Phillip W. Bettoli

Use of a Split-Plot Analysis of Variance Design for Repeated-Measures Fishery Data

Abstract We present a repeated-measures split-plot analysis of variance (ANOVA) design that can be used to analyze fisheries data collected throughout time from fixed sampling stations. A high percentage (97%) of authors who published papers in the Transactions of the American Fisheries Society and the North American Journal of Fisheries Management during the past 10 years did not use repeated-measures ANOVA for analyzing their data when this technique was appropriate. When data are collected from fixed stations throughout time, the assumption that independent samples are randomly collected from the population is violated for simple ANOVA. Fixed stations may display population characteristics specific to that location, and environmental change or a management practice may influence stations differently. In addition, multiple measurements collected at a fixed station throughout time will likely be correlated. For a dependent variable of interest, a repeated-measures split-plot design will partition the var...

Piscivory in Largemouth Bass as a Function of Aquatic Vegetation Abundance

Abstract The incidence of predation by largemouth bass Micropterus salmoides on fish in Lake Conroe, Texas, was examined over 7 years at two disparate levels of habitat complexity. When areal coverage of submersed vegetation ranged from 39 to 44% of the reservoirs 8,100 hectares, largemouth bass 100 mm and smaller in total length consumed fish infrequently; most did not consume fish until they reached lengths of 140 mm and more, Following the elimination of all submersed vegetation by grass carp Ctenopharyngodon idella, fish were consumed by most largemouth bass 60 mm or longer. The initiation of piscivory at smaller sizes resulted in significantly faster first-year growth for all largemouth bass year-classes produced after vegetation removal. Although shifts in the structure of the forage fish community occurred, ample fish prey existed for largemouth bass before and after vegetation removal. The onset of piscivory remained similar for largemouth bass collected along the dam riprap, where vegetation was...

Response of a Reservoir Fish Community to Aquatic Vegetation Removal

Abstract Over 3,600 hectares of submersed aquatic vegetation in Lake Conroe, Texas, were eliminated 1 year after 270,000 grass carp Ctenopharyngodon idella were stocked in 1981–1982. Seventeen fish species were commonly collected in cove rotenone samples and the biomasses of eight species declined (P ≤ 0.10) after vegetation removal. The most notable declines were observed for several small, phytophilic Lepomis spp., for bluegill Lepomis macrochirus, and for crappie Pomoxis spp. Biomass of largemouth bass Micropterus salmoides did not decline (P = 0. 12) but the density of age-1 and older fish did decline (P = 0.02). Biomass and density of two cyprinid species and channel catfish Ictalurus punctatus increased. Although biomass of longear sunfish Lepomis megalotis did not increase (P = 0.11), mean size declined and density increased an order of magnitude (P = 0.02). Density of threadfin shad Dorosoma petenense increased nearly fivefold after vegetation removal, coincident with a decline in mean size; howev...

Larval Sampling as a Fisheries Management Tool: Early Detection of Year-Class Strength

Abstract Larvae of black crappies Pomoxis nigromaculatus, white crappies P. annularis, and white bass Morone chrysops were sampled in 1992–1996 from Normandy Reservoir, Tennessee, with a 1 × 2-m neuston net. Larval crappies were not captured in 1992 or 1993, but densities over the remaining three years varied over two orders of magnitude. Larval white bass were collected every year, but densities also varied over two orders of magnitude among years. Larval crappies recruited to the gear at 9 mm total length (TL), but few over 15 mm were collected. Larval white bass recruited to the gear at 7 mm TL and continued to be sampled by the neuston net at lengths up to 35 mm TL. Peak larval crappie density in the neuston net samples was an accurate predictor of geometric mean number of age-1 crappies per hectare 1 year later in midsummer cove samples (r 2 = 0.99, P = 0.0001). Peak white bass density in the neuston net samples was an accurate predictor of geometric mean catch of age-0 white bass in fall gill-net sa...

Hooking Mortality and Behavior of Striped Bass Following Catch and Release Angling

Abstract Concerns over the use of minimum-size regulations to increase the average weight of harvested striped bass Morone saxatilis in Tims Ford Reservoir, Tennessee, prompted this study of hooking mortality. To estimate mortality and examine behavior, striped bass longer than 508 mm total length were caught with conventional angling gear, tagged externally with ultrasonic transmitters equipped with floats, and released back into Tims Ford Reservoir. Over a 15-month period 89 fish were tagged and tracked for a minimum of 3 d. Mortality rates ranged from 14% in November and December 1993 to 67% in both August 1993 and July 1994. Although the confounding effects of tagging could not be separated from the effects of being hooked and released, disparate mortality rates among seasons, as well as observations of feeding and swimming behavior of tagged fish that survived, suggested that tagging effects were modest compared to hooking effects. Mortality rates were linearly related to air temperature (P = 0.012) ...

Variation in Largemouth Bass Recruitment in Four Mainstream Impoundments of the Tennessee River

Abstract Variation in recruitment of largemouth bass Micropterus salmoides was quantified in four mainstream impoundments along an 800-km segment of the Tennessee River and compared with various types of hydrologic and aquatic plant abundance data in an attempt to explain factors related to the formation of strong and weak year-classes. Residuals from four catch-curve regressions for age-2–11 fish collected in 1993 or 1994 were used to describe year-class strength. The formation of strong and weak year-classes was generally synchronous in these four reservoirs. Year-class strength was inversely related to average June–July discharge and positively associated with retention (reservoir volume/discharge) for data pooled from all reservoirs. Thus, weak year-classes were produced during wet early-summer conditions after largemouth bass hatched, whereas stronger year-classes were produced during dryer early-summer conditions. Late-summer aquatic plant abundance and water level fluctuations during April–May whil...

Movement of saugers in the lower Tennessee River determined by radio telemetry, and implications for management

Abstract Since 1979, abundances of sauger Stizostedion canadense have declined in the Tennessee River system. Reasons for this decline may include overharvest, loss of spawning habitat, and low recruitment due to extreme flows. The purpose of this study was to investigate the movements of saugers following winter concentration below Pickwick Dam, Tennessee. Thirty-seven saugers were implanted with radio transmitters directly below Pickwick Dam and were tracked between December 1992 and June 1993. Four saugers moved upstream through the locks at Pickwick Dam: the remaining fish stayed within the first 30 km of the tailwater throughout the spawning season. Three areas below Pickwick Dam were identified as possible March prespawn staging sites. After April 1, saugers in the tailwater area began a rapid downstream migration to the main basin of Kentucky Lake. Some fish moved downstream more than 200 km in less than 10 d in this semiclosed system. Movements encompassed four states (Kentucky, Tennessee, Mississ...

Effects of reservoir hydrology on reproduction by largemouth bass and spotted bass in Normandy Reservoir, Tennessee

Abstract Age-0 largemouth bass Micropterus salmoides and spotted bass M. punctulatus were collected from Normandy Reservoir, Tennessee, 1992–1996, to evaluate effects of reservoir hydrology and hatching of shad Dorosoma spp. on hatching and first-year growth and survival of these two species. Fish were collected in cove rotenone samples in early Aug and electrofishing samples biweekly throughout the summer; hatch dates and age-specific growth for both species were determined from cove samples with sagittal otoliths. Hatching of both species ranged from early April to early Jun. Initiation of largemouth bass spawning, but not spotted bass spawning, was positively related to the first day water levels achieved full pool. Mean hatch dates of both species were positively related to the first day of full pool. Timing of spawning for both species was not related to water temperature. Largemouth bass exhibited bimodal length-frequency distributions by midsummer in two wet years and length frequencies were unimod...

Fate, Dispersal, and Persistence of Recently Stocked and Resident Rainbow Trout in a Tennessee Tailwater

Abstract A popular trout fishery in the Clinch River below Norris Dam, Tennessee, is maintained by an extensive stocking program. However, survival and return rates of rainbow trout Oncorhynchus mykiss stocked as catchables are low. Twenty rainbow trout (mean total length (TL) = 307 mm) that had resided in the tailwater at least 5 months were collected from the river and implanted with radio transmitters in June 1998. Similarly sized rainbow trout were implanted with radio transmitters at a hatchery and stocked into the Clinch River on 8 July 1998 (N = 19; mean TL = 304 mm) and 16 September 1998 (N = 11; mean TL = 311 mm). The stocked rainbow trout dispersed rapidly and nearly all (93%) of those fish died quickly or emigrated from the tailrace. Resident fish were significantly less active than stocked fish, and they persisted significantly longer (Kruskal–Wallis tests, P = 0.0001). Poor return rates and survival of rainbow trout stocked as catchables were attributed to their rapid, long-range movements an...

Population Dynamics of a Reservoir Sport Fish Community in Response to Hydrology

Abstract Sport fish from Normandy Reservoir, Tennessee, were sampled for more than 6 years with a variety of gears targeting different life stages. Normandy Reservoir experienced different hydrologic regimes over the sampling period that we roughly grouped into dry years (1992 and 1995), intermediate years (1993 and 1997), and wet years (1994 and 1996). Year-class strength of largemouth bass Micropterus salmoides was fixed each year by late summer or early fall. Catch of age-1 largemouth bass in spring electrofishing samples was directly related to the number of days the reservoir was at or over full pool when the fish were age 0. Largemouth bass produced in a wet year and intermediate year were more than twice as abundant at age 3 than fish produced in two dry years. Recruitment of spotted bass M. punctulatus could not be linked to reservoir hydrology. Crappies Pomoxis spp., white bass Morone chrysops, and saugeyes (walleye Stizostedion vitreum × sauger S. canadense) produced poor year-classes in dry yea...