetic integrity of walleyes in the reservoir, placed downstream parental stocks at risk, and precluded the control of Stizostedion population densities.
- Year-class strength of largemouth bass was fixed in late summer every year.
- Neuston net sampling of larval fishes was effective in predicting subsequent year-class strength of crappies and white bass. This sampling method could allow managers to determine when poor year classes of these species are produced and take appropriate remedial action.
- Spotted bass and largemouth bass were spatially segregated in Normandy Reservoir. Young-of-year largemouth bass were usually more abundant in the lower basin; young-of-year spotted bass were more evenly distributed. Catch of age-1 and older largemouth bass was highest in an embayment off the lower basin; age-1 and older spotted bass were more abundant in the upper basin.
- Catch rates of adult largemouth bass and smallmouth bass were highest in riprap and lowest in gravel habitats in both spring and fall samples, and fish were smaller in gravel habitats in both seasons. Spring catch rates of spotted bass varied unpredictably among five habitats, but fall catch rates of this species were highest in rubble habitats and lowest in cove and mixed substrate habitats. Catch rates of largemouth bass and spotted bass were lower in fall than spring; however, catch rates of smallmouth bass were higher in fall than spring. Managers designing electrofishing surveys to obtain a random sample of black bass should be aware that electrofishing catch rates vary according to specific habitat preferences of both size and species of black bass.
- The dynamics of spotted bass populations in reservoirs are poorly-understood and little studied. A critical period for spotted bass was not observed and we could not determine when year-class strength was fixed. Efforts to understand this species are warranted, because they are an important sport fish species in Tennessee reservoirs. Since 1991, spotted bass have represented as much as 40% of the total black bass catch and 60% of the black bass harvest from Normandy Reservoir.
- Production of larvae by threadfin shad and gizzard shad varied over two orders of magnitude and was inversely related to adult threadfin shad abundance. Winterkills of threadfin shad were size selective, killing all fish under 60 mm TL but allowing some unknown percentage of larger fish to survive. When threadfin shad stocks were reduced by winterkills, surviving threadfin shad and gizzard shad may have taken advantage of less competition for food resources in early spring and increased condition enough to spawn successfully.
We initiated the habitat manipulation phase of the study in 1995. Three types of habitat improvement structures (cypress tree plantings, furring strips, and brush piles) were constructed and use of these structures by littoral fishes, including black basses, was evaluated during the summers of 1995 and 1996. Mean catch of juvenile largemouth bass and spotted bass did not differ between habitat-improvement sites and unmodified sites either year. We found little beneficial effect of habitat enhancement structures in Normandy Reservoir. Habitat enhancement is costly, time-consuming effort, and appears to offer little promise of enhancing year-class strength of black basses in Tennessee reservoirs. To construct a total of fifteen 50-m sections of brushpiles, furring strips, and cedar tree habitats on Normandy Reservoir, we spent approximately $1200, or roughly $80 per 50-m of habitat. Any increase in black bass year-class strength via habitat enhancement would probably be outweighed by the typical increase observed in a high- water year. Trying to duplicate the positive effects of high water using artificial habitat enhancement would involve changing the habitat in virtually the entire reservoir, which would be prohibitively expensive. Attempts to enhance year-class strength of fishes in Tennessee tributary impoundments should focus on altering the hydraulics of systems and not shoreline habitat.
- Norris Lake Striped Bass Study (Mississippi State Univ. 1999)
The goal of this study was to assess if predation by striped bass on game fishes, forage fishes, or both are limiting populations of game fishes in Norris and Watts Bar reservoirs. Specific objectives were (1) to identify the extent and effect of predation by striped bass on gamefish populations, (2) evaluate the potential for competition for prey resources among gamefish populations in the reservoirs, and (3) compare extent of competitive interactions between these two reservoirs that have different productivity levels. The study lasted from 1 October, 1996, through 30 September, 1998. Early in the study (February 1997) we identified complications that invalidated comparison of competitive interactions between the reservoirs. Thus, after consultation with TWRA, Watts Bar Reservoir was excluded from study, sampling escalated at Norris Reservoir, and objective 3 was voided. Consequently, most of the information reported herein pertains to Norris Reservoir, although summaries of data collected during the five-month sampling period at Watts Bar Reservoir are provided.
At Norris Reservoir during 1 October, 1996, and 30 September, 1997, we collected 1,136 striped bass (279-1,105 mm TL), 92 smallmouth bass (109-515 mm), 168 spotted bass (114-348 mm), 592 largemouth bass (95-592 mm), 237 black crappie (146-356 mm), 1,573 walleye (255-681 mm), 109 sauger (266-522 mm), 106 channel catfish (159-763 mm), and 34 flathead catfish (405- 875 mm). At Watts Bar Reservoir during 1 October, 1996 and 28 February, 1997 we collected 93 striped bass (194-960 mm), 80 hybrid striped bass (417-790 mm), 52 smallmouth bass (115- 549 mm TL), 76 largemouth bass (127-572 mm), 60 white crappie (220-390 mm), 367 sauger (247-508 mm), and 6 walleye (313 to 654 mm).
Striped Bass Predation on Game Fishes
The first objective was to estimate the total consumption of game fishes by striped bass over a 1- year period using a bioenergetics model, and to determine whether this level of consumption resulted in gamefish biomass reductions greater than those acceptable to resource users. The net influence of predation on a population is equal to the amount consumed less what would have been lost to other sources of mortality (i.e., compensatory mortality responses). Therefore, to properly evaluate the significance of predation, estimates of gamefish removal by striped bass were coupled with analyses of compensatory mortalities of the game fishes. The potential for the population to display a compensatory response is a function of their mortality-density relationship. If natural mortality is density-dependent and increases with density for a gamefish species, then their consumption by striped bass may have been mitigated. In other words, because of striped bass predation, other sources of mortality (e.g., cannibalism, consumption by other predators, starvation, disease), may be reduced resulting in no net change or even an increase in population size. Because predation on game fishes may vary annually, and our 1-year sampling period could not capture is variability, we simulated various levels of predation by striped bass and their effect on game fish density by modeling increases in the percentage of game fishes in striped bass diet.
The only game fishes consumed by striped bass were lepomids, ranging in total length from 53 to 203 mm. Overall, consumption of lepomids was relatively low, accounting for 4% (34.334 kg) of the 899,274 kg consumed, and 6% of the total biomass of lepomids in the reservoir. Although lepomids were eaten by striped bass and several other predators, black basses were eaten only by other black basses. By weight, black basses represented 9% of the diet of largemouth bass, 3% for smallmouth bass, and 14% for spotted bass.
Mortality-density relationships for the species considered were compensatory, indicating that decreased population abundance leads to increased survival. Given this relation, observed predation by striped bass on lepomids was not found to be harmful to the lepomid populations. Correspondingly, modeling predicted that if striped bass consumption of game fishes were to increase, black basses would have to make up 4-9% of the striped bass diet, and black crappie nearly 25%, before harmful effects would occur.
Potential for Competition
Our second objective was to evaluate the potential for competition for prey among selected predators in Norris Reservoir. Competition is difficult to measure, and likely varies seasonally and annually depending on availability of food resources and changes in habitat utilization. Thus, our approach aimed at evaluating whether the conditions for intense competition existed, rather than actually measuring the extent of competition.
Two species may be able to share an abundant food resource without competing, but competition occurs only when the shared resource is in short supply. Therefore, in this second objective we estimated (1) diet overlap to assess if the prey supply was being shared, and (2) prey supply to assess if it was limiting. Substantial overlap would not confirm the presence of competition, but only the possibility for existence; however, finding no or limited overlap would indicate that substantial competition was unlikely. A supply-demand analysis was conducted to assess if forage deficiencies existed. By comparing supply versus demand, a ratio was developed to evaluate food resource sufficiency.
Collectively, the targeted predator populations in Norris Reservoir consumed an estimated 5.6 million kg of prey. On an annual basis, total consumption and clupeid consumption for all examined predator populations combined averaged 403 and 290 kg/ha, respectively. The majority of prey consumed (72%) consisted of clupeids. Of the clupeids identified to the genus level, 77% were Dorosoma spp. and 23% alewife.
The striped bass population consumed nearly 0.9 million kg of prey annually; 95% of the prey consumed were clupeids. Consumption by striped bass accounting for 16 and 21% of the total prey and total clupeids consumed by the targeted predator populations, respectively. Of the clupeids identified to the genus level, 67% were Dorosoma spp. and 335 alewife.
Diet overlap between striped bass and other species ranged from 0.04 to 0.99 (0 = no overlap, 1 = full overlap), and varied seasonally. Significant overlap occurred with all species, but not in all seasons. These results indicated that exploitative competition between striped bass and coexisting game fishes is plausible if the prey-supply-to-predator-demand ratio is low.
Clupeid biomass available to predators averaged 558 kg/ha and annual production 687 kg/ha. For a total annual supply of 1,245 kg/ha. Most of the clupeid supply (86%) was centered on fish ages 0 and 1. Biomass of lepomids averaged 36 kg/ha and production 34 kg/ha, for a total annual supply of 70 kg/ha. Total prey supply (clupeids + lepomids) averaged 1,315 kg/ha.
Collectively, the targeted predator populations in Norris Reservoir consumed a total of 290 kg/ha of clupeids and 32 kg/ha of lepomids. Of the total demand for clupeids, black crappie accounted for 31%, striped bass 21%, walleye 18%, smallmouth bass 15%, largemouth bass 12%, spotted bass 3%, and sauger 1%. Age 0 clupeids represented 92% of the total demand for clupeids and 83% of the total prey demand. Of the total demand for lepomids, largemouth bass accounted for 39%, smallmouth bass 27%, walleye 15%, spotted bass 11%, striped bass 7%, and sauger 1%.
The supply-demand ratio averaged 3.5. Given simulated fluctuations in both supply and demand from 0.25 to 2 times that of the mean, supply-demand ratios ranged from 0.44 to 28.2. Supply- demand ratios less than 1, and probably less than 2, are unsustainable and perhaps uncommon, although not unlikely. It is difficult to associate a supply-demand ratio to competition without additional information on the minimum ratio necessary to sustain predator demand, but given the potential range of supply-demand ratios, it is likely that the level of competition for prey among game fishes in Norris Reservoirs varies annually and can become intense in some years.
We predicted that supply-demand ratios would increase by as much as 25% if striped bass were removed and stocking was discontinued. Such removal would increase prey supply by an estimated average 64 kg/ha. This surplus would increase biomass of native game fishes by as much as 13 kg/ha, or about 20%, if foraging efficiency of native predators is 1.0 (i.e., all prey eaten by striped bass can be captured by other game fishes). Nevertheless, foraging efficiency is likely to be less than 100%; thus, smaller increases should be expected. Our best guess, based on a 25% foraging efficiency in Norris Reservoir, is that biomass of other game fishes would increase by an average 5-10% if striped bass are removed.
- Statewide Crappie Population Studies (Tennessee Tech Univ. 2000)
Indexing Year-Class Strength of Crappies Using Larval Sampling in Tennessee Reservoirs
Larval crappies were sampled from three reservoirs (Douglas, Region IV; Percy Priest, Region II; Barkley, Region 1) in 1998 and 1999 to determine if year-class strength could be predicted from larval densities. All samples were taken by towing a 1 x 2 m neuston net weekly at 14 to 16 sites per reservoir. All samples were conducted at night except for Barkley Reservoir, where the same 14 sites were sampled during the day and night to examine diel differences in catch. Catch of crappie larvae in neuston samples reflected catch of age-0 crappies collected in fall trapnetting samples only in Douglas Reservoir. Lack of a precise measure of year-class strength in Percy Priest Reservoir did not allow similar comparisons in that system. However, larval crappie catches in 1999 (a dry spring) were half that in 1998 (a wet spring); similar patterns have been documented in other Tennessee reservoirs. Catch of crappie larvae was low in both day and night samples in Barkley Reservoir in both years, despite high catches of age-0 crappies in fall trapnets in 1999. It appears that neuston net sampling, developed on Normandy Reservoir in the mid-90s, has application in tributary storage impoundments across the state, and could be a useful tool for fisheries managers desiring to index year-class strength of crappies. However, use of this method in mainstem impoundments like Barkley Reservoir may be limited.
Year-Class Contribution By, Post-Stocking Survival of, and Predation on Stocked Black-Nosed Crappies in Tennessee Reservoirs
The Tennessee Wildlife Resources Agency currently stocks approximately one million crappies annually; however, a systematic evaluation of this program has not been conducted. We assessed year-class contribution, initial post-stocking mortality, and predation upon recently stocked crappies in seven Tennessee impoundments. An oxytetracycline (OTC) marking technique was used to assess the year-class contribution of stock crappies in three large Tennessee reservoirs and one small impoundment. Marking efficacy ranged from 97-100% and marks persisted for at least 80 weeks. Crappies marked and stocked in Normandy Reservoir during October-December 1997 represented 90% of age-1 fish collected in August 1998 retenone samples and 70% of the age-2 crappies collected in a 1999 spring electrofishing sample. Initial post-stocking survival was assessed by placing fish in net pens for approximately 24 hours. Post-stocking mortality rates ranged from 0-95%, averaged 16%, and were most heavily influenced by loading time and hauling density. Predation on recently-stocked crappies was evaluated by stomach analysis of potentially predacious fish collected by electrofishing 100-m transects proximal to stocking sites. Occurrence of stocked crappies in predator stomachs ranged from 14 to 41% among five systems; predation rates could be high in systems with high densities of predators such as Woods Reservoir and Lake Graham. Stocked BNC were on average 30% smaller than wild age-0 black crappies and 40% smaller than wild age-0 white crappies collected from eight reservoirs at roughly the same time the BNC were stocked, which may increase their risk of predation. Adding to this risk is the fact that the fish are often stocked in late fall, which is a time when major prey species such as shad are offshore and inshore prey density is low. By changing seasons or life stages when crappies are stocked, managers may make this program more widely successful, and benefit the crappie fisheries of more reservoirs in Tennessee.
Evaluation of the Statewide 254-MM Minimum Length Limit on Crappies in Tennessee Reservoirs
We evaluated the effect of harvest restrictions on the crappie fisheries in 12 large Tennessee reservoirs. A Beverton-Holt equilibrium yield model was used to predict and compare the response of these fisheries to three size restrictions: the current 254-mm total length limit, a 229- mm limit and a 178-mm limit (i.e., no size limit). The predicted responses of crappie fisheries to size-limits differed among reservoirs and varied with rates of conditional natural mortality (CM). In general, Tennessee Reservoirs fell into one of three groups. In the first group (Normandy, Woods, Chickamauga, Cherokee, and Douglas Reservoirs), a 254-mm size restriction would benefit the fishery if CM was low (30%) and may not harm the fishery if CM was close to 40%. However, at a CM of 50%, yield was adversely impacted by size restrictions, and the decrease in number harvested was severe enough to overcome improvements to the size structure of the population. In the second group (Barkley, Kentucky, J. Percy Priest, Dale Hollow, Watts Bar, and Norris Reservoirs), size limits would provide benefits if CM was low (30%). However, when CM was higher, decreases in the number harvested under a size restriction would probably outweigh any benefits gained by improving the size structure of the population. In any case, a 229-mm size restriction would be better on these lakes than the current 254-mm restriction. The last group, consisting only of Tellico Reservoir, showed no benefits to yield or size structure of the population under any size restriction at any level of CM. Mean number harvested also decrease under all size restriction scenarios. In Tellico Reservoir, the fishery would be best managed with no size limit.
The main factor affecting the response of crappie populations to size limits was growth. With the exception of Cherokee and J. Percy Priest Reservoirs, populations that recruited to the 254-mm size limit in under three years (Normandy, Woods, Chickamauga, and Douglas Reservoirs) appeared to benefit from the size limit under low and intermediate levels of CM. Populations that recruited to the 254-mm size limit in three or four years (Barkley, Kentucky, Dale Hollow, Watts Bar, and Norris Reservoirs) appeared to be better served by the 229-mm limit under low and intermediate levels of CM. With the except of Barkley Reservoir, these populations recruited to the 229-mm limit in less than three years. In Tellico Reservoir, fish did not recruit to the 254-mm size limit until 4.5 years of age, and no size restriction appeared to benefit the population. The use of a statewide length limit to regulate crappie harvest assumes that crappie population dynamics are similar among the major of regulated waters and that the response of these fisheries to such a regulation would be fairly homogenous among systems. Our findings indicate that site- specific regulations may provide more effective management strategies. Based on model results, the response of Tennessee reservoir crappie fisheries to size and exploitation rates determined the exact response of the population to different size restrictions. Accurate estimates of conditional natural mortality and exploitation rates for crappies in Tennessee reservoirs are lacking and are essential to improve model applicability.
Effects of Hydrology on Recruitment of Crappies in Tennessee Reservoirs
Black crappies and white crappies were sampled to index recruitment in eight reservoirs (four mainstems, four tributary storage impoundments) across the state of Tennessee. Crappie recruitment variation in two reservoirs was estimated from historical catch of age-0 fish in fall trapnet samples. In the remaining six reservoirs, variation in recruitment was assessed by examining residuals generated from catch curves. Mean daily discharge and reservoir storage volume values were obtained for each reservoir for three time periods each year: pre-spawn (1 January to 31 March), spawning (1 April to 31 May) and summer (1 June to 30 September). A combined model for three of four tributary storage impoundments revealed a strong positive relationship between year-class strength and discharge in the pre-spawn period. Discharge data were not available for the fourth tributary impoundment; however, year-class strength was negatively related to storage volume of the reservoir in the pre-spawn period. Crappie recruitment in the four mainstem impoundments was highest at intermediate levels of discharge, and a weak inverse relationship existed between crappie recruitment and mean daily discharge during the spawning period. No other relations were found between crappie recruitment and other hydrological variables in any reservoir. Crappie recruitment was linked to reservoir hydrology; however, the critical time and nature of the relationship (positive or negative) differed between tributary storage impoundments and mainstem impoundments. Thus, it is likely that crappie populations will rarely have strong year classes simultaneously over a wide geographic area, or even within a single watershed.
Age, Growth, Mortality, and Species Composition of Crappies Populations in Tennessee Reservoirs, and Difficulties in Sampling Them
Population characteristics of crappies were examined from twelve Tennessee reservoirs sampled either in spring or fall with either trapnets or electrofishing. Total annual mortality (A) was estimated in eight of the twelve study reservoirs; high recruitment variability prevented estimation of A in four reservoirs. Total annual mortality ranged from 54-75% and averaged 66%. Total annual mortality was not correlated to mean length at age-3 among reservoirs sampled in the fall. Total annual mortality from age-2 to age-5 for black crappies ranged from 52-79% and averaged 64%; total annual mortality for white crappies ranged from 35-68% and averaged 54%. The distributions of lengths at age-3 were variable across reservoirs in terms of range and skewness, often encompassing the entire length range seen for the whole sample. Most of the variability in growth among reservoirs sampled during the fall was explained by an inverse relationship with chlorophyll-a concentrations. Mean relative weights of both species were not related to mean length at age-3 in reservoirs sampled during the fall. Species composition varied greatly among reservoirs, from systems dominated by black crappies (e.g., Dale Hollow, Cherokee, Chickamauga) to systems dominated by white crappies (e.g., Tellico, Percy Priest, Woods). Based on mean lengths at age-3, black crappies grew slower than white crappies in Barkley, Chickamauga, Kentucky, Normandy, and Woods Reservoirs; no significant differences in growth between species were detected in Douglas and Watts Bar Reservoirs. The percentage of black crappies in each reservoir was negatively correlated with chlorophyll-a concentrations.
Crappie species compositions in concomitant electrofishing and trapnet samples were relatively similar in Kentucky and Barkley Reservoirs. However, in Woods Reservoir black crappies and black-nosed crappies represented 63% of the trapnet sample but only 38% of the electrofishing sample. Similarly, black crappies represented 81% and 91% of the catch in trapnet samples from Normandy Reservoir in 1996 and 1997, respectively, but only 46% and 41% in spring angling samples taken concurrently. Species compositions in Normandy electrofishing samples taken at roughly the same time of year in subsequent years resembled those of the angling samples in 1996 and 1997. More white crappies were caught in the headwaters and fewer in the lower reaches of Douglas Reservoir; black crappie catch rates were similar among areas. More white crappies were caught in the headwater reaches of Kentucky Reservoir than in the middle and lower reaches. Catch rates of black crappies were higher in the lower and headwater reaches than in the middle reach of Kentucky Reservoir. Length-frequencies of crappies collected in concomitant electrofishing and trapnet samples in Kentucky and Barkley Reservoirs were distinctly different; electrofishing collected larger fish than trapnets in both systems.
We feel that the best sampling regime for assessing crappie populations in Tennessee reservoirs would be to use trapnets only to index year-class strength, coupled with concurrent electrofishing in the fall to collect larger individuals for age and growth analyses. All mainstem reservoirs can be sampled in this way, and some tributary impoundments may also fall into this category. In systems where fall larval sampling is ineffective (e.g., most tributary storage impoundments), we suggest that larval sampling be used to index year-class strength and spring electrofishing be used to obtain age and growth data.
Spatial and Diel Variation in Distribution of Limnetic Larvae of Fishes in Two Tennessee Reservoirs
Larvae were sampled over six years from Normandy Reservoir, a 1,307-ha tributary storage impoundment and over two years from Barkley Reservoir, a 23,458-ha mainstem impoundment in Tennessee. Larvae were collected from 16 sites stratified over 4 areas in Normandy Reservoir and 14 sites stratified over embayment and main channel habitats in Barkley Reservoir. Sites were sampled both day and night in Barkley Reservoir; sites were sampled only at night in Normandy Reservoir. In Barkley Reservoir, suckers and cyprinids were always more abundant in the main river channel than in embayments. In contrast, shad Dorosoma spp., silversides, longperch Percina caprodes, and sunfish Lepomis spp. were usually more abundant in embayments. Larval fish distribution patterns in Normandy Reservoir were generally more homogenous. Larval distribution patterns in Barkley Reservoir resembled that of large rivers and were consistent with spawning requirements for each group, and were likely a reflection of spawning habitats used by adults. Embayments provided important habitats for many fish species at the spawning and larvae stages. Main river channel habitats supported fewer species of larvae, but appeared to be an important spawning area for native suckers and cyprinids. Catches of larval fish in Barkley Reservoir were usually higher at night than during the day for all groups of larval fish; however, variation did occur among groups, years and study areas. Stratifying samples among habitats is essential to accurately assess larval fish communities in large systems such as Barkley Reservoir, but is less important in systems such as Normandy Reservoir, with a more homogenous distribution of larvae. However, both types of systems should be sampled at night to maximize the number of individuals and taxa collected.
- Statewide Walleye Recruitment Study (Tennessee Tech Univ. 2001)
Evaluation of Current Management Practices and Assessment of Recruitment, Growth and Condition of Walleyes in Tennessee Reservoirs.
Tennessee's walleye stocking program was evaluated by releasing fry and fingerlings marked with oxytetracycline (OTC). Marking efficacy was high (>99%) for walleyes immersed in 500 mg/L OTC for 6 hours and mortality was negligible. Subsequent recaptures of age-1 walleyes revealed that little or no natural reproduction occurred in 1999 and 2000 in the five study reservoirs (Center Hill, Norris, South Holston, Tellico, Watauga). The contribution of stocked walleyes to those two year classes ranged between 92 and 100%.
Adult walleyes were sampled with experimental gill nets in six reservoirs (the five mentioned above and Dale Hollow). The oldest walleyes (up to age-21) were in Watauga Reservoir; the youngest population was in Center Hill Reservoir, where only one fish was older than age-4. The age-class structure in the six reservoirs indicated that most of the walleye fisheries were dependent on TWRA's stocking program because natural reproduction was usually low or inconsistent over the last decade.
Trout stocking rates and threadfin shad catch rates together explained a significant amount of variation in adult walleye robustness. The heaviest walleyes were in South Holston, Dale Hollow and Watauga Reservoirs. Significant between-year variation was also detected for four of the six populations sampled.
No threadfin shad were collected in Watauga Reservoir, but they were caught in similar numbers in the other five reservoirs. Alewives were in all six reservoirs and their catch rates varied significantly; mean catch rates were higher in Watauga and Dale Hollow (207-300/net night) than in the other four reservoirs (7-23/net night).
Walleyes grew rapidly in all reservoirs; the average time to reach 406-mm total length ranged from 1.7 to 2.1 years.
Fishery yields under different minimum size limits were simulated using the Beverton-Holt equilibrium yield model. Three size limits (381-, 406-, and 457-mm total length) increased yield in all reservoir compared to no size limit at most levels of exploitation when conditional natural mortality rates were low (less than 20%). At higher natural mortality rates, the benefits of a minimum size limit were eliminated. The observed longevity of walleyes (maximum age averaged 13 years over all reservoirs) indicated that natural mortality rates were low; thus, minimum size limits were appropriate management actions in all reservoirs. Although yield was usually highest under simulated 457-mm length limit, the benefits were slight unless conditional fishing mortality rates were high (>40%) and natural mortality rates were low (10%).
Only one walleye population (Center Hill) exhibited characteristics of heavy exploitation. Although most populations were sustained through a stocking program, the abundance and size structure of most populations was excellent. Large variations among reservoirs in walleye robustness and forage abundance suggested that stocking rates should be matched to the supply of available forage.