Threadfin Shad Dorosoma Petenense Research Articles

Change in Piscivore Growth Potential after the Introduction of a Nonnative Prey Fish: a Bioenergetics Analysis

AbstractThe introduction of additional forage fish species to enhance sport fisheries is a common management strategy in lakes and reservoirs. However, illegal introductions occur without consideration of all potential ecological consequences. Introduction of Blueback Herring Alosa aestivalis as a forage fish to enhance recreational fisheries has been controversial, with several illegal introductions documented in the southeastern United States. We quantified the caloric density of introduced Blueback Herring and native Threadfin Shad Dorosoma petenense in Lewis Smith Lake, Alabama, to determine their potential values as prey to piscivorous fish. Caloric density estimates were then incorporated into bioenergetics simulations for Largemouth Bass Micropterus salmoides, Alabama Bass Micropterus henshalli, and Striped Bass Morone saxatilis to estimate their growth potential given different diet compositions. Piscivore diet composition from before the introduction of Blueback Herring was also incorporated into bioenergetics simulations for comparison with post‐introduction scenarios. Caloric density of Blueback Herring was higher than that of Threadfin Shad across all seasons, and consequently, bioenergetics simulations predicted increased growth potential for Largemouth Bass, Alabama Bass, and Striped Bass with increased proportions of Blueback Herring in their diets. The simulated growth effect of shifting consumption from Threadfin Shad to Blueback Herring was smaller for Largemouth Bass versus Striped Bass because Striped Bass were far more piscivorous than Largemouth Bass, with Alabama Bass intermediate. Simulated pre‐Blueback Herring piscivore diets resulted in less growth relative to what was observed for all post‐introduction simulations. Although Blueback Herring had higher caloric density values than Threadfin Shad, overall ecological impacts of their introduction are not yet fully understood and could likely also include negative impacts on these piscivores. As such, our findings represent one aspect of the overall, potentially complex effect of introduced Blueback Herring as an additional forage fish for piscivores.

Community Patterns and Environmental Associations for Pelagic Fishes in a Highly Modified Estuary

AbstractUnderstanding how natural and human‐induced processes interact to influence ecosystem responses is essential for their effective management and conservation. Long‐term environmental degradation of the upper San Francisco Estuary, California, has resulted in numerous species declines. In this study, we used pelagic fish monitoring and hydrodynamic data during winter–spring 2002–2014 to evaluate how natural and human‐induced environmental changes in the upper San Francisco Estuary may have influenced the distribution, abundance, and community structure of the pelagic fishes. Delta outflow and turbidity tended to decline and salinity tended to increase since the early 2000s. Twelve of the 27 pelagic fish species sampled were introduced, most of which were freshwater‐dominant species in highly altered upstream areas. Overall mean relative abundance was similar between native and introduced fishes across all study areas. The upstream distribution of the eight most abundant pelagic fishes was generally associated with their salinity habitat components. Among these species, the Delta Smelt Hypomesus transpacificus and the introduced Threadfin Shad Dorosoma petenense had the highest rates of population decline over the period 2002–2014 and the largest relative increase in salinity predicted in their habitats due to hydrological alteration. Community structure was significantly related to abiotic factors (water temperature, salinity, and turbidity) and spatiotemporal variation (longitude and month), which accounted for 30–33% of the variation. Low to intermediate outflows due to droughts and water diversions since the early 2000s likely interacted synergistically with multiple factors, decreasing the abundance of several pelagic species. Management actions linking ecologic, hydrologic, and geomorphic processes with multiple stressors could help to reverse the long‐term decline of Delta Smelt and other threatened and endangered fishes in the San Francisco Estuary.

Pelagic Nekton Abundance and Distribution in the Northern Sacramento–San Joaquin Delta, California

AbstractKnowledge of the habitats occupied by species is fundamental for the development of effective conservation and management actions. The collapse of pelagic fish species in the Sacramento–San Joaquin Delta, California, has triggered a need to better understand factors that drive their distribution and abundance. A study was conducted in summer–fall 2014 in an attempt to identify physical and biological habitat conditions that drive the abundance and distribution of pelagic species in the northern region of the system. The study was conducted in the three largest channels in the northern Sacramento–San Joaquin Delta by dimension, volume, and flow capacity. The pelagic community was dominated by three nonnative species, Siberian prawn Exopalaemon modestus, which comprised 56% of the total number of organisms, and two fish species, Threadfin Shad Dorosoma petenense and Mississippi Silversides Menidia audens, which together comprised 43% of the total number of organisms. Total fish and total shrimp abundance were sensitive to the most extreme values of turbidity and temperature encountered and positively associated with total zooplankton biomass. The results suggested that habitat conditions in terminal channels, historically a common feature on the landscape, support higher abundances of pelagic species and zooplankton than open‐ended channels. These results provide resource managers with useful information on the habitat associations of pelagic species and on how the future distribution and abundance of pelagic species will likely change in response to climate or other ecological factors.Received March 8, 2016; accepted September 22, 2016 Published online December 9, 2016

Importance of Resident and Seasonally Transient Prey to Largemouth Bass in the St. Johns River, Florida

AbstractWe examined seasonal dynamics of prey availability and diets of Largemouth Bass Micropterus salmoides in the St. Johns River, Florida. The four most common prey species were Threadfin Shad Dorosoma petenense, Bay Anchovy Anchoa mitchilli, Atlantic Croaker Micropogonias undulatus, and Atlantic Menhaden Brevoortia tyrannus. The number of prey found in Largemouth Bass varied significantly by month (year‐round) and predator size (“small,” <356 mm TL, n = 267; “medium,” 356–432 mm TL, n = 205; “large,” >432 mm TL, n = 114). Atlantic Menhaden were most energetically beneficial to predators when available. Of the four most common prey species collected in trawls, only menhaden trawl catch was positively correlated with its appearance in bass diets. Menhaden were eaten by bass of all sizes, but were found only from September through November. Largemouth Bass did not feed heavily on juvenile anadromous shads Alosa spp. during their autumn migration, but this likely reflected low abundance of these clupeid species. The seasonal diversity of prey available in the St. Johns River may contribute to its being one of the most productive Largemouth Bass fisheries in Florida.Received June 23, 2014; accepted October 22, 2014

Use of Mini‐Fyke Nets for Sampling Shallow‐Water Fish Communities in Florida Lakes

AbstractWe evaluated mini‐fyke nets for sampling shore‐based (SB; <1 m deep) fish communities in Florida lakes. Specifically, we wanted to determine the most effective deployment method and sample size required for adequately characterizing fish communities in these habitats. Shallow SB (0.15–0.6 m) net sets, in which nets were not completely submersed, collected significantly more individuals and a larger proportion of poeciliids. However, deep SB (0.6–1.0 m) net sets, in which nets were completely submersed, collected a larger proportion of centrarchids, cyprinids, and cyprinidontids. Net placement also significantly affected the overall catch and composition of samples. Nets placed in locations away from the lake boundary tended to collect actively schooling fishes such as Threadfin Shad Dorosoma petenense and cyprinids. Nets placed next to the lake boundary tended to collect species associated with shallow, vegetated habitats, particularly poeciliids, at greater frequencies. In some cases, the collection of these fishes was unique to a particular deployment method. Our results suggest that in long‐term monitoring of Florida's shore‐based lentic fish communities, nets should be placed in SB waters with the lead extending to the lake boundary. Although long‐term sampling objectives may vary, we determined that a sampling target of 30 net sets was sufficient for characterizing the fish community in terms of percentage composition, species richness, and species diversity. Furthermore, we recommend the continued use of additional gears to fully characterize littoral fish communities.Received December 19, 2013; accepted March 1, 2014

Privately Owned Small Impoundments in Central Alabama: A Survey and Evaluation of Management Techniques for Largemouth Bass and Bluegill

AbstractSmall impoundments or ponds represent important fisheries resources, both recreationally and economically. These systems are small relative to most large public reservoirs and natural lakes and thus they are more easily manipulated to improve fishing quality. The utility of some pond management techniques in improving fisheries is not well understood. We combined a telephone survey and field sampling to quantify the characteristics and use(s) of private ponds in central Alabama and determine the efficacy of the most often used pond fishery enhancement techniques. The three most common techniques were fertilization (used by 48% of surveyed pond owners), supplemental feeding with pellets (45%), and the stocking of supplemental prey for largemouth bass Micropterus salmoides (12%; the species most often stocked was threadfin shad Dorosoma petenense). We sampled 66 ponds using boat electrofishing to assess largemouth bass and Lepomis spp. population responses to these management techniques. Fish populations varied greatly within management categories. However, ponds with threadfin shad exhibited overall greater largemouth bass length, length frequency indices (PSD and PSD‐ P, ‐M), growth, body condition, and density than ponds without threadfin shad. Bluegill Lepomis macrochirus population characteristics were similar among all ponds using fertilizer and threadfin shad. Of these techniques, we found that fertilization improved bluegill populations and that threadfin shad can improve largemouth bass populations without compromising bluegill size structure and abundance.Received January 26, 2012; accepted August 7, 2012

Spatiotemporal Distributions of Threadfin Shad in Tropical Reservoirs

AbstractEffective predator management requires accurate knowledge of prey availability and dynamics, yet prey species are rarely studied as intensely as their predatory counterparts. Almost nothing is known about the biology or behavior of threadfin shad Dorosoma petenense in tropical environments, despite that this species is the primary prey in many systems. The goals of this study were to examine spatial and temporal patterns in threadfin shad abundance in tropical reservoirs and to refine protocols for sampling this species. A custom, 3 × 3‐m frame trawl was used to sample four reservoirs in Puerto Rico every 3 months for 1 year. Samples were stratified by longitudinal section (upper and lower lake) and by depth strata (0–3, 3–6, 6–9 m). Threadfin shad densities varied markedly among seasons, reservoirs, longitudinal sections, and depth (overall model: F 36, 188 = 32.0, P < 0.001, coefficient of variation [CV] = 22.1%, r 2 = 0.86). Density estimates from samples were highest in spring and winter when there was substantially more larval production, and density fluctuated as much as 42‐fold among seasons within reservoirs. Differences in mean density were as much as 23 times greater in productive reservoirs than in the least productive reservoir during the same season. Longitudinal variability was substantial between upper and lower reservoir sections (mean percent difference = 70%), but patterns were not consistent among reservoirs or seasons. Threadfin shad showed clear preference for shallow depth strata where 75.4% of fish were collected in the 0–3‐m stratum, and only 2.4% collected in the 6–9‐m stratum. Oxygen profiles suggested that threadfin shad selected shallow depths even when dissolved oxygen levels were suitable in deeper depth strata. Understanding spatiotemporal patterns in threadfin shad distributions will improve sampling programs in terms of timing and frequency of sampling, longitudinal and vertical sampling design, and sample size requirements.Received March 19, 2012; accepted June 2, 2012

Effects of holding temperature and handling stress on the upper thermal tolerance of threadfin shad Dorosoma petenense

The critical thermal maxima (T(MAX)) of threadfin shad Dorosoma petenense exposed to standardized stress (30 s handling in a dip-net), simulating stressors endured during fish loading before transport, were measured over a range of holding temperatures (15, 20 and 25 degrees C). Dorosoma petenense T(MAX) showed a significant thermal effect, displaying mean +/-s.d. critical thermal maxima of 26.5 +/- 1.6, 30.9 +/- 1.2 and 33.3 +/- 1.4 degrees C, when tested at temperatures of 15, 20 and 25 degrees C, respectively. Dorosoma petenense T(MAX) levels were also affected by stress, with handled fish showing significantly lower values than control fish exposed to 15 (mean +/-S.D. T(MAX) = 25.6 +/- 2.0 degrees C), 20 (27.6 +/- 2.8 degrees C) and 25 degrees C (32.0 +/- 2.6 degrees C). In addition to providing basic information on D. petenense thermal tolerance, experimental results suggest that fishery managers should consider the whole suite of potential stressors, such as air exposure during handling and fish loading, when developing management criteria.

Effect of Using Threadfin Shad as Forage for Channel Catfish Fed Daily or Every Third Day

AbstractWe evaluated whether stocking threadfin shad Dorosoma petenense as a forage fish in multiple‐batch production ponds for channel catfish Ictalurus punctatus could substitute for formulated feed when channel catfish were fed daily or every 3 d. A completely randomized design in a 2 × 2 factorial arrangement was used for the experiment, which was conducted in twelve 0.1‐ha earthen ponds. Prespawn adult threadfin shad were stocked at 404 kg/ha in six of the ponds, whereas the remaining ponds received no threadfin shad. Channel catfish stockers (0.35 kg/fish) were stocked at 5,040 kg/ha, and fingerlings (28.2 g/fish) were stocked at 14,820 fish/ha. Channel catfish were fed a floating feed (32% protein) to apparent satiation daily (D; 6 ponds) or every 3 d (3D; 6 ponds). After 144 d, mean channel catfish total net yield was unaffected by the presence of threadfin shad but was significantly greater for fish in the D treatment (7,256 kg/ha) than for fish in the 3D treatment (2,431 kg/ha). Mean fish weight at harvest also was greater in the D treatment than in the 3D treatment. The amount of feed administered in the 3D treatment was 62% of that used in the D treatment, thus reducing net total yield by 66% and slowing growth in fish from the 3D treatment. Nearly 90% of stockers in the 3D treatment failed to reach market size (0.68 kg/fish) and would have required a third season to reach harvest weight. At the rate used in this experiment, stocking of threadfin shad as forage fish into channel catfish production ponds did not appear to be a viable method of substituting for formulated feed during the growing season.

Stocking of Advanced‐Fingerling Largemouth Bass to Supplement Year‐Classes in Lake Talquin, Florida

AbstractSupplemental stocking of largemouth bass Micropterus salmoides has often resulted in limited success in large systems. We evaluated the contribution and relative abundance of advanced‐size (65–90 mm total length [TL]) hatchery Florida largemouth bass M. salmoides floridanus that were stocked into Lake Talquin (3,561 ha) to supplement year‐classes. Stocking density varied from 15 to 60 fish/ha from 2000 to 2003. Coded wire tags and unique nuclei in the sagittal otoliths of hatchery fish were used to identify stocked fish to estimate percent contribution and relative abundance. Hatchery fish released by May 15 used threadfin shad Dorosoma petenense as a primary food source at significantly higher (P < 0.05) frequencies than did wild age‐0 Florida largemouth bass examined from June to October. Dominant modal size‐groups (20–27 cm TL) of age‐0 hatchery fish in October electrofishing were larger than those of age‐0 wild fish (10–14 cm TL). Hatchery fish made up an estimated 17–40% of the age‐0 fish collected during October electrofishing from 2000 to 2003. The highest stocking density (60 fish/ha) resulted in a 40% hatchery contribution to electrofishing samples at age 0 and a 37% contribution to electrofishing samples at age 3. For the group stocked at the highest density, electrofishing catch per unit effort (CPUE) at age 0 (26 fish/h) and age 3 (8 fish/h) was higher (P < 0.05) than that for groups stocked at lower densities (15–39 fish/ha; age‐0 CPUE = 7–17 fish/h; age‐3 CPUE = 2 fish/h). Hatchery fish contribution to largemouth bass angler tournament catch in April–May 2004–2006 was estimated to be at least 20% after 4 years of variable stocking. Several factors, such as appropriate time of stocking, size at stocking, food supply, and age‐0 wild and stocked fish densities, influenced hatchery fish contributions to each year‐class and the fishery.

A Bioenergetics Approach to Modeling Striped Bass and Threadfin Shad Predator‐Prey Dynamics in Lake Powell, Utah‐Arizona

AbstractAn understanding of the mechanisms driving the cyclic relationship between piscivorous sport fish and their food base is needed in systems where predator and prey are tightly coupled. To understand the dynamics between striped bass Morone saxatilis and threadfin shad Dorosoma petenense in Lake Powell, Utah‐Arizona, we (1) synthesized and evaluated 20 years of historical data on temperature, diet, growth, and abundance of these fish, (2) collected similar data on a finer scale in 2003‐2004, (3) used components of this data set to develop specific conversions between coarser historic data and present data, and (4) modeled striped bass and threadfin shad dynamics within a bioenergetics framework. We estimated the consumption of threadfin shad by age‐0, subadult, and adult striped bass in Lake Powell from 1985 to 2003. During this period, threadfin shad abundance peaked at approximately 5‐ to 7‐year intervals and striped bass growth, condition, and abundance corresponded closely to peaks in threadfin shad foraging. Individual consumption of threadfin shad by striped bass was highest for adults followed by subadult and age‐0 fish; scaling individual consumption up to the population level resulted in highly variable subadult consumption that fluctuated from highs of about 1.2 million kg (18.4 kg/ha) to lows of about 0.3 million kg (4.6 kg/ha) on a 1‐ to 2‐year cycle. Despite these fluctuations, the consumption of threadfin shad was dominated by subadult striped bass, which appeared to control threadfin shad numbers in all but the highest peak years of shad abundance. Based on bioenergetics output, striped bass demonstrate a type II functional feeding response; consumption rates reach an asymptote when the threadfin shad biomass index exceeds 10,000 kg/year. We demonstrate a modeling approach that allowed us to evaluate the large fluctuations in predator and prey populations, which often become evident only over long time periods. Our results increase our understanding of the Lake Powell ecosystem and highlight areas for future study.

Effects of Water Velocity and Trash Rack Architecture on Juvenile Fish Passage and Interactions: A Simulation

AbstractMany resident and migratory fish species have experienced population declines due to modification of estuarine ecosystems. Fish screens (or louvers) have been designed to guide fish away from the diversion pumps, and trash racks have been placed upstream of the screens to intercept aquatic plants and debris. Although small fish may aggregate around these structures, potentially increasing their vulnerability to predators, we know little about the behavior, performance, and survival of fish near trash racks. To determine how trash rack flow regime and architecture influence fish behavior, we exposed juvenile threadfin shad Dorosoma petenense and winter‐run Chinook salmon Oncorhynchus tshawytscha to three water velocities and two bar‐spacing treatments in a circular tank bisected by a simulated trash rack. Our results suggest that relatively small increases in water velocity at diversion facilities will result in the aggregation of juvenile fish near trash racks. In contrast, bar spacing did not influence fish passage frequency or interaction in this study. We also found that threadfin shad selected higher velocities as water current increased, whereas Chinook salmon consistently showed a preference for moderate to low water velocities.

Thiamine and Fatty Acid Content of Walleye Tissue from Three Southern U.S. Reservoirs

We determined the thiamine concentration in egg, muscle, and liver tissues of walleyes Sander vitreus and the fatty acid content of walleye eggs from three southern U.S. reservoirs. In two Tennessee reservoirs (Dale Hollow and Center Hill), in which there were alewives Alosa pseudoharengus in the forage base, natural recruitment of walleyes was not occurring; by contrast in Lake James Reservoir, North Carolina, where there were no alewives, the walleye population was sustained via natural recruitment. Female walleye tissues were collected and assayed for thiamine (vitamin B1) and fatty acid content. Thiamine pyrophosphate was found to be the predominant form of thiamine in walleye eggs. In 2000, mean total egg thiamine concentrations were similar among Center Hill, Dale Hollow, and Lake James reservoirs (2.13, 3.14, and 2.77 nmol thiamine/g, respectively). Egg thiamine concentration increased as maternal muscle (r2 = 0.73) and liver (r2 = 0.68) thiamine concentration increased. Walleye egg thiamine does not appear to be connected to poor natural reproduction in Tennessee walleyes. Threadfin shad Dorosoma petenense, which are found in all three reservoirs, had higher thiaminase activity than alewives. Six fatty acids differed among the walleye eggs for the three reservoirs. Two were physiologically important fatty acids, arachidonic acid (20:4[n-6]) and docosahexaenoic acid (22:6[n-3]), which are important eicosanoid precursors involved in the regulation of biological functions, such as immune response and reproduction.

Evaluation of the Ecological Compatibility of Butterfly Peacock Cichlids and Largemouth Bass in Puerto Rico Reservoirs

AbstractIntroduction of peacock cichlids Cichla spp. into tropical and subtropical systems where they can successfully overwinter and reproduce has been a common practice in fisheries management. We evaluated the compatibility of nonnative butterfly peacock cichlids Cichla ocellaris and largemouth bass Micropterus salmoides in Puerto Rico reservoirs using (1) controlled juvenile interaction experiments, (2) examination of hatching periodicity and diet overlap of juveniles in a reservoir environment, and (3) comparison of adult catch data from 10 Puerto Rico reservoirs. In the juvenile interaction experiments, butterfly peacock cichlid juveniles in ponds with largemouth bass had slower growth in length (P = 0.020) and weight (P = 0.003) and lower survival (P = 0.002) than in ponds with only butterfly peacock cichlids. In reservoirs, largemouth bass spawning typically occurred 2–3 months before butterfly peacock cichlid spawning, which resulted in substantial size differences between the juveniles of the two species. Butterfly peacock cichlids fed almost exclusively on threadfin shad Dorosoma petenense; the largemouth bass diet included threadfin shad but was much more diverse. Correlation coefficients were negative for comparisons of adult largemouth bass and butterfly peacock cichlid catch rates in the reservoirs sampled. Pooled catch data from all reservoirs showed a significant inverse relationship in relative abundance (P = 0.026). Catch rates from reservoirs with and without butterfly peacock cichlid populations indicated that largemouth bass densities were higher in single‐predator systems (mean = 85.1/h) than in dual‐predator systems (9.8/h).

Effects of the Extent and Duration of Seasonal Flood Pool Inundation on Recruitment of Threadfin Shad, White Crappies, and Largemouth Bass in Hugo Reservoir, Oklahoma

AbstractOur objective was to determine the effects of the extent and duration of seasonal flooding (meters above normal pool) on recruitment indices for threadfin shad Dorosoma petenense, white crappies Pomoxis annularis, and largemouth bass Micropterus salmoides in Hugo Reservoir, Oklahoma. We used simple linear regression to examine the relations between seasonal pool elevation exceedence duration (number of days for which elevation exceeded target values) and (1) mean monthly (June–September) estimates of age‐0 threadfin shad abundance in midwater trawls; (2) white crappie abundance estimates from May and June trawl samples and November trap‐net samples; and (3) fall electrofishing samples of age‐0 largemouth bass. Due to the large number of relations tested, we could not discount the possibility that a significant positive relation between threadfin shad trawl catches in July–September and winter exceedence duration (≥123.8 m) occurred by chance. No relation was found between elevation and age‐0 white crappie catch in trawls or trap nets. Summer exceedence duration (≥123.8 m) was positively related to largemouth bass recruitment. The results of this study indicated that a water level management plan that calls for holding water in the flood pool during summer would enhance recruitment of largemouth bass in Hugo Reservoir.

Threadfin Shad Dorosoma petenense Effects on Water Quality, Phytoplankton, and Channel Catfish Production in Ponds

AbstractThreadfin shad Dorosoma petenense are often stocked into commercial catfish ponds for biological control of algae. It is thought that the fish will alter the phytoplankton community, improve water quality, and enhance channel catfish production. Co‐stocking of shad and catfish is a common practice, although there is limited information regarding the effects of threadfin shad on pond dynamics and catfish production. To evaluate the influence of shad in catfish ponds, this study was conducted in ten 0.04‐ha experimental earthen ponds near Auburn, Alabama. All ponds were stocked in April with 600 fingerling channel catfish Ictal‐urus punctatus (13,200/ha) with a mean length of 10.4 cm (4.1 in). Additionally, five of these ponds were randomly chosen and stocked with 70 adult threadfin shad (1,750/ha) weighing a total of 3.3 kg (16.5 kg/ha). At harvest in November, an average of 1,284 threadfin shad (32,100/ha), weighing a total of 55 kg (1,375 kg/ha) were collected from each shad pond. Water quality was improved with the addition of threadfin shad to channel catfish ponds. Mean total ammonia‐nitrogen was significantly lower and less variable in the shad treatment. Observed mean nitrite concentrations, though not significant, were lower in the shad treatment. The phytoplankton community of the shad treatment had significantly higher density, more taxa, and smaller organisms. Pond water in the shad treatment had higher projected early morning dissolved oxygen levels requiring less aeration. Channel catfish had significantly higher survival in the shad treatment, furthermore, though not statistically significant, observed mean fish production was higher and feed conversion ratio was lower than in the no‐shad treatment.

Community Responses to Piscivorous Largemouth Bass: A Biomanipulation Experiment

ABSTRACT To test whether piscivorous largemouth bass (Micropterus salmoides) could be used to biomanipulate a 15-ha water supply reservoir, we assessed the effects of the addition of largemouth bass to the reservoir by monitoring the reservoir during the year before and three years after largemouth bass were stocked. A pilot study conducted in October 1990 indicated that the reservoir was eutrophic and contained a fish community dominated by zooplanktivorous threadfin shad (Dorosoma petenense) and no piscivorous fish. The reservoir was monitored during 1991 prior to stocking of largemouth bass (October 1991) and monitored in 1992, 1993 and 1994 after bass were present. Stocking of largemouth bass was successful and bass spawned in 1992, 1993 and 1994. The effects of bass cascaded down through the food web to the phytoplankton. In 1993 and 1994 the number of threadfin shad decreased, the abundance of cladocerans increased and rotifers decreased. Densities of diatoms and green algae were lower in 1992, 1993 and 1994 than in 1991. Although some phytoplankton densities decreased, blue-green algae, chlorophyll biomass, Secchi transparency, total phosphorus and total nitrogen did not change after stocking of largemouth bass and the biomanipulation was not successful in improving the reservoir's water quality.

A Comparison of Diets of Blueback Herring (Alosa aestivalis) and Threadfin Shad (Dorosoma petenense) in a Large Southeastern U.S. Reservoir

ABSTRACT The objective of this study was to determine dietary overlap between blueback herring and threadfin shad in J. Strom Thrumond Reservoir, South Carolina/Georgia. We also evaluated prey selectivity for each speices and diet differences between two size categories of blueback herring. Diet and zooplankton samples were collected every other month from April 1992 to February 1994. We examined stomachs containing prey from 170 large blueback herring (>140mm), 96 small blueback herring (<140mm), and 109 threadfin shad, and we also examined 45 zooplankton samples. Large blueback herring diets differed significantly from threadfin shad diets on 11 of 12 sampling dates, and small blueback herring diets differed from threadfin shad diets on all sampling dates. In general, blueback herring consumed proportionally more copepods and fewer Bosmina sp. and rotifers than threadfin shad. Large and small blueback herring diets were significantly different on five of eight sampling dates, primarily due to the tendency of small blueback herring to eat proportionally more Bosmina sp. than large blueback herring. Both blueback herring and threadfin shad fed selectively during some periods of the year. Diet differences between the species may contribute to their coexistence; however, both blueback herring and threadfin shad showed a strong preference for Bosmina sp., increasing the chance that they may negatively influence one another.

Native and Introduced Larval Fishes of Suisun Marsh, California: The Effects of Freshwater Flow

Abstract We sampled ichthyoplankton weekly in Suisun Marsh in the San Francisco Estuary from February to June each year from 1994 to 1999. We collected approximately 227,900 fish, predominantly shimofuri goby Tridentiger bifasciatus (60%) and prickly sculpin Cottus asper (33%). Principal components analysis and canonical correspondence analysis were used to explore relationships among several environmental variables and the 13 species that made up 99.96% of the catch. A group of native fishes (prickly sculpin, Sacramento sucker Catostomus occidentalis, threespine stickleback Gasterosteus aculeatus, longfin smelt Spirinchus thaleichthys, and Sacramento splittail (also known simply as splittail) Pogonichthys macrolepidotus) were associated with the cool temperatures and higher outflows characterizing early-season conditions in Suisun Marsh. In contrast, a group of introduced species (shimofuri goby, inland silverside Menidia beryllina, striped bass Morone saxatilis, and threadfin shad Dorosoma petenense) we...

Recruitment of Largemouth Bass in Alabama Reservoirs: Relations to Trophic State and Larval Shad Occurrence

Factors affecting recruitment of largemouth bass have frequently been evaluated, but few studies have assessed recruitment potential among a range for reservoirs of varying trophic states. We examined densities of larval threadfin shad Dorosoma petenense and gizzard shad D. cepedianum from Mar to Jul from nine Alabama impoundments. Using shoreline rotenone sampling and daily otolith rings, we estimated density, age, and growth of age-0 largemouth bass Micropterus salmoides in late Jun–Jul. Density and growth of larval gizzard shad, larval threadfin shad, and age-0 largemouth bass increased with chlorophyll a across impoundments. Duration of occurrence for larval gizzard shad and threadfin shad was positively related to chlorophyll a. Eutrophic reservoirs contained larval shad that were 40% or less of mean age-0 largemouth bass total length (i.e., the size at which they would probably be vulnerable to predation) in late Jun–Jul, whereas larval shad were generally not collected in late Jun or Jul in oligo–mesotrophic impoundments. Thus, piscivory on age-0 shad by age-0 largemouth bass was more likely to occur in eutrophic than in oligo–mesotrophic reservoirs. Eutrophic impoundments have high chlorophyll-a values and high larval threadfin shad and gizzard shad densities, and they may provide for greater recruitment of largemouth bass than oligo–mesotrophic impoundments.