Age-0 Largemouth Bass Micropterus Salmoides Research Articles

Hatch timing of largemouth bass: implications for recruitment at the Northern edge of their native range

Climate-related shifts in hatch timing could mean that age-0 largemouth bass Micropterus salmoides in north temperate lakes reach larger sizes and experience higher survival, which may contribute to increased prevalence of this species in many lakes. However, information on age-0 largemouth bass life history is lacking for these lakes. We estimated hatch dates, daily growth rates (DGR), and length-based probability of piscivory of age-0 largemouth bass in Wisconsin lakes to: (1) provide baseline data on early life history; (2) compare hatch timing between years with different spring temperature regimes, and (3) project how shifts in hatch timing might influence total length (TL) distributions of age-0 bass if mean DGR remained constant. Most age-0 largemouth bass (>90%) collected from ten Wisconsin lakes (N = 746) hatched between 23 May and 24 June during 2012 and 2013 and did not switch to piscivory during their first summer. Prevalence of positive correlations (16 of 24 lake-year pairings) between TL in and age indicates hatch timing may influence TLs attained by age-0 largemouth bass in August in some lake-years. Mean daily water temperatures in May 2012 were 3.1 °C warmer than in May 2013 for the five of the six lakes where hatch dates were estimated in both years. On average, earliest and median hatch dates for age-0 largemouth bass in these six lakes were 10–11 d earlier in 2012 than in 2013 and hatch duration was approximately 8 d longer in 2012. Despite differences in hatch timing, mean DGR was relatively consistent (range = 0.61–0.74 mm/d) between lakes and years. Simple simulations suggest that earlier hatch dates could result in more age-0 largemouth bass reaching TLs associated with piscivory and overwinter survival by the end of their first summer if growth rates did not change, which could translate to higher recruitment.

Influence of diet and ambient water on hydrogen and oxygen stable isotope ratios in fish tissue: patterns within and among tissues and relationships with growth rates

The influence of food and ambient water on 2H and 18O isotopic composition in fish soft tissues, how growth affects tissue-specific composition, and relationships of isotope values within and among tissues are poorly known. We exposed age-0 largemouth bass (Micropterus salmoides) to ambient water and food with known δ2H and δ18O values for 65 days and analyzed liver and muscle for δ2H and δ18O levels. Liver δ2H but not δ18O was influenced by water isotopic concentrations and neither ratio was influenced by the isotopic composition of food. In contrast, water and food affected muscle δ2H, whereas muscle δ18O was only influenced by water isotopic values. We observed relationships between fish growth and muscle δ2H and δ18O, where increased growth led muscle to come closer into equilibrium with food and water isotope values, but found no relationships with growth and either liver δ2H or δ18O. Ratios of 2H and 18O were positively related within muscle and within liver of individuals, as were δ2H values between liver and muscle and δ18O values between tissues. Studies assessing 2H and 18O in temperate fishes should account for isotopic contributions from water and food and consider consequences of fish growth and timing of sample collection.

Potential Reservoirs and Risk Factors for VHSV IVb in an Enzootic System: Budd Lake, Michigan.

Viral hemorrhagic septicemia virus genotype IVb (VHSV IVb) has caused major, sporadic fish die-offs in the Laurentian Great Lakes region of North America since 2005. Presently, factors affecting VHSV IVb persistence in enzootic systems are not well understood. Even with annual surveillance, the virus can go undetected for several years after an outbreak before again re-emerging, which suggests that the virus is maintained in the system either below detectable levels or in untested reservoirs. The aim of this study was to identify potential reservoirs of VHSV IVb in Budd Lake, Michigan; VHSV IVb was first detected in Budd Lake in 2007 but remained undetected until 2011. Additionally, we explored the susceptibility of naive fish introduced into a water body enzootic for VHSV IVb by stocking age-0 Largemouth Bass Micropterus salmoides at varying densities into enclosures in the lake. The virus was not detected among samples of the fishes Notropis spp. and Lepomis spp., cylindrical papershell mussels Anodontoides ferussacianus, leeches (subclass Hirudinea), sediment, or water. However, the virus was successfully isolated from amphipods (family Hyalellidae) and Largemouth Bass held in the enclosures. Our finding of VHSV IVb in Hyalellidae amphipods in combination with other research that has detected the virus in Diporeia spp., a large benthic amphipod important as a food resource to Great Lake fishes, suggests that benthic macroinvertebrates are a reservoir for VHSV IVb in infected systems. If there are environmental reservoirs for VHSV IVb in infected systems, they are likely unevenly distributed. Findings of this study add to our understanding of the seemingly complex ecology of this deadly and economically detrimental virus. Received February 22, 2016; accepted October 16, 2016.

Nest Success, Abundance, and Length Distribution of Age-0 Largemouth Bass in Sanctuaries and Areas Open to Fishing

Protecting an area from fishing by establishing a sanctuary is one possible management strategy that could protect adults during spawning, potentially enhancing recruitment in freshwater systems. From 2001-2006, Briery Creek Lake (342 ha), Virginia was characterized by high fishing pressure in spring when adults were spawning and low abundance of age-0 Largemouth BassMicropterus salmoides. Therefore, we created two sanctuaries in 2006 in Briery Creek Lake that were closed to angling and boats; these areas provided protection for nest-guarding male Largemouth Bass. However, the nest-success rate did not differ significantly between open areas and sanctuaries (30-40% nest success). Catch per unit effort of age-0 Largemouth Bass did not differ between areas open to angling (28.8/h and 39.0/h in 2006 and 2007, respectively) and sanctuaries (14.6/h and 22.2/h in 2006 and 2007, respectively). Similarly, mean length-at-capture was not different for age-0 Largemouth Bass between sanctuaries and open areas. Closing spawning areas to fishing may not be an effective management option to increase Largemouth Bass recruitment success in Briery Creek Lake.

Growth-mediated seasonal energy allocation patterns of young-of-year largemouth bass (Micropterus salmoides)

In temperate environments, seasonal selective sources of mortality (e.g., starvation and predation) may drive season-specific energy allocation patterns of young-of-year fish. However, when quantifying such phenomena, the effect of ration is rarely considered. We conducted two experiments to investigate the effect of ration on seasonal energy allocation patterns of age-0 largemouth bass (Micropterus salmoides) during summer and fall. In a laboratory experiment designed to evaluate short-term effects of ration on energy allocation, recent ration history strongly affected body dimensions and length-adjusted energy content. In outdoor raceways, young largemouth bass grew at different rates under different ration levels. In response, length-adjusted energy content, a size-independent index of condition, differed among raceway ration treatments during late summer. However, during fall, high- and low-growth treatment fish expressed similar length-adjusted energy content. Thus, while low-growth fish appeared to allocate a disproportionately low amount of energy to growth of energy-rich storage tissue during late summer, as winter approached, low-growth fish switched and instead allocated a disproportionately high amount of energy to storage tissue. We conclude that energy availability (via ration level) affects short-term energy allocation patterns and may interactively influence seasonal shifts in energy allocation patterns.

Relation of Age-0 Largemouth Bass Abundance to Hydrilla Coverage and Water Level at Lochloosa and Orange Lakes, Florida

Abstract Changes in electrofishing catch per hour (CPH) of age-0 largemouth bass Micropterus salmoides were examined in relation to aquatic macrophytes and seasonal water elevation at Lochloosa and Orange lakes, Florida, during the 1990s. At Lochloosa Lake, stepwise multiple regression revealed a significant positive relationship between the mean CPH of age-0 largemouth bass and the percentage of areal coverage by hydrilla Hydrilla verticallata. At Orange Lake, mean CPH was directly associated with the percentage of areal coverage by hydrilla and inversely related to summer water levels. Thus, the influence of vegetation on age-0 largemouth bass abundance was similar at both lakes, but the effects of water levels were not. Further investigations into the effects of fluctuations in water levels on age-0 largemouth bass in natural lakes are needed.

Evaluation of Injectable Fluorescent Tags for Marking Centrarchid Fishes: Retention Rate and Effects on Vulnerability to Predation

Abstract We evaluated the performance of injectable fluorescent tags for use in mass marking of centrarchid fishes. Using age-0 largemouth bass Micropterus salmoides and bluegills Lepomis macrochirus (50–100 mm total length), we compared (1) the retention rate of injectable photonic dyes (IPDs) applied to the fin rays of largemouth bass, (2) retention rates of IPDs versus visible implant elastomers (VIEs), and (3) the effect of colorless and brightly colored marks on prey selectivity by adult largemouth bass. Retention rate of IPDs declined appreciably in age-0 largemouth bass (50 mm) after 120 d with only 19% of fish retaining visible marks by that time. By the end of the experiment (day 310), no marks were visible in anal fin rays of largemouth bass. For larger age-0 largemouth bass (100 mm), retention rates of IPDs after 48 d were greatest for fish marked in the anal fin (40%), followed by caudal (20%) and dorsal fin (5%) markings. Visible implant elastomers were retained at a higher rate (84.4%) than ...

Evaluating How Local- and Regional-Scale Processes Interact to Regulate Growth of Age-0 Largemouth Bass

Regional- and local-scale processes may interact to influence early growth and survival, thereby governing cohort strength. During summer through fall 1994–1996, we assessed how precipitation (a regional-scale process) and prey availability (a local-scale process) influenced piscivory and growth of age-0 largemouth bass Micropterus salmoides in five Ohio reservoirs (190–1,145 ha). We expected early growth to vary with the abundance and relative sizes of age-0 gizzard shad Dorosoma cepedianum. We collected age-0 largemouth bass and prey fishes every 3 weeks in each reservoir. In 1994, May precipitation was low (total = 4 cm), resulting in low mean daily reservoir discharge (x5 reservoirs = 3.6 m3/s). In four reservoirs, stable water levels may have led to successful largemouth bass reproduction and perhaps an early hatch. As such, age-0 largemouth bass in these systems were abundant, consumed gizzard shad, and reached large sizes by fall (15.3 g). In 1995 and 1996, high precipitation (total > 12 cm) and high reservoir discharge [x5 reservoirs = 13.8 m3/s (1995), 28.8 m3/s (1996)] in some reservoirs in May likely reduced largemouth bass abundances. Growth during these years was density dependent across reservoirs. When age-0 largemouth bass abundance was low, nonshad prey fish were consumed, and mean fall sizes were similar to those in 1994 (12.0 g). Conversely, fall weights (4.5–7.4 g) declined in reservoirs with increasing largemouth bass density. Surveying May precipitation in Ohio across 48 years revealed that conditions like those in 1994 occurred less than 15% of the time. Because gizzard shad should rarely be available and other prey fish species probably are limited, density-dependent processes should often regulate early piscivory, growth, and potentially, cohort strength in these systems.

CLIMATE VARIABILITY AND SIZE-STRUCTURED INTERACTIONS AMONG JUVENILE FISH ALONG A LAKE–STREAM GRADIENT

We examine the influence of biological interactions and interannual variation in climate on the size structure and trophic interactions between age-0 largemouth bass (Micropterus salmoides) and age-0 creek chubs (Semotilus atromaculatus) along a lake–stream gradient in northern Minnesota, USA. Considerable year-to-year variation in temperature and precipitation occurred during the 10-yr study (1983–1992), with most extreme hot-dry conditions in 1988 during a 3-yr drought. Decreased stream temperature and reduced variation in temperature occurred downstream from the lake outlet because of increased groundwater inputs. Age-0 bass were captured in the stream in each of the eight years sampled, but bass abundance peaked in downstream reaches in 1988, concurrent with a large increase in the downstream density of age-0 chubs. Median length ratio of bass to chubs increased greatly in the 1988 drought year. The shift in relative length of bass and chubs during the drought was because chub length decreased in downstream areas, and bass shifted from feeding on invertebrates to feeding on chubs in downstream but not in upstream reaches. Comparison of bass and chub growth in the presence and absence of interspecific competition for invertebrate resources in an experimental stream revealed higher growth rates for chubs than for bass and little interspecific competition. Experiments in the artificial stream indicated that the presence or absence of chubs susceptible to bass predation had only marginal effects on bass survival, but growth rates of bass were substantially higher if chubs susceptible to predation were present. Only when chubs were present was the growth of individual bass dependent strongly on size, and this led to rapid divergence in the size distribution of bass in chubs vs. no-chubs treatments. Our results indicate that hot-dry climatic conditions associated with drought have potentially strong effects on size-structured trophic interactions between age-0 fish along lake–stream gradients. Hot-dry climatic conditions alter the spatial distribution of lake fish along temperature gradients in the stream, the reproductive success and synchrony of lake and stream fish development, and the eventual growth of predatory lake species. The response of fish to climatic variation appears to be strongly influenced by their position in the “hydrologic landscape.” The most dramatic fish response occurred in stream reaches influenced by groundwater.

Influence of Trophic State on Spotted Bass and Largemouth Bass Spawning Time and Age-0 Population Characteristics in Alabama Reservoirs

Abstract We described and compared spawning periodicity, abundance, and growth of age-0 largemouth bass Micropterus salmoides and spotted bass M. punctulatus from six Alabama reservoirs in 1993 and 1994 that displayed a wide range of limnological and morphological characteristics. One reservoir was divided into three distinct areas based on limnological conditions and thus, eight reservoir study areas were examined. Reservoirs fell along a continuum from deep, long-retention reservoirs with fluctuating water levels and low phytoplankton biomass to shallower, short-retention reservoirs with minimum water level fluctuations and generally high phytoplankton biomass. Fish were collected with rotenone in 0.02-ha enclosed shoreline areas. Daily rings on sagittal otoliths were counted to determine growth rates and to back-calculate spawning times. Trophic states included oligotrophic (chlorophyll a, 8 mg/m3; N = 3) sy...

Overwinter Growth and Survival of Largemouth Bass: Interactions among Size, Food, Origin, and Winter Severity

Abstract Winter severity (temperature, duration, and photocycle), geographic origin, food availability, and initial body size likely influence growth, survival, and, therefore, recruitment of age-0 largemouth bass Micropterus salmoides. We collected age-0 largemouth bass (70–160 mm total length) from low (33°N), intermediate (40°N), and high (45°N) latitudes throughout their natural range (origin), and we subjected all three groups of fish to three experimental winters that mimicked these latitudes (N = 9 largemouth bass per treatment). Within each winter and origin, one-half of the largemouth bass were fed fish prey, whereas the remaining one-half were starved. Winter strongly influenced survival; overall survival rates in the high-, intermediate-, and low-latitude winters were 34.9, 59.4, and 61.1%, respectively (χ2 test, P < 0.05). Largemouth bass from 33°N suffered high mortality in the high-latitude winter. Across all winters, more fed fish (64.5%) survived than did starved fish (38.1%) (χ2 test, P <...

Diet Ecology of Yellow Bass, Morone mississippiensis, in an Oxbow of the Mississippi River

ABSTRACT The yellow bass (Morone mississippiensis) is native to the Mississippi River drainage and some adjacent Gulf of Mexico tributaries where it inhabits backwaters, oxbows, and reservoirs. We described the diet ecology of yellow bass in an oxbow of the lower Mississippi River, assessed differences in diets between life stages, and measured diet overlap between yellow bass and coexisting species. Indices of diet breadth differed among age groups, with the diet of age-1 yellow bass being more specialized than that of larger fish. Although the yellow bass consumed a wide array of food items, it tended to rely on certain foods during different life stages. Age-1 yellow bass fed on chironomids, amphipods, and fish eggs, which accounted for 84% of the diet by weight. Age-2+ yellow bass consumed fish, fish eggs, amphipods, and benthic insects, which was over 70% of the diet by weight. Diet overlap was not significant (P > 0.20) between age-1 and age-2+ yellow bass, or between age-1 yellow bass and age-0 largemouth bass (Micropterus salmoides), inland silverside (Menidia beryllina), or juvenile bluegill (Lepomis macrochirus), suggesting that exploitative competition did not occur. Nevertheless, interactions between yellow bass and coexisting species may take the form of intraspecific predation given the propensity of the yellow bass to eat fish eggs.

Physicochemical Influences on Parasites of Age-0 Largemouth Bass in the Atchafalaya River Basin, Louisiana

ABSTRACT We investigated prevalence and intensity patterns of nine parasite taxa in 244 age-0 largemouth bass (Micropterus salmoides) collected from lake (high dissolved oxygen levels), riverine (high current velocities), and swamp (hypoxic canals and bayous) sites (N=6) in the Atchafalaya River Basin during the 1996 flood pulse. Ectoparasites were dominated by monogenetic trematodes (prevalence=100%; median intensities 27–91 per host) and glochidia (prevalence > 96% at all sites, median intensities 47–148 per host), whereas Posthodiplostomum minimum (Trematoda), Caecincola spp. (Trematoda; C. parvulus and perhaps C. latostoma), Neoechinorhynchus cylindratus (Acanthocephala), and Proteocephalus ambloplitis (Cestoda) accounted for 94.6% of bass endoparasites. Overall, lake sites supported the highest median parasite intensities in bass and most highly parasitized individuals. P. minimum was prevalent in bass collected from all sites, but intensities were highest in bass from lake habitats. In contrast, P. ambloplitis exhibited lower than expected prevalence in bass from lake sites (P. < 0.05) and higher intensity (P < 0.02) in bass from riverine sites. Patterns of parasite abundance appeared to be related to habitat effects on intermediate host and parasite life-cycle dynamics rather than hypoxia-related suppression of bass immune responses.

Predicting How Winter Affects Energetics of Age-0 Largemouth Bass: How Do Current Models Fare?

During the first winter of life, loss of energy reserves as a function of low feeding activity and scarce prey may contribute to high mortality of age-0 largemouth bass Micropterus salmoides. To explore how two current bioenergetics models predict winter energy depletion, we quantified growth and consumption by age-0 largemouth bass from Alabama, Ohio, and Wisconsin fed maintenance rations in 55-L aquaria in three simulated winters mimicking temperatures and photoperiods at low temperate latitudes (Alabama; 33°N), middle latitudes (Ohio; 40°N), and high temperate latitudes (Wisconsin; 46°N). We compared observed growth in aquaria with that predicted by putting observed consumption into both models. During winter 1995–1996, we validated one of the models with a separate pool experiment (5,800-L) in which age-0 largemouth bass were fed either at 0.5 × or 1.5 × maintenance ration. In aquaria, energy density of the largemouth bass declined in the high- and middle- but not in the low-latitude winter. Though error was slight in the low- and middle-latitude winters for one of the models, both models underestimated growth in the high-latitude winter. To fit the model to the data, the function that estimates weight-specific resting metabolism had to be reduced by about 16%. In pools, where we predicted consumption from observed growth, the model adequately predicted consumption by largemouth bass fed 1.5 × maintenance, but overestimated consumption by 0.5 × maintenance individuals. Current bioenergetics models perform poorly at the cold temperatures (<6°C), photoperiods, and low prey abundances typical of high-latitude lakes, likely because metabolic costs are overestimated.

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.

Effects of Reservoir Hydrology on Reproduction by Largemouth Bass and Spotted Bass in Normandy Reservoir, Tennessee

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 unimodal in dry years; spotted bass always formed unimodal length-frequency distributions. When largemouth bass exhibited bimodal length distributions, earlier hatched fish grew faster than later hatched fish. Spotted bass grew at similar rates, regardless of hatch date, every year except during 1992 when later hatched fish grew faster than earlier hatched fish. Weekly survival of largemouth bass in their first summer was positively related to reservoir water level. First-year growth of both species was not directly affected by the timing of threadfin shad D. petenense or gizzard shad D. cepedianum hatching.

Linking Bluegill and Gizzard Shad Prey Assemblages to Growth of Age-0 Largemouth Bass in Reservoirs

Either gizzard shad Dorosoma cepedianum or bluegills Lepomis macrochirus dominate prey assemblages in many small (<100 ha) Ohio reservoirs. Because gizzard shad spawn early in the spring and their offspring grow rapidly, age-0 gizzard shad may be invulnerable to age-0 largemouth bass Micropterus salmoides thereby compromising this piscivore's growth and, potentially, recruitment. To test this hypothesis, we quantified growth, abundance, and diets of age-0 largemouth bass in reservoirs dominated by age-0 bluegills (one reservoir) or age-0 gizzard shad (two reservoirs) during June through early October 1992–1994. In the bluegill-dominated reservoir, age-0 largemouth bass grew slowly (about 0.04 g/d) during June through mid-August. Though age-0 bluegills became abundant after mid-August, contributing to rapid growth (about 0.2 g/d) of age-0 largemouth bass, these age-0 largemouth bass only reached small to moderate sizes by fall (range of mean wet weights, 3–7 g). In the reservoirs dominated by gizzard shad, summer growth and fall sizes of largemouth bass varied among systems and years. During one summer in one shad-dominated reservoir, an early rise in temperature plus small age-0 gizzard shad probably contributed to rapid growth (∼0.12 g/d) and large fall size (mean wet weight, 10.8 g) of age-0 largemouth bass. More commonly, age-0 largemouth bass grew slowly or moderately (∼0.06 g/d). However, fall sizes of largemouth bass always were equivalent to or exceeded those in the bluegill-dominated reservoir (range of mean wet weights, 3–11 g). Our results suggest that growth of age-0 largemouth bass should vary more in systems dominated by gizzard shad than in bluegill-dominated ones. Management efforts that increase gizzard shad vulnerability during early summer may reduce this variability, thereby enhancing first-summer growth and, potentially, recruitment success of largemouth bass.

Spatial Heterogeneity in Abundance of Age-0 Largemouth Bass among Reservoir Embayments

Abstract Abundances of age-0 largemouth bass Micropterus salmoides in reservoirs usually are assessed on an annual, lakewide basis. This scale obscures patterns that may be important in explaining variations in abundance. We hypothesized that abundances of age-0 largemouth bass differ consistently among reservoir embayments and that among-embayment variation might exceed annual variation. We collected age-0 largemouth bass annually from four embayments of B. Everett Jordan Lake, North Carolina, from 1989 to 1995. Two of the embayments consistently exhibited higher abundances. Variation in abundances among embayments averaged 4.2-fold from lowest to highest, compared to a 2. I -fold variation in lakewide abundances among years. Significant differences in abundances among years occurred only in the bays where abundances were low, and they were not associated with annual differences in reservoir water levels. Recognizing the existence of significant among-embayment differences in age-0 largemouth bass abunda...

Morphological Constraints on Intracohort Cannibalism in Age-0 Largemouth Bass

Abstract Intracohort cannibalism can be an important process shaping the growth and survival of age-0 largemouth bass Micropterus salmoides. To assess the morphological constraints on Intracohort cannibalism in largemouth bass, we evaluated the relationship of mouth width, body depth, and total length in age-0 fish. Morphological measurements predicted a threshold predator-prey relationship of: prey length = 0.309·predator length1.109, whereas experimental results suggested the relationship of: prey length = 0.5·predator length. Our results indicated that Intracohort cannibalism may begin as early as 9 d after swim-up in southern lakes and reservoirs and 12 d in northern lakes. However, because of the length of the spawning season, slower growth, and male guarding, Intracohort cannibalism may be more important in southern systems than in northern lakes.

Winter Survival of Age-0 Largemouth Bass Relative to Size, Predators, and Shelter

Abstract Winter mortality of age-0 largemouth bass Micropterus salmoides is sometimes size dependent, with smaller fish experiencing higher mortality. We conducted this study to determine if the presence of predators influenced winter mortality of young largemouth bass, if predators influenced all sizes of young equally, and if increased shelter availability moderated a possible relation between predator-induced mortality and fish size, We stocked 0.06-ha experimental ponds with largemouth bass (30 fish/pond) of five length groups (55–100, 101–125, 126–150, 151–175, and 176–200 mm total length), with and without predators (three largemouth bass 250–350 mm long), and four levels of shelter (0, 10, 16, and 26% brush coverage of surface area of ponds). In ponds without shelter, survival ranged from 10 to 97% in the presence of predators and from 77 to 93% in the absence of predators. Fish less than 126 mm long had gradually lower survival in the presence of predators, but near 80% survival in the absence of ...