R. Scott Hale

NUTRIENT CYCLING BY FISH SUPPORTS RELATIVELY MORE PRIMARY PRODUCTION AS LAKE PRODUCTIVITY INCREASES

Animals can be important in nutrient cycling in particular ecosystems, but few studies have examined how this importance varies along environmental gradients. In this study we quantified the nutrient cycling role of an abundant detritivorous fish species, the gizzard shad (Dorosoma cepedianum), in reservoir ecosystems along a gradient of ecosystem productivity. Gizzard shad feed mostly on sediment detritus and excrete sediment-derived nutrients into the water column, thereby mediating a cross-habitat translocation of nutrients to phytoplankton. We quantified nitrogen and phosphorus cycling (excretion) rates of gizzard shad, as well as nutrient demand by phytoplankton, in seven lakes over a four-year period (16 lake-years). The lakes span a gradient of watershed land use (the relative amounts of land used for agriculture vs. forest) and productivity. As the watersheds of these lakes became increasingly dominated by agricultural land, primary production rates, lake trophic state indicators (total phosphorus and chlorophyll concentrations), and nutrient flux through gizzard shad populations all increased. Nutrient cycling by gizzard shad supported a substantial proportion of primary production in these ecosystems, and this proportion increased as watershed agriculture (and ecosystem productivity) increased. In the four productive lakes with agricultural watersheds (>78% agricultural land), gizzard shad supported on average 51% of phytoplankton primary production (range 27-67%). In contrast, in the three relatively unproductive lakes in forested or mixed-land-use watersheds (>47% forest, <52% agricultural land), gizzard shad supported 18% of primary production (range 14-23%). Thus, along a gradient of forested to agricultural landscapes, both watershed nutrient inputs and nutrient translocation by gizzard shad increase, but our data indicate that the importance of nutrient translocation by gizzard shad increases more rapidly. Our results therefore support the hypothesis that watersheds and gizzard shad jointly regulate primary production in reservoir ecosystems.

Retention and Detection of Coded Wire Tags and Elastomer Tags in Trout

Abstract Tag retention rates above 95% and easy tag detection were possible with blank coded wire tags and elastomer tags implanted in a variety of body locations of adult trout (Salmo and Oncorhynchus spp.). These tags were used in a generic way to differentiate 6 groups of brown trout Salmo trutta (142–254 mm total length, TL) and 26 groups of rainbow trout Oncorhynchus mykiss (80–314 mm TL) that were stocked at different times and locations in the Cumberland River, Kentucky. Retention rates (19–30 d) ranged from 92% to 100% for coded wire tags implanted in the snout, left cheek, and muscle near the left pectoral, pelvic, dorsal, adipose, and caudal fins. Retention rates (24–30 d) ranged from 94% to 99% for elastomer tags placed in the left and right adipose eyelids and the caudal fin rays. Loss of coded wire tags by trout did not increase with the number of days tagged fish were held in raceways, which suggested that most tag loss had occurred before stocking. By contrast, loss of elastomer tags increa...

Evaluation of a 254-mm Minimum Length Limit on Crappies in Delaware Reservoir, Ohio

Abstract A 254-mm minimum length limit on black crappies Pomoxis nigromaculatus and white crappies P. annularus was evaluated during a 6-year trial (1991–1996) at Delaware Reservoir, Ohio. The primary objective of the length limit was to increase the size of crappies harvested without substantially reducing yield. Mean length at harvest increased up to 66 mm following implementation of the length limit. However, a 78% average decrease in total annual harvest was too great to compensate for the larger size at harvest and to compensate for annual yield (kg) reductions of 38–76% while the regulation was in effect. Annual catch-and-release rates of crappies at Delaware Reservoir increased from 35–43% to 84–97% and became the greatest in Ohio. Likewise, Delaware Reservoir had greater angler catch per effort and mean size at harvest compared with unregulated crappie fisheries in Ohio. Both crappie species maintained preregulation growth rates despite modest density increases of sublegal fish, whereas relative w...

Seasonal Consumptive Demand and Prey Use by Stocked Saugeyes in Ohio Reservoirs

Abstract Community structure and species composition may be strongly influenced by predator– prey interactions resulting from and leading to episodes of population abundance or scarcity. We quantified diets of stocked saugeyes (female walleye Sander vitreus × male sauger S. canadensis) and estimated biomass of their primary prey, gizzard shad Dorosoma cepedianum, in three Ohio reservoirs at quarterly intervals during July 2002–July 2003 to determine whether saugeye consumptive demand could exceed the supply of available gizzard shad prey, resulting in a shift to alternative prey. We incorporated water temperature and saugeye diet composition, growth, and mortality into walleye bioenergetics models, which allowed us to compare estimated prey-specific consumption rates by saugeyes with gizzard shad standing stocks estimated with acoustics. Spring and summer were critical seasons. During spring, gizzard shad biomass was low, saugeye consumptive demand was low, and saugeyes consumed primarily alternative prey...

Predicting Crappie Recruitment in Ohio Reservoirs with Spawning Stock Size, Larval Density, and Chlorophyll Concentrations

Abstract Stock–recruit models typically use only spawning stock size as a predictor of recruitment to a fishery. In this paper, however, we used spawning stock size as well as larval density and key environmental variables to predict recruitment of white crappies Pomoxis annularis and black crappies P. nigromaculatus, a genus notorious for variable recruitment. We sampled adults and recruits from 11 Ohio reservoirs and larvae from 9 reservoirs during 1998–2001. We sampled chlorophyll as an index of reservoir productivity and obtained daily estimates of water elevation to determine the impact of hydrology on recruitment. Akaikes information criterion (AIC) revealed that Ricker and Beverton–Holt stock–recruit models that included chlorophyll best explained the variation in larval density and age-2 recruits. Specifically, spawning stock catch per effort (CPE) and chlorophyll explained 63–64% of the variation in larval density. In turn, larval density and chlorophyll explained 43–49% of the variation in age-...

Differential Growth of Young-of-Year Gizzard Shad in Several Kentucky Reservoirs

Abstract Protracted spawning of gizzard shad Dorosoma cepedianumwas not responsible for the small juvenile shad collected during the fall in two Kentucky reservoirs and one hatchery pond. Gonadosomatic indices of female gizzard shad at Taylorsville Lake and the number of gizzard shad 10 mm and smaller collected in four study lakes did not increase following a mid-July water-level rise. Large numbers of small gizzard shad were collected during the fall at Cave Run and Taylorsville lakes and in one of the hatchery ponds even though spawning was not detected after the normal period. As a result, fall length-frequency distributions of juvenile gizzard shad differed among study lakes and among hatchery ponds. Our data indicated differential and density-dependent growth of young-of-year gizzard shad occurred in the reservoirs and hatchery ponds, and suggested that managers could increase availability of forage by developing techniques to manipulate shad densities.

Catch Comparisons of Surface Sampling Methods for Age-0 Gizzard and Threadfin Shad

Abstract Catches in neuston nets were used to estimate abundance and size structure of shad Dorosoma spp. Neuston net catches also were compared with catches in 0.5- and 1.0-m-diameter towed nets and in paired 0.5-m-diameter push nets. At Guist Creek Lake, Kentucky, all sampling methods showed similar abundance trends of gizzard shad D. cepedianum. Catch per unit effort was lower for neuston nets than for 1-m nets but not significantly different from those of other nets through late June. At B. Everett Jordan Lake, North Carolina, neuston and 1-m nets gave similar abundance estimates of Dorosoma spp. on three of five sampling dates; catches in the 1m net were significant higher on two dates. Precision of abundance estimates was higher at B. Everett Jordan Lake than at Guist Creek Lake, where precision decreased through the sampling season. Mean lengths of shad differed among sampling methods and between tows with the same net, but these differences were rarely large. Neuston, 1-m, and push nets captured g...

Growth of White Crappies in Response to Temperature and Dissolved Oxygen Conditions in a Kentucky Reservoir

Abstract Abiotic factors that may regulate growth, recruitment, and mortality of warmwater fishes in reservoirs of the Midwest and southeast United States are poorly understood. I examined the effect of reservoir temperature on the growth of white crappies Pomoxis annularis in a Kentucky reservoir to test the hypothesis that warm summer epilimnion temperatures may constrain white crappie growth and describe annual patterns of seasonal growth. Each year reservoir stratification reduced epilimnion volume as summer progressed and prevented white crappie use of cooler hypolimnetic waters due to low dissolved oxygen conditions below the thermocline. Water temperature at the 3-m depth explained significant portions of variability in growth of both juvenile (age-1) and adult (age-2) white crappies during 1989–1993. Higher temperatures resulted in slower instantaneous growth rates, and growth usually decreased during Jul and Aug. Seasonal growth rates differed between juvenile and adult white crappies. Juveniles ...

Development and Evaluation of a Bioenergetics Model for Saugeye

Abstract We parameterized and evaluated a bioenergetics model for saugeye (walleye Sander vitreus × sauger S. canadensis) by using laboratory experiments in an effort to improve predictions of prey consumption. First, we measured daily prey consumption rate and growth of age-0 and age-1 saugeyes fed two daily rations (ad libitum and 50% of maximum) at five temperatures ranging from 10°C to 28°C. Additional experiments quantified routine respiration rates and waste losses for three ages of saugeye (ages 0, 1, and 2) at five temperatures ranging from 10°C to 28°C. Mean daily rates of prey consumption (g·g−1·d−1) by saugeyes increased from 10°C to 25°C, declining at 28°C. Respiration rates (g O2·g−1·d−1) increased over the entire range of water temperatures. Waste losses were minor for saugeyes as egestion averaged 3.5% of consumed energy and energy lost via excretion was 4.5% of assimilated energy. We evaluated the accuracy of bioenergetics model predictions of saugeye prey consumption using daily prey cons...

Paddlefish as Potential Acoustic Targets for Abundance Estimates

Abstract Underwater acoustics is a noninvasive sampling technique that potentially reduces expense and injury to target species, but this method may be underutilized for sampling large freshwater fishes. We measured target strength (TS), developed anatomically based backscatter models, and conducted gill-net and acoustic surveys of paddlefish Polyodon spathula to explore the potential use of acoustic surveys for estimating the abundance of large freshwater fishes. Mean TS measured from two size-groups of paddlefish at 200 kHz was −37.14 decibels (dB; SD = −2.36) for age-0 fish (353–406 mm) and −27.25 dB (SD = −2.21) for adult fish (1,018–1,284 mm), indicating that TS could differentiate these size-groups. Backscatter models identified strong contributions of the swim bladder to TS and revealed the sensitivity of acoustic backscatter to paddlefish length, aspect, and acoustic carrier frequency. Model results were generally within one SD of measured means from individual fish of each size-group. Target stre...