Age-0 Fish Research Articles

Evaluation of Trophic Niche Overlap between Native Fishes and Young-of-the-Year Common Carp

Common carp Cyprinus carpio is a ubiquitous invasive species that commonly imposes negative effects on aquatic ecosystems. However, research evaluating the effects of carp on native fishes is limited. Carp are highly fecund and larvae and juveniles can be abundant. If age-0 carp use similar prey resources as native fishes, they may compete if food becomes limited. We used traditional diet analysis for samples during Jul. and Aug. 2008 in Brant Lake. Stable isotopes were used for samples collected during Aug. and Sep. 2009 in Brant Lake and Lake Sinai to examine prey resource use by age-0 carp and four native fishes: bluegill Lepomis macrochirus, black crappie Pomoxis nigromaculatus, yellow perch Perca flavescens, and orangespotted sunfish Lepomis humilis. Age-0 carp were generally as or more abundant than native fishes. In Jul. Daphnia dominated the diets of all fishes sampled, resulting in high (>60%) dietary overlap ranging from 87–98%. In Aug. Daphnia density in Brant Lake declined and dominant diet prey types shifted for carp (to Trichoptera and Daphnia), yellow perch (to Amphipoda), and the three Centrarchids (to Cyclops and Diaptomus). This diet shift resulted in lower diet overlap between Centrarchids and either carp (<40%) or yellow perch (3–16%) but high diet overlap within Centrarchids (67–97%). Stable isotope analysis further indicated greater resource overlap when most fishes relied on zooplankton and lesser overlap as fishes shifted to benthic prey. Our results suggest that resource competition between age-0 carp and native fishes is most likely to occur during early summer if Daphnia availability becomes limited but becomes less likely as dominant prey in diets increasingly diverge among fish species over time.

Patterns of age-0 yellow perch growth, diets, and mortality in Saginaw Bay, Lake Huron

Identifying mechanisms influencing early-life survival may elucidate recruitment variability of fish populations. Yellow perch (Perca flavescens), are economically and ecologically important in Saginaw Bay, Lake Huron, but have recently experienced low recruitment despite strong production of age-0 fish. Recent year classes have been characterized by slow first-year growth, as indexed by fall size of age-0 yellow perch; however, seasonal growth patterns and accompanying diet and survivorship patterns have not been documented for age-0 yellow perch in Saginaw Bay. To this end, we collected age-0 yellow perch weekly (larvae) and monthly (juveniles) throughout the first year of life during 2009 and 2010 to track changes in growth and diet composition. We also evaluated predation and over-winter energy-loss as potential mechanisms of size-selective mortality. Yellow perch growth, energy accumulation and size-specific condition decreased during late summer and fall. During larval and juvenile stages, predominant components of yellow perch diets transitioned from copepods to Daphnia and other zooplankton; however, we observed only weak ontogenetic shifts toward benthic prey. Smaller yellow perch a) were preferentially preyed upon by walleye (the bay's main piscivore) and b) displayed lower mass-specific energy content, potentially increasing overwinter starvation risk, suggesting that slow growth increases mortality risk. Our results are consistent with the hypothesis that recruitment dynamics are influenced by an interplay of size-selective mortality and diet-induced reductions in growth.

Energy content of young yellow perch and walleye in Saginaw Bay

We evaluated seasonal energy content of age-0 yellow perch Perca flavescens and walleye Sander vitreus in Saginaw Bay, Lake Huron in 2009 and 2010. We also determined the energy content of age-1 fish from the 2009 and 2010 cohorts the following spring (i.e., for fish that had survived one winter) to evaluate overwinter energy losses. As expected, larger fish within each species had disproportionately higher energy content (i.e., slope relating length and energy >3.0) than smaller conspecifics. By contrast to expectations, allometric slopes were >3.0 in nearly all months, not just the fall, and were higher for age-0 yellow perch than for walleye, even though increased allocation to growth would have seemingly been beneficial to even the largest yellow perch during summer. Seasonal energy allocation patterns differed between years. In 2009, length specific energy content increased from late summer to fall for both species. However, for the 2010 cohorts of fish, length specific energy content decreased between late summer and fall for yellow perch and did not change for walleye. There were 13–17% overwinter declines in length specific energy content between the fall (October or November) and the spring (May) with no major differences between cohorts within a species or between species for a given year. Because young yellow perch and walleye are similar physiologically but differ in size (i.e., yellow perch are smaller), it is possible that overwinter energy losses are more important for yellow perch than for walleye.

Chaos and stability of age-0 fish assemblages in a temperate deep reservoir: unpredictable success and stable habitat use

Large year-to-year variability in different fish species recruitment has been confirmed by previous studies while diurnal patterns of occupation in two basic reservoir habitats (pelagic and littoral) by different age-0 fish species in late summer are still unclear. Data collected over an 11-year period regarding late-summer age-0 fish assemblages in pelagic and littoral habitats of a reservoir were used to test the recruitment instability and to investigate diurnal habitat use. Trawling was conducted in the pelagic habitat at night while beach seining was conducted in the littoral habitat during day and night. Fluctuations in age-0 fish abundance and species composition were observed with both sampling methods; however, the following spatio-temporal patterns were relatively stable in most investigated years: (1) pelagic species (pikeperch; Sander lucioperca, small perch; Perca fluviatilis, bream; Abramis brama at night), (2) littoral species (large perch, asp; Leuciscus aspius, dace; Leuciscus leuciscus), (3) migratory species likely performing diel horizontal migrations (bleak; Alburnus alburnus), (4) species abundant in the littoral habitat both during day and night and also in pelagic habitat at night (roach; Rutilus rutilus) and (5) species detected in both habitats exclusively at night (ruffe; Gymnocephalus cernuus).

Overwinter Mortality of Sympatric Juvenile Bluegill and Yellow Perch in Mid-Temperate Sandhill lakes, Nebraska, U.S.A

Substantial mortality can occur in age-0 fish populations during their first year of life, especially in winter; this can potentially influence overall recruitment into the adult population. As such, we compared relative abundances between fall and spring catches of sympatric juvenile bluegill Lepomis macrochirus Rafinesque and yellow perch Perca flavescens (Mitchill) to evaluate the magnitude of overwinter mortality across locations (five lakes for two years) and through time (one lake for six years). In addition, we compared both quantile-quantile and increment plots, based on length-frequency histograms from fall- and spring-caught cohorts from 2004 to 2010, to determine if mortality was sizeselective while accounting for over winter growth. Bluegill relative abundances (as indexed by catch-per-unit-effort) significantly decreased from fall to spring, although size-selective mortality was not detected in 10 instances. Yellow perch relative abundances were similar from fall to spring in five Nebraska Sandhill lakes; however, size-selective mortality was detected, with size-selective over winter mortality of smaller individuals occurring in one of eight instances, whereas greater mortality in larger individuals occurred in two instances. Positive growth occurred in both species but was variable among lakes and appeared to be system-specific. In Nebraska Sandhill lakes, over winter mortality likely differs between these two species in its severity, size-selective effect, and scale (i.e., lake-specific vs. large-scale processes), and is likely influenced by combinations of these (and potentially other) factors.

Diet and habitat use by age-0 deepwater sculpins in northern Lake Huron, Michigan and the Detroit River

Deepwater sculpins (Myoxocephalus thompsonii) are an important link in deepwater benthic foodwebs of the Great Lakes. Little information exists about deepwater sculpin spawning habits and early life history ecology due to difficulty in sampling deep offshore habitats. Larval and age-0 deepwater sculpins collected in northern Lake Huron and the Detroit River during 2007 were used to improve our understanding of their habitat use, diet, age, and growth. Peak larval density reached 8.4/1000m3 in the Detroit River during April and was higher than that in Lake Huron. Offshore bottom trawls at DeTour and Hammond Bay first collected benthic age-0 deepwater sculpins in early September when fish were ≥25mm TL. Otolith analysis revealed that hatch dates for pelagic larvae occurred during late March and larvae remained pelagic for 40 to 60days. Diet of pelagic larvae (10–21mm TL) was dominated by calanoid copepods at all sample locations. Diets of benthic age-0 fish varied by location and depth: Mysis and chironomids were prevalent in fish from Hammond Bay and the 91m site at DeTour, but only chironomids were found in fish from the 37m DeTour site. This work showed that nearshore epilimnetic sites were important for pelagic larvae and an ontogenetic shift from pelagic planktivore to benthivore occurred at about 25mm TL in late summer. Age analysis showed that larvae remained pelagic long enough to be transported through the St. Clair–Detroit River system, Lake Erie, and the Niagara River, potentially contributing to populations in Lake Ontario.

Degree-day accumulation influences annual variability in growth of age-0 walleye

The growth of age-0 fishes influences survival, especially in temperate regions where size-dependent over-winter mortality can be substantial. Additional benefits of earlier maturation and greater fecundity may exist for faster growing individuals. This study correlated prey densities, growing-degree days, water-surface elevation, turbidity, and chlorophyll a with age-0 walleye Sander vitreus growth in a south-central Nebraska irrigation reservoir. Growth of age-0 walleye was variable between 2003 and 2011, with mean lengths ranging from 128 to 231mm by fall (September 30th–October 15th). A set of a priori candidate models were used to assess the relative support of explanatory variables using Akaike's information criterion (AIC). A temperature model using the growing degree-days metric was the best supported model, describing 65% of the variability in annual mean lengths of age-0 walleye. The second and third best supported models included the variables chlorophyll a (r2=0.49) and larval freshwater drum density (r2=0.45), respectively. There have been mixed results concerning the importance of temperature effects on growth of age-0 walleye. This study supports the hypothesis that temperature is the most important predictor of age-0 walleye growth near the southwestern limits of its natural range.

Polychlorinated biphenyls in adult black bass and yellow perch were not associated with their reproductive success in the upper Hudson River, New York, USA

Although production and use of polychlorinated biphenyls (PCBs) ceased nearly 35 yr ago, questions still remain concerning the potential chronic effects these compounds may have on wild fish, including their reproductive success. In the upper Hudson River, New York, USA, fish were exposed to PCBs primarily from 2 manufacturing plants located approximately 320 km upstream of New York City, New York, from the 1940s to 1977. The authors collected yellow perch (Perca flavescens), smallmouth bass (Micropterus dolomieu), and largemouth bass (M. salmoides) using electrofishing, measured PCBs in these adults, and estimated abundance and size of their offspring at age 1 yr (age-1 fish). Fish were collected annually from 2004 to 2009 from 1 control site upstream of the PCB discharge sites and from 2 sites downstream from where PCBs were released. These sites (pools) are separated by a series of dams, locks, and canals. Muscle tissue wet weight PCB and lipid-based PCB concentrations in adults in the 2 PCB exposure pools averaged approximately 1 to 3 µg/g and 100 to 500 µg/g, respectively. Age-1 abundances were not related to adult PCB concentrations but were inversely related to river flow. Size of age-1 fish was slightly greater at the PCB-exposure sites. Levels of PCBs in yellow perch, largemouth bass, and smallmouth bass in the upper Hudson River did not impair or reduce recruitment or reproductive success.

A comparison of temporal patterns in the ocean spatial distribution of California's Central Valley Chinook salmon runs

We developed a broadly applicable method for estimating stock-specific spatial distributions based on patterns in contacts per unit effort determined from data collected in ocean fisheries. The method fully accounts for fishing effort and quantifies uncertainty in total contacts due to sampling error and the effects of annual variability in size-at-age on estimated contacts with sublegal-sized fish. As a case study, we used coded-wire tag recoveries to compare ocean spatial distributions among fish from four return run timings (fall, late-fall, winter, and spring) of Chinook salmon from the Central Valley, California, USA, and explored how distributions varied annually, seasonally, and with fish age in the data-rich fall run. All runs were rarely contacted in ocean fisheries north of Cape Falcon, Oregon (45°46′N). Late-fall and winter run fish appeared relatively restricted to the south compared with fall run fish, corresponding to life history differences and highlighting the ability of spatial management to control impacts on the endangered winter run. For the fall run, the location of highest relative contacts per unit effort of age-3 fish varied across years. This variation correlated with sea surface temperature the previous summer, suggesting ocean distributions may be more responsive to the environment than previously appreciated.

Severe glomerular disease in juvenile grey snapper Lutjanus griseus L. in the Gulf of Mexico caused by the myxozoan Sphaerospora motemarini n. sp.

In the eastern Gulf of Mexico, off the coast of Florida, grey snapper, Lutjanus griseus was found to be infected with the myxozoan parasite Sphaerospora motemarini n. sp., with high prevalence (83%) and intensity of infection occuring in age-0 fish, and with parasite levels decreasing with age (age-1 snapper 40%; age-2 snapper 0%). The morphological, molecular and phylogenetic characterisation of the myxozoan showed that it is a member of the typically marine, polysporoplasmid Sphaerospora spp. which form a subclade within the Sphaerospora sensu stricto clade of myxozoans, which is characterised by large expansion segments in their SSU rDNA sequences. Presporogonic stages of S. motemarini n. sp. were detected in the blood, using PCR. Pseudoplasmodia and spores were found to develop in the renal corpuscles of the host, causing their massive expansion. Macroscopic and histopathological changes were observed in age-0 fish and show that S. motemarini n. sp. causes severe glomerulonephritis in L. griseus leading to a compromised host condition, which makes it more susceptible to stress (catch-and-release, predators, water quality) and can result in mortalities. These results are discussed in relation to the exploitation of grey snapper populations by commercial and recreational fisheries and with the observed increased mortalities with temperature along the coast of Florida. In the future, we would like to determine prevalence and intensity of infection with S. motemarini n. sp. in juvenile L. griseus in different areas of the Gulf of Mexico in order to be able to estimate the temperature dependence of S. motemarini n. sp. proliferation and to be able to predict its distribution and severity during climatic changes in the Gulf.

Diet of Juvenile Alabama Shad (Alosa alabamae) in Two Northern Gulf of Mexico Drainages

Understanding food-web ecology is valuable to conservation by linking interactions of multiple species together and illustrating the functionality of trophic exchange. Alosa alabamae (Alabama Shad), an anadromous species, reproduces in northern Gulf of Mexico drainages from February through May, and for this study, the Pascagoula and Apalachicola rivers were chosen to sample juvenile Alabama Shad. The age-0 fish mature within these rivers and have the potential to impact the food web of the systems in which maturation occurs. The focus was to determine if diet changes as Alabama Shad mature, and to identify diet differences between drainages. Diets of Alabama Shad 50 mm SL, fed almost exclusively on insects. Many groups of aquatic and terrestrial insects were found in the stomachs of this species. Alabama Shad diets also differed among drainages, with the Apalachicola River being dominated by terrestrial insects, and the Pascagoula River having both terrestrial and aquatic insects. Diet and trophic placement of Alabama Shad may allow managers to understand the importance of this fish within its natal rivers.

Population Attributes of Lake Trout in Tennessee Reservoirs

Abstract We sampled stocked Salvelinus namaycush (Lake Trout) in Watauga Lake and South Holston Lake, TN using experimental gill nets in 2009–2010 to describe their growth, longevity, and condition. Annuli in sagittal otoliths formed once a year in early spring in both reservoirs. South Holston Lake (n = 99 Lake Trout) has been stocked since 2006, and the oldest fish was age 4. Watauga Lake has been stocked since the mid-1980s, and we collected 158 Lake Trout up to age 20. Annual mortality for age-3 and older fish in Watauga Lake was 24%. When compared to Lake Trout in northern lakes, Tennessee Lake Trout exhibited average to above-average growth and longevity. Condition of Lake Trout in both reservoirs varied seasonally and tended to be lowest in fall, but rebounded in winter and spring. Lake Trout in both reservoirs appeared to be spatially segregated from pelagic prey fishes during summer stratification, but growth rates and body condition were high enough to suggest that neither system was being overs...

The effects of cool and variable temperatures on the hatch date, growth and overwinter mortality of a warmwater fish in small coastal embayments of Lake Ontario

Little is known about the ecology of warmwater fish in small coastal embayments (<32ha) where temperatures are lowered by exchange with the adjacent lake. Using pumpkinseed (Lepomis gibbous) as a model warmwater fish, we compare hatch dates and overwinter survival in two embayments with higher and lower amounts of cold-water input from Lake Ontario, in a warmer and cooler year. In 2007, the embayments differed by approximately 2–5°C until late-July. In that year, temperatures in the cooler embayment delayed hatching times until July 18–August 20, approximately eight weeks later (May 24–August 20) than in the warmer embayment. Almost all offspring in the cooler embayment were likely too small to survive the winter. In 2008 both embayments had similar temperatures. In that year, pumpkinseed started hatching in early-June, and most were likely large enough to survive the winter. The findings from the two intensively sampled embayments were confirmed with a 21-year fish monitoring dataset; adult pumpkinseed were captured in the littoral zone of warm embayments 6–8weeks earlier than in cooler embayments. Relative to pumpkinseed in the small inland lakes of eastern and central Ontario, spawning is delayed by at least two weeks in coastal embayments. Using water temperatures as a surrogate for growth, we calculated that only 5 of the 17 embayments for which we have temperature records were able to consistently produce successfully overwintering age-0 fish. Nevertheless, we found pumpkinseed age≥1 in embayments too cold to produce age-0 pumpkinseed, suggesting immigration from warmer embayments.

Underlying causes of habitat-associated differences in size of age-0 walleye pollock (Theragra chalcogramma) in the Gulf of Alaska

Age-0 walleye pollock (Theragra chalcogramma) caught in September in the Gulf of Alaska display habitat-associated differences in standard length (SL). Age-0 fish collected in the region around Sutwik Island and 375 km farther downstream near the Shumagin Islands most likely originate from the Shelikof Strait spawning aggregation. However, age-0 fish resulting from the same spawning aggregation differ in mean size up to 20 mm between areas by September. We examined the otoliths of the larval and age-0 stages of walleye pollock from these two areas in 2000 and 2001 to determine whether growth rate, hatch date, and/or temperature influenced fish size. Circulation models were used to determine whether transport of larvae from an upstream spawning group into the study areas could have occurred. Mean in situ temperature during sampling periods was not defined as a significant factor in altering growth rates. Overlapping hatch date distributions of the larval and age-0 fish in the Shumagin Island area confirmed that the fish were from the Shelikof Strait spawning group. Comparison of hatch date distributions in the upstream Sutwik Island area revealed larger/older larvae from an upstream spawning group mixed with larvae from the Shelikof Strait spawning group. Our results suggest that the offset of 20 mm SL between the groups of age-0 pollock was the result of a combination of enhanced survivorship of early-hatched larvae in the Sutwik area and the introduction and retention of the progeny of another spawning group originating upstream of Shelikof Strait.

Identifying river of origin for age-0 Scaphirhynchus sturgeons in the Missouri and Mississippi rivers using fin ray microchemistry

Understanding linkages between natal and nursery habitats is critical for conservation of riverine fishes. Scaphirhynchus sturgeons inhabiting the middle Mississippi River may originate from the Missouri or Mississippi rivers, although relative importance of these recruitment sources is unknown. We characterized the relationship between water and sturgeon fin ray Sr:Ca, verified shifts in water Sr:Ca are recorded in age-0 sturgeon fin rays, and determined whether age-0 sturgeons from the Mississippi and Missouri rivers exhibited distinct fin ray Sr:Ca signatures. Fin ray Sr:Ca of laboratory-reared fish reflected transfer from water with elevated Sr:Ca to ambient water 1 day posthatch, indicating that short-term residency in environments can be detected. Nine of 30 age-0 fish captured in the middle Mississippi River were Missouri River emigrants. Four of these emigrants originated in the upper portion of the lower Missouri River (≥589 km upstream from its mouth), where water Sr:Ca is higher compared with the lowermost section of the Missouri River and the Mississippi River. Twenty-five of 30 fish collected from the lowermost section of the Missouri River originated within this river segment; the remainder originated upriver. Fin ray Sr:Ca enables identification of natal river segment for age-0 sturgeons and contributions of river segments to sturgeon recruitment.

Comparison of the growth of age-1 Pacific saury Cololabis saira in the Western and the Central North Pacific

The growth of age-1 Pacific saury Cololabis saira was compared based on an analysis of the body-length frequency distributions, radius of the annual ring (otolith hyaline zones; ROH), and growth patterns in otolith increments. Fish were sampled at various locations between off the Japanese coast (144°E) and in the Central Pacific (160°W) in June and July 2006, and the measurements were compared among the stations ranging over six longitudinal areas, each with a longitudinal area of 10°. The mode of body-length frequency distributions of age-1 fish was larger in fish sampled west of 160°E (size class modes of 32.0–32.5 and 31.5–32.0 cm, respectively, in each 10° longitude area) than in those sampled east of 170°E (28.5–29.0 or 29.0–29.5 cm in 3 areas). The ROH was also larger in the former group (west of 160°E) than in the latter group (east of 170°E), but hatch periods of these two groups and age in days when the hyaline zones form in August or September did not differ based on the analysis of otolith growth increments. The growth difference occurred in the period between when the fish started their northward migration and when the hyaline zone was formed. These results indicate that the habitats of the two groups were separate until at least June or July of their second year of life.

Age, Growth, and Reproduction of the Eastern Mudminnow (Umbra pygmaea) at the Great Swamp National Wildlife Refuge, New Jersey

Abstract Umbra pygmaea DeKay (Eastern Mudminnow) is one of four species of Umbridae in North America. There is little published life-history information on the species within its native range, particularly on age, growth, and reproduction. This study focuses on these aspects of the life history of this fish at the Great Swamp National Wildlife Refuge in Morris County, NJ. A total of 336 fish of seven species was collected from June 1978 through May 1979, with the Eastern Mudminnow comprising 74% of the total. The average annual growth increment in total length for the Eastern Mudminnow was 15.3 ∓ 2.06 mm, with age-1 fish averaging 40 mm total length and age-5 fish, the oldest collected, averaging 107 mm total length. The length-weight relationship was log10W = -5.291 + 3.182 log10TL mm for males and log10W = -4.999 + 3.032 log10TL mm for females. We observed no statistically significant sexually dimorphic differences in length-weight relationships in this population. The ratio of females to males increase...

Comparing the nursery role of inner continental shelf and estuarine habitats for temperate marine fishes

Abstract The marine-estuarine transition represents an important biogeographic boundary, yet juvenile marine finfish have been observed in both temperate inner continental shelf (ICS) and estuarine habitats during the summer nursery period. In a direct comparison of ICS and estuary nurseries, spatial and temporal patterns in species composition, biodiversity, size structure, and relative abundance of age-0 fishes were tested using contemporaneous data from multiyear (2004–2006) trawl surveys of the Maryland ICS near Assateague Island, MD, and lower Chesapeake Bay, VA (estuary). Survey data from both habitats showed similar seasonal progression of assemblage structure, biodiversity phenologies, and dominant species identities. Late summer densities for four of five numerically dominant species varied by habitat. Densities of bay anchovy Anchoa mitchilli , weakfish Cynoscion regalis , and Atlantic butterfish Peprilus triacanthus were higher in the ICS; whereas summer flounder Paralichthys dentatus density was higher in the estuary. Density of spot Leiostomus xanthurus did not differ between habitats. Apparent daily growth rates of these five species, as estimated by modal length progression, were not significantly different between the two habitats. Although individual species displayed varying affinities for ICS versus estuarine habitats, this study provides strong evidence that the ICS of the Middle Atlantic Bight is capable of functioning interchangeably with polyhaline estuarine regions as nursery habitat for a diverse group of marine finfish.

The combined effect of bottom-up and top-down factors on life history and reproduction of Daphnia in the field: is a strategic dilemma underlying population declines?

In a detailed field study covering three years, population dynamics, life history shifts and reproductive patterns of a population of Daphnia galeata were investigated in relation to food availability and dynamics of young of the year fish, the main vertebrate predators. In all years an increase of Daphnia abundance in spring was associated with declining food conditions (clear water stage). The size at maturity (SAM) during this period was high and even increased, brood size declined, while egg volume increased. These patterns may be explained as response to food limitation. A decline of Daphnia abundance in every year was associated with increasing food conditions and the end of the clear water stage. Egg volumes as well as the size of egg-carrying daphnids also decreased, while brood size remained at low values. In two years in which these changes were particularly pronounced, the available fish data suggest that both the biomass (determining predation pressure), as well as the size of the fish (determining size selection) are important for the observed dynamics. No decrease of SAM occurred as long as fish were smaller than 25 mm TL, when they are still gape-limited and not able to feed on the largest size-classes of Daphnia. Although fish biomass, which should correspond to kairomone level, would have suggested a reduction of SAM as induced defence, probably the selection of small (egg-carrying) daphnids by small fish, besides severe food limitation, prevented this response to become effective. The sudden decline of SAM at the end of the clear water stage may not be explained by gradual phenotypic responses or indirect demographic effects, but must be due to an alternation of generations. SAM may be further reduced by direct and indirect effects of predation, interacting with increasing food levels. The Daphnia population is most vulnerable to predation at the time when the new generation takes over. Consequently, predation impact depends on timing of both age-0 fish consumption and feeding selectivity.

White bass population demographics in a northwestern South Dakota reservoir

The white bass (Morone chrysops) is an important sport fish species in the upper Midwest. As such, understanding white bass dynamics is critical for managing its populations. Thus, we evaluated population dynamics of white bass in a northwestern South Dakota reservoir and attempted to determine whether bass recruitment patterns were more related to reservoir inflows or spring weather patterns. We found that white bass growth increased from 243 mm for age-2 fish, to 322 mm for age-6 fish, and then to 346 mm at age 9. The total annual mortality rate was 29.7%. In terms of year-class strength, white bass recruitment was erratic. The recruitment pattern was more related to spring weather patterns than reservoir inflow. In comparison, white bass population dynamics in this South Dakota irrigation reservoir were more similar to those of white bass populations in Midwestern glacial lakes than those found in southern US reservoirs.