Young-of-year Research Articles

Interspecific variation in migratory fish recruitment in the Upper Paraná River: effects of the duration and timing of floods

This study evaluated the relationship between the young of year (YOY) abundance of migratory fish species and the interannual variations in the duration and delay of floods in the Upper Parana River floodplain. YOY of the most abundant migratory species Brycon orbignyanus, Hemisorubim platyrhynchos, Leporinus elongatus, Leporinus macrocephalus, Leporinus obtusidens, Pseudoplatystoma corruscans, Pterodoras granulosus, Prochilodus lineatus, Salminus brasiliensis and Sorubim lima were studied in a stretch of the Parana river influenced by dams. Multiple regression analyses were performed with flood duration and delay as predictors for YOY abundances. There were differences among the species in the responses to flood duration and delay. The species B. orbignyanus, L. elongatus, L. macrocephalus, L. obtusidens, and P. lineatus exhibited an exponential increase in YOY abundance with flood duration. An exponential decrease in YOY abundance with flood delay was found for most of the studied species. Nevertheless, flood delay and flood duration were significant predictors of YOY abundance for L. elongatus, L. obtusidens, P. corruscans and P. lineatus. For these species, flood delays may result in failure of recruitment because these species migrate early in the season to adjust their energy reserves and their swimming patterns. Therefore, any efforts to preserve migratory fish should consider discharge manipulation from reservoirs upstream of the study areas. It is crucial that reservoirs are operated in such a way that the quantity, duration and timing of water release are compatible with the viability of spawning and the survival of early life stages of migratory fish.

Genetic monitoring of trout movement after culvert remediation: family matters

We contrasted various genetic analyses to evaluate their utility and constraints for detecting movement of cutthroat trout (Oncorhynchus clarkii) through restored culverts in different field settings: population-level metrics of genetic variability (heterozygosity and allelic richness); Bayesian clustering and assignment of individual genotypes from age 1+ fish; and a novel “sib-split” approach, where movement patterns are extracted from the spatial distribution of young-of-year (YOY) full-sibling groups inferred via pedigree reconstruction. Family structure greatly influenced population-level and individual clustering results in our small headwater populations, even though field sampling was implemented to avoid siblings. Sib-split, which uses family structure to detect movement, uncovered passage of YOY just weeks after emergence. When retrospectively applied to older individuals, it proved essential in interpreting clustering patterns and captured passage in several families of 1- and 2-year-olds. Where family structuring may negatively affect genetic analyses or, alternatively, be prominent enough to allow application of sib-split is difficult to predict a priori; we discuss benefits and limitations of all approaches under different ecological, spatial, and management scenarios.

Population ecology and seasonal demography of the endangered grotto sculpin (Cottus specus)

AbstractSubterranean fishes are understudied worldwide and often at risk before their populations are discovered and described. The nature of karst systems limits the applicability of ecological paradigms and hinders our ability to identify and preserve endemic fauna. Aquatic karst taxa in particular are subject to environmental threats that increase in severity over time. Once a population or species is recognised as distinct, it is imperative we gain understanding of its biology to inform effective resource management and mitigate risk factors. The grotto sculpin (Cottus specus) is endemic to Perry County, Missouri, U.S. caves and was formally described and listed as endangered under the U.S. Endangered Species Act in 2013. We used mark–recapture methods to quantify population densities and estimate population sizes in two caves and two corresponding spring branches. Size structure varied among habitats and seasons. Spring branches were dominated by juveniles year‐round with peak young‐of‐year (YOY) densities in May. Adult densities in both macrohabitats decreased in winter, possibly due to recruitment or seasonal stress, and were lower at spring branches compared to caves and declined further during late winter which may be indicative of cave spawning. YOY were captured variably underground with peak densities in summer. The ecology of grotto sculpin appears to be more complex than has been reported previously for subterranean fishes. Variable patterns of demography requiring multiple contiguous habitats are unique for cave species and support the recently substantiated suggestion that subterranean systems are not as simple or disconnected as once thought.

Univariate functions versus fuzzy logic: Implications for fish habitat modeling

Univariate functions, like the Habitat Suitability Criteria (HSC) for each species life-stage, consider separate effects of individual parameters. Other than using independent univariate functions, knowledge-based models as the fuzzy logic approach are based in the establishment of fuzzy sets and rules for each species life-stage built on a fish biologists’ expert judgment. Nonetheless, results from HSC and fuzzy logic may differ significantly and, thus increase the difficulty to choose between these two approaches. With the aim to compare and assess differences from using HSC and fuzzy logic methodologies, the habitat requirements for the Southwestern arched-mouth nase (Iberochondrostoma almacai), partitioned by life-stages, were set based on data collection and on expert judgment. The Weighted Usable Area (WUA) and Hydraulic Habitat Suitability (HHS) were calculated by means of a two dimensional model using the HSC and considering three different mathematical combinations of the independent parameters (i.e. product, arithmetic mean and geometric mean) and using the fuzzy logic approach. Simulations yielded different results, especially for the young-of-year (YOY), therefore affecting the final profile habitat versus discharge curves. Knowledge on species requirements proved to be scarce, thus, preventing the attainment of conclusive results. The product combination of the HSC returned the lowest habitat values, whereas the arithmetic mean stepped closer to the fuzzy logic habitat results. Discharge thresholds obtained were substantially different among the different mathematical combinations of HSC and fuzzy logic. Habitat outputs translated in HHS exhibited a clear maximum value of habitat for a specific discharge, whereas the WUA versus discharge curves performed an asymptotical trend disabling the selection of a discharge threshold. Results from this study suggest the use of HHS as the habitat output and the use of HSC when expert knowledge over a species is scarce.

Isolated salt marsh colonization by a resident species, mummichog (Fundulus heteroclitus), and a transient species, pinfish (Lagodon rhomboides)

The potential for species to populate habitat patches is directly influenced by dispersal and colonization abilities. To test the dispersal and colonization capabilities of a resident, mummichog (Fundulus heteroclitus), and a transient, pinfish (Lagodon rhomboides), marsh species, isolated-island marsh sites were used for removal and colonization assessments, while a nearby non-removal site was used to concurrently monitor temporal catch variability. F. heteroclitus and L. rhomboides were removed from island marshes using baited minnow traps during mid-fall 2004 (after F. heteroclitus spring/summer spawn, and prior to L. rhomboides winter recruitment), then monitored for colonization through the peak F. heteroclitus spawning season the following year (July 2005). Significant abundance reductions occurred for F. heteroclitus and L. rhomboides due to removal efforts, and for L. rhomboides due to temperature-dependent offshore migration. F. heteroclitus and L. rhomboides were capable of seasonally colonizing marsh sites separated by >800m of open water, which was twice the previously documented distance for F. heteroclitus movement within marsh habitats. Results from size-class analysis indicated that F. heteroclitus populated sites via adult colonization from nearby marshes within weeks to months of removal. L. rhomboides site colonization occurred by young-of-year (YOY) recruitment and was documented within months of removal efforts, when YOY attained sufficient size for gear collection. Low population contribution by F. heteroclitus YOY to island compared to mainland type marsh indicated that island marshes were primarily sustained by immigrants, which colonized during late fall and winter, while YOY production sustained the population at the mainland marsh. Island marshes acted as sinks for estuarine F. heteroclitus populations. F. heteroclitus population characteristics were determined during: (1) the spring/summer spawn and recruitment, and (2) the late fall/winter dispersal–colonization by adult F. heteroclitus. Further, the F. heteroclitus dispersal–colonization phase maintains the species' large-scale (geographic) distribution, while the spawn–recruitment phase maintains the small-scale (local) populations. L. rhomboides recruitment and dispersal–colonization occur simultaneously during late fall/winter when pulsed dispersal–colonization by recruits maintains geographic and local populations.

Spatial linkages between settling young-of-year and older juvenile lobsters

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 499:143-155 (2014) - DOI: https://doi.org/10.3354/meps10625 Spatial linkages between settling young-of-year and older juvenile lobsters Victoria H. M. Burdett-Coutts1,*, Richard A. Wahle2, Paul V. R. Snelgrove1, Rémy Rochette3 1Biology Department and Ocean Sciences Centre, Memorial University of Newfoundland, St. John’s, Newfoundland A1C 5S7, Canada 2School of Marine Sciences, University of Maine, Darling Marine Center, Walpole, Maine 04573, USA 3Biology Department, University of New Brunswick, Saint John, New Brunswick E2L 4L5, Canada *Corresponding author: vbcoutts@gmail.com ABSTRACT: We examined spatial association between young-of-year (YoY) and older juvenile (Juv) American lobsters Homarus americanus across multiple spatial scales using 8 years (2001 to 2008) of field measurements of a long-term settlement index time series from New England, USA. Complementary laboratory experiments examined behavioural responses of settling postlarvae to conspecific presence. Regional scale (10s to 100s of kilometres) data aggregation showed significant association between YoY recruitment and Juv densities in the same year for all 8 years examined. These broad-scale positive associations support previous research showing the importance of circulation-driven patterns of larval supply in linking newly settled YoY and Juv lobsters. Analysis at the quadrat scale, however, showed greater than expected association between YoY and Juv, suggesting a behavioural component. Early benthic-phase Juv lobsters (~0 to 2 yr old) strongly associate with structurally complex habitats; however, little is known of other habitat quality variables that may enhance successful recruitment. Resident conspecifics may represent one of several habitat quality proxies for postlarval lobsters despite post-settlement risk in settling among conspecifics, such as competition and predation. In short-term (4 min) laboratory behavioural experiments, postlarvae spent significantly more time on the bottom in the presence of conspecific juveniles. In longer-term (24 h) experiments, postlarvae initially (<1 h), though not significantly, settled more rapidly in the presence of conspecific juveniles, and any weak effect dissipated with time. Lack of suitable habitat in experimental chambers may have inhibited a longer-term response. While conspecifics may initially attract postlarvae, settlement may require additional habitat cues. KEY WORDS: Lobster · Postlarvae · Bottom-searching behaviour · Conspecific cues · Behaviour · Scaling · Recruitment Full text in pdf format PreviousNextCite this article as: Burdett-Coutts VHM, Wahle RA, Snelgrove PVR, Rochette R (2014) Spatial linkages between settling young-of-year and older juvenile lobsters. Mar Ecol Prog Ser 499:143-155. https://doi.org/10.3354/meps10625 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 499. Online publication date: March 03, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Exploitation by Common Carp (Cyprinus Carpio) of A Floodplain Wetland of The Lower River Murray Under Drought and Flooding Conditions

Common carp Cyprinus carpio are a declared pest fish throughout the Murray-Darling Basin. Successful management of this highly-invasive species aimed at mitigating its detrimental effects on aquatic ecosystems is therefore a priority issue for wetland restoration and rehabilitation programmes for the benefit of native fish communities. as part of a large-scale, field-based experiment on carp impacts, a population of carp was extensively sampled from 2009 to 2011 at Brenda Park wetland (lower River Murray, South Australia) under both drought and flooding conditions. a consistent young-of-year (YoY) cohort was present in the 2009–10 breeding season, indicating successful spawning within the wetland. However, the same cohort appeared not to leave the wetland later in the season, possibly as a result of drought-induced low-flow conditions. Conversely, there was no evidence for within-wetland spawning in 2010–11 and 2011–12. Following a major flood event in Summer/autumn 2011, a consistent stock-size (210–440 mm TL) component was present in the carp population. Despite one successful spawning event out of the three breeding seasons of sampling, it cannot be ruled out that Brenda Park can act as a recruitment hot-spot for carp, especially in light of the large-scale population dynamics of this species. Measures for wetland rehabilitation should account for this and rely on a combination of flow regulation practices, enhancement of native fish passage and integrated carp management/control measures involving use of selective traps or exclusion screens, removal programmes and, whenever feasible, water draw-downs.

Influence of Salt Marsh Size and Landscape Setting on Salt Marsh Nekton Populations

Recruitment- and predation-related effects on populations of salt marsh codominants mummichog (Fundulus heteroclitus) and pinfish (Lagodon rhomboides), were examined based on marsh size and landscape setting. Six island marshes—three small island marshes (SIM) ~40–1,000 m2 and three large island marshes (LIM) ~3,000–10,000 m2—were paired with six expansive fringing marshes (EFM), each >76,000 m2 in size and located within ~1.0 km of a paired SIM or LIM. Over a 2-year period, triannual collections at these sites assessed F. heteroclitus, L. rhomboides, and predator finfish populations as well as habitat characteristics. No significant population density trends were apparent for L. rhomboides young-of-year (YOY) or year-one-and-older (Y1+) cohorts based on marsh size or were any significant differences in density apparent among marsh types. F. heteroclitus YOY and Y1+ densities differed significantly among marsh types demonstrating a positive relationship between density and marsh size. Larval and juvenile F. heteroclitus abundances were significantly lower within SIM than LIM and EFM. Although larval F. heteroclitus abundances between LIM and EFM did not differ significantly, juvenile abundances did, suggesting mortality constrained LIM juvenile abundances. A significant negative relationship of F. heteroclitus to predator finfish density and a significant negative relationship of predator finfish density to low marsh area/perimeter (access restriction) estimates suggest that predation on F. heteroclitus is greater within SIM and LIM than within EFM. Habitat and landscape level attributes can affect resident nekton population regulation and these effects should be considered relative to the life history traits of targeted species when managing coastal resources.

Riverine flow and spawning requirements of Macquaria ambigua oriens: implications for conservation and management

Understanding the life-history attributes of aquatic species is integral to the development of environmental-flow strategies in regulated river systems. This is particularly important when species are under continual and increasing pressure from water-resource development. In this study, the water temperature and flow requirements for spawning of the Fitzroy River golden perch (Macquaria ambigua oriens) were investigated over 4 years at 22 sites in the Fitzroy River catchment. Eggs, larvae and young-of-year (YOY) M. ambigua oriens were sampled on a variety of flow events to determine the environmental requirements for spawning. Eggs and larvae of M. ambigua oriens were detected during natural flow events generally with a minimum of 1.5 m river rise and duration of 7 days. Spawning was associated with the peak and/or recession of the first or second post-winter flow event where water temperatures exceeded 24°C. Our data suggests that it is important to protect a range of flows, not just flood flows, as previously documented for this species. The interaction of spawning flows with existing and future water-resource development should be considered to ensure maintenance of the population viability of M. ambigua oriens.

Fluctuations in food supply drive recruitment variation in a marine fish

Reproductive rates and survival of young in animal populations figure centrally in generating management and conservation strategies. Model systems suggest that food supply can drive these often highly variable properties, yet for many wild species, quantifying such effects and assessing their implications have been challenging. We used spatially explicit time series of a well-studied marine reef fish (black surfperch Embiotoca jacksoni) and its known prey resources to evaluate the extent to which fluctuations in food supply influenced production of young by adults and survival of young to subadulthood. Our analyses reveal: (i) variable food available to both adults and to their offspring directly produced an order of magnitude variation in the number of young-of-year (YOY) produced per adult and (ii) food available to YOY produced a similar magnitude of variation in their subsequent survival. We also show that such large natural variation in vital rates can significantly alter decision thresholds (biological reference points) important for precautionary management. These findings reveal how knowledge of food resources can improve understanding of population dynamics and reduce risk of overharvest by more accurately identifying periods of low recruitment.

Environmental correlates of signal crayfish, Pacifastacus leniusculus (Dana, 1852), density and size at two spatial scales in its native range

ABSTRACT While much literature exists on the ecology and ecosystem impacts of signal crayfish, Pacifastacus leniusculus (Dana, 1852), as an invasive species, little information exists on the ecology of this species in its native range in the Pacific Northwest, USA. Signal crayfish (P. leniusculus leniusculus) were collected from the Umatilla River in northeastern Oregon, USA, where they are native. Collecting occurred during the summer at 13 sites spanning the longitudinal gradient of the river to examine the relationship between density and size of individuals and environmental factors at two spatial scales. At the reach scale (100+ m2) the density of young-of-year (YOY), and age 1+ female and male crayfish was positively associated with substrate size. Additionally, age 1+ female and male crayfish density was negatively associated with the amount of crop agriculture. Substrate size was also important in determining the density and size of crayfish at the microhabitat scale (<1 m2) with greater densities...

Selected Habitats of Slimy Sculpin in Coldwater Tributaries of the Upper Mississippi River in Minnesota

Slimy sculpin Cottus cognatus are being reintroduced into coldwater streams in the upper Midwestern United States, where they were extirpated by stream degradation during the early- to mid-1900s. Habitat use and selection by slimy sculpin were examined in nine coldwater tributaries of the Upper Mississippi River in southeastern Minnesota to determine which stream habitats are important for successful reintroduction. Most (>70%) individuals (n = 1932) used coarse substrates and vegetation, shallow water (<30 cm), slow current velocities (<20 cm/sec), and moderately embedded (15–60%) substrates. Compared to habitat availability, adults selected boulder substrate and vegetation, whereas young-of-year (YOY) selected gravel, rubble, and vegetation. YOY sculpin selected shallow water (<30 cm), whereas adults exhibited broader selection (1–60 cm). Both age groups selected the slower bottom velocities (especially <20 cm/sec). Habitat use and selection by adult fish were consistent among 3 y of surveys. Habitat suitability index values for sculpin were similar among native sculpin streams and streams where sculpin have been or may be reintroduced within the same geographic region. Slimy sculpin displayed habitat selection similar to that of other sculpin species, except for selecting much slower current velocities. Suitable physical habitats are present in coldwater streams in southeastern Minnesota to support further reintroduction of slimy sculpin. Failed reintroductions of sculpin likely are not related to lack of suitable physical habitats.

Effect of winter feeding and starvation on the growth performance of young-of-year (YOY) great sturgeon,Huso huso

Summary The objective of this study was to evaluate the feeding rate of the great sturgeon (Huso huso) young of the year (YOY) and to investigate the effects of different feeding rates in maintaining the weight of fish during short periods of winter starvation. Six feeding rates of 0.2, 0.4, 0.6, 0.8, 1.0% body weight (BW) day−1 and feeding to satiation were considered for the first experiment. Each feeding rate was randomly assigned to three replicate tanks, with continuous feeding throughout a 5-week winter period of water temperatures below 10°C. Fifteen fish were held in each of 18 tanks with an average initial body weight of 219.6 ± 6.9 g. After 5 weeks of feeding, the best performance was observed in fish fed 1% BW day−1, but negative growth was observed in fish fed 0.2% BW day−1. In the second experiment, fish were deprived of feed for 3 weeks at winter temperatures. Weights and condition factors of all fish decreased during starvation, while the differences in mean weight before and after the starvation period were not significant in fish fed a level of 0.2% BW day−1 and those fish fed to satiation. No mortality was recorded in either experiment. Results of this study indicate that a feeding rate of 1% BW day−1 would be sufficient for commercial fish farming of YOY of this species to maintain them over winter. Also, to maintain fish weights and prevent weight loss in overwintering ponds, a feeding rate of around 0.3% BW day−1 seems appropriate for hatcheries.

Variation in native micro-predator abundance explains recruitment of a mobile invasive fish, the common carp, in a naturally unstable environment

Why certain species of fish become invasive is poorly understood and a key obstacle to restoring many of the world’s ecosystems. In this study we tested whether variation in biotic resistance exerted by native predators might explain the reproductive success of the common carp, a large and fecund invasive species that typically spawns in outlying and unstable shallow habitat. An initial three-year study of the relative abundance of young-of-year (YOY) carp in interconnected lakes in the Upper Mississippi River Basin discovered that YOY carp are only found in shallow waters that experience winter hypoxia (winterkill) and have low densities of the native egg-predators that otherwise dominate these locales. A follow-up experiment tested if native fish predation on carp eggs could explain this distribution. It found that while carp eggs survived in winterkill lakes, they only survived in non-winterkill lakes when protected by a mesh that excluded fish. Large numbers of carp eggs were found in the stomachs of native fish inhabiting lakes that did not winterkill. We conclude that common carp, and likely many other highly mobile and fecund invasive fish, have evolved life histories to avoid egg predators and can become invasive when they are absent.

Seasonal and ontogenic migrations of meagre (Argyrosomus regius) determined by otolith geochemical signatures

Argyrosomus regius uses different water masses during its life history, being associated with estuaries for reproduction. In order to study the life history and migration patterns, variations in otolith Na, Sr and Ba were measured by laser ablation-ICPMS along transects running from the first year of life to the otolith edge, comprising up to 12 years of age. Visual and statistical modelling approaches were used to analyse both individual- and population-level patterns. Ontogenetic trends in Sr:Ca and Ba:Ca followed a sigmoidal increase over the life span, with an inflection point in Sr:Ca occurring at 5 years of age in males and 6.6 in females, suggesting respective age at maturity. Using reared young-of-year (YOY) meagre for validation, the habitat use of wild fish was characterized and our data suggest that most fish spend the first 2–4 years in offshore waters, and begin moving between water masses after age 6. Population-level analyses indicated significant seasonal variations, with a larger proportion of fish with high otolith Sr:Ca in the spring and summer. Although Sr:Ca would normally be expected to be lower after movement into estuaries, in this case the increase could mark gonad maturation and spawning activity. Alternatively, since the Sr:Ca maxima correspond to higher otolith Ba:Ca in the summer, fish would have moved into the estuarine area, especially since the Guadalquivir river drains metal-rich areas with heavy mining activities leading to elevated Sr concentrations compared to adjacent coastal waters.

Complex littoral habitat influences the response of native minnows to stocked trout: evidence from whole-lake comparisons and experimental predator enclosures

Strong negative effects of introduced predatory fishes on native species are frequently reported but may not be universal. Recent research from productive lakes, for example, has documented few serious negative effects. Our objective was to determine how complex littoral habitat mediates the response of adult and young-of-year (YOY) native dace (Chrosomus spp.) and fathead minnow (Pimephales promelas) to the introduction of rainbow trout (Oncorhynchus mykiss) in productive lakes in Alberta, Canada. We first quantified inshore–offshore habitat use of native fish in stocked and unstocked lakes with heavily vegetated littoral zones. We then manipulated the presence or absence of trout and densities of macrophytes within enclosures in an unstocked lake and assessed the behavioral response of native fish. Our whole-lake comparisons revealed that adult and YOY fishes occurred in vegetated inshore areas to a greater extent in stocked relative to unstocked lakes. In the enclosure experiment, native fishes did not respond to the introduction of trout at natural macrophyte densities, but dace significantly reduced their occupation of enclosures with reduced macrophytes once trout were added. Our results suggest that complex littoral macrophyte beds provide important refuge habitat for native fishes, which can potentially mitigate negative effects associated with introductions of a piscivorous predator.

Stocked trout do not significantly affect wood frog populations in boreal foothills lakes

Stocking salmonids into lakes can have negative consequences for some ecosystem components, including amphibians. In the boreal foothills of Alberta, Canada, we compared populations of wood frog ( Lithobates sylvaticus ) at lakes with (n = 5) and without (n = 6) stocked trout over 3 years; all 11 lakes also supported native populations of forage fishes. Abundance and size of adult and young-of-year (YOY) frogs did not differ significantly between stocked and unstocked lakes. We also compared the wood frog population from a twelfth, fishless lake with populations from the 11 fish-bearing lakes (with or without trout); abundance and size of adults and YOY were greater, and YOY emerged earlier in the absence of fish. Based on patterns compiled from a literature review of effects of stocked trout on anuran amphibians, we suggest that characteristics of our study systems, including the presence of native fish, the length of the anuran larval period, lake trophic status, and the existence of complex, littoral habitats, contributed to the lack of major impacts of stocked trout on wood frog populations.

Behavioral Observations of Lilliputian Piscivores: Young-of-YearSphyraena barracudaat Offshore Sub-Tropical Reefs (NW Atlantic Ocean)

Abstract Direct observations were made in June 2009 and 2010 of newly recruited young-of-year (YOY) Sphyraena barracuda (Great Barracuda; 50–80 mm total length) occuring on “live bottom” sub-tropical reefs off the southeast US at depths of 18–25 m. Counts of YOY fish from roving diver surveys along multiple reefs with under-cut ledges ranged from 0–122 individuals, indicating patchy distributions at the scale of individual reefs. Individual fish occured in groups of 2–20+, primarily along the undercut side of ledges, where dense schools of Haemulon aurolineatum (Tomtate), Decapterus punctatus (Round Scad), Decapterus macarellus (Mackeral Scad), Stenotomus chrysops (Scup), and Atherinid sp. (silverside) were concentrated. Groups of YOY Great Barracuda attacked, captured and consumed YOY Tomtate and Silverside that occured in schools in the water column adjacent to (just above the sediment-water interface) and directly above the undercut edge of the reefs. Prey reacted during attacks by reducing nearest nei...

IMPORTANCE OF TRIBUTARY STREAMS FOR RAINBOW TROUT REPRODUCTION: INSIGHTS FROM A SMALL STREAM IN GEORGIA AND A BI‐GENOMIC APPROACH

ABSTRACTTributaries of tailwater fisheries in the southeastern USA have been used for spawning by stocked rainbow trout (Oncorhynchus mykiss), but their importance may have been underestimated using traditional fish survey methods such as electrofishing and redd counts. We used a bi‐genomic approach, mitochondrial DNA sequences and nuclear microsatellite loci, to estimate the number of spawning adults in one small tributary (Cabin Creek) of the Chattahoochee River, Georgia, where rainbow trout are known to spawn and have successful recruitment. We extracted and analysed DNA from seven mature male rainbow trout and four juveniles that were captured in February 2006 in Cabin Creek and from 24 young‐of‐year (YOY) trout that were captured in April 2006. From these samples, we estimated that 24 individuals were spawning to produce the amount of genetic variation observed in the juveniles and YOY, although none of the mature males we sampled were indicated as sires. Analysis of the mitochondrial D‐loop region identified four distinct haplotypes, suggesting that individuals representing four maternal lineages contributed to the offspring. Our analyses indicated that many more adults were spawning in this system than previously estimated with direct count methods and provided insight into rainbow trout spawning behavior. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Spatial and temporal variabilities of δ13C and δ15N within lower trophic levels of a large lake: implications for estimating trophic relationships of consumers

Stable isotopes of carbon (δ13C) and nitrogen (δ15N) often have unique values among lake habitats (e.g. benthic, littoral, pelagic), providing a widely used tool for measuring the structure and energy flow in aquatic food webs. However, there has been little recognition of the spatial and temporal variabilities of these isotopes within habitats of aquatic ecosystems. To address this, δ13C and δ15N were measured in seston, zebra mussels (Dreissena polymorpha) and young-of-year (YOY) yellow (Perca flavescens), and white perch (Morone americana) collected from four sites across the offshore habitat of the western basin of Lake Erie during June–September 2009. Values of δ13C and δ15N showed significant spatial and temporal variations, with month accounting for >50% of the variation, for both stable isotopes and all the species except seston. Such variation in isotope values has the potential to significantly influence or confound interpretation of stable isotopes in measures, such as trophic position (TP) which use lower trophic level organisms as their baseline. For example, TP was found to vary up to 0.7 for yellow and white perch (TP = δ15Nfish − δ15Nzebra mussel/diet-tissue fractionation factor) depending on the zebra mussel data used (e.g., from a different location or a different collection month). As the use of stable isotopes continues to move from qualitative to more quantitative measures of trophic structure, food web research must recognize the importance of stable isotopes' variability in lower trophic level organisms, especially in large lake systems.