Habitat utilization of juvenile lake sturgeon, Acipenser fulvescens, in a large Canadian river

An increased understanding of the juvenile life history stage of the lake sturgeon, Acipenser fulvescens , has been recognized as a key requirement for improving conservation efforts for this once abundant species. The objectives of the current study were to develop an effective methodology for capturing juvenile lake sturgeon in a large riverine environment; to describe the physical habitat characteristics (depth, water velocity and substrate) associated with the areas where juvenile lake sturgeon were captured; and to determine basic population parameters (length, body mass and condition factor) for juvenile lake sturgeon captured in those areas. Gillnets (mesh sizes 25–108 mm) were used to sample the Winnipeg River, a large river in the northern extent of the species range, from 12 June to 6 November 2006. A total of 2154 juvenile (<530 mm FL) lake sturgeon were captured, which represented over 74% of the total fish catch. Moderate (51–108 mm) and small (25 mm) mesh gill nets were found to be efficient for sampling juvenile lake sturgeon, with the former capturing a wider range of sizes and the latter capturing fewer fish but resulting in decreased mortality. Juvenile lake sturgeon were captured at high densities in discrete areas characterized by water depths >13.7 m, detectable water velocities >0.20 m s⁻¹, and various substrate types.     

Existence of a macrophyte-dominated clear water state over a very wide range of nutrient concentrations in a small shallow lake

Little Mere, a small shallow lake, has been monitored for four years, since its main source of nutrients (sewage effluent) was diverted. The lake has provided strong evidence for the persistence of a clear water state over a wide range of nutrient concentrations. It had clear water at extremely high nutrient concentrations prior to effluent diversion, associated with high densities of the large body-sized grazer, Daphnia magna, associated with low fish densities and fish predation. Following sewage effluent diversion in 1991, the nutrient concentrations significantly declined, the oxygen concentrations rose, and fish predation increased. The dominance of large body-sized grazers shifted to one of relatively smaller body-sized animals but the clear water state has been maintained. This is probably due to provision of refuges for grazers by large nymphaeid stands (also found prior to diversion). There has been a continued decrease in nutrient concentrations and expansion of the total macrophyte coverage, largely by submerged plants, following effluent diversion. The grazer community of Little Mere has also responded to this latter change with a decline in daphnids and increase in densities of weed-associated grazers. The presence of large densities of such open water grazers was the apparent main buffer mechanisms of the clear water state until 1994. The lake has, so far, maintained its clear water in the absence of such grazers. Thus, new buffer mechanisms appear to operate to stabilize the ecosystem. Little Mere appears to have shifted from previous top-down controlled clear water state to a bottom-up controlled clear water state.     

FUNDUDZI,A UNIQUE,SACRED AND UNKNOWN SOUTH AFRICAN LAKE

Summary

Lake Fundudzi is a unique, small inland lake in the north eastern region of South Africa, formed by a landslide. The considerable sedimentation of its basin indicates an age in the order of 10 000s of years. It forms the focus of a rich heritage of ceremonial rituals and myths amongst the local Vhavenda population, but has not enjoyed the protection it deserves and serious impacts have been made by human transformation of the catchment, over-utilization of natural resources, forestry, water abstraction and degradation of the rivers. Additionally, the present fish community is not natural as all larger fish species seem to have been introduced. Some limnological information on this lake has been sporadically collected over a period of 60 years. It indicates conductivities ranging between 2,8 ?18,8 μ S m^?1 neutral to acid waters and oxygen stratification near the bottom during winter. Zooplankton was characterised by small copepods and rotifers. The lake is presently threatened by an increased anthropogenic sedimentation rate. It deserves national and international conservation status and can become a valuable ethno- and eco-tourist attraction provided proper management and conservation are applied. Data are insufficient for management, and a research programme focusing on hydrology and limnology should be initiated.     

Phytoplankton biomass in Lake Xolotlán (Managua): Its seasonal and horizontal distribution

Some well-documented studies on restoring eutrophic lake systems in The Netherlands by fish stock management have been evaluated with the emphasis on the role of macrophytes. Furthermore, the factors determining the light climate for submerged macrophytes in a large shallow eutrophic lake (Lake Veluwe) have been assessed and the potential success of biomanipulation in large scale projects is discussed. Today relatively little attention has been paid to macrophyte management although the importance of macrophytes in lake restoration has been recognized regularly. The biomanipulation strategy was successful in small scale projects. In a large scale project, however, wind-induced resuspension may largely determine the underwater light climate through attenuation by the water column and periphytic layer. Therefore, restoration of relatively large waterbodies by fish stock management only is expected not to lead to any noteworthy improvement of the light climate for submerged macrophytes. Additional measures aimed at reducing wind-induced resuspension of sediment particles and reestablishing of the macrophyte stands are required for successful biomanipulation strategies. Water quality managers should pay more attention to macrophyte stands in biomanipulation projects because macrophytes enhance a more stable and diverse ecosystem. Restoration objectives and the methods of their achievement must be carefully planned since an abundant submerged macrophyte vegetation may have undesirable effects as well.     

Effects of Introduced Groundwater on Water Chemistry and Fish Assemblages in Central Florida Lakes

We assessed effects of groundwater pumping to elevate lake levels on lake water chemistry and fish population metrics at seven Florida lakes. Following groundwater pumping, lake level fluctuation was reduced and lake water samples increased in mean pH, total alkalinity, total phosphorus, chloride and Secchi depth compared to historical means, indicating a close resemblance to the chemistry of aquifer water in the region. Fish community metrics from the augmented lakes were compared to 36 non-augmented lakes in Florida. The mean values for catch per unit effort, species richness and biomass of harvestable fishes, determined by electrofishing, were lower in augmented lakes compared to non-augmented lakes. Canonical correspondence analysis (CCA) indicated a high probability of a low abundance of individual species in augmented lakes compared to a majority of non-augmented lakes. The augmented lake with the lowest pumping rate exhibited less of a shift in limnological variables from historical values, and had fish population characteristics more closely resembling those of non-augmented lakes. Thus, reduced volumes of groundwater introduction could lower impacts to limnological and fish population characteristics. Augmentation allows for lakes to be utilized for recreational activities, and without augmentation some lakes in central Florida would likely go dry due to groundwater withdrawals for water supply. Therefore, allowing more natural water level fluctuations and possible reductions in total pumpage are recommended to reduce impacts to limnological and fish population characteristics, while still allowing sufficient groundwater pumping to preserve lake habitats.     

Validation of mark‐recapture population estimates for invasive common carp,Cyprinus carpio,in Lake Crescent,Tasmania

A mark‐recapture study based on the Petersen method was implemented in 1998 to estimate the abundance of the invasive common carp, Cyprinus carpio L., in Lake Crescent, Tasmania. Multiple gear types were employed to minimise capture bias, with multiple capture and recapture events providing an opportunity to compute and compare Petersen and Schnabel estimates. A single Petersen estimate on recapture data and two Schnabel estimates – one each on mark (forward‐Schnabel estimate) and recapture (reverse‐Schnabel estimate) data – were conducted. An independent long‐term double tag study facilitated estimation of the annual natural mortality. Subsequent fish‐down of the population suggests that, in all likelihood, the carp have been eradicated from the lake, providing an unprecedented opportunity to verify the forward population estimates carried out in 1998. Results suggest that all three estimates were close to the true population size, with the reverse‐Schnabel estimate being the most accurate and within 1% of the true population in this relatively large lake (～2365 ha). Greater accuracy of the reverse‐Schnabel approach can be attributed to either minimised fish behavioural (i.e. gear susceptibility or avoidance) or computational bias associated with the forward‐Schnabel and Petersen approaches, respectively. While the original estimates served as a guide in eradication of carp from the lake, the ultimate validation provides a reliable framework for abundance estimation of this invasive fish in relatively large water bodies elsewhere.     

Further observations on limnetic zooplankton in a small lake and two enclosures containing fish

SUMMARY. In a small lake (Blelham Tarn, English Lake District) two plastic cylinders, each of which extends from the lake surface to the bottom sediments and encloses 18 000 m³ of water, were used to investigate effects of enclosure on the zooplankton. This paper describes observations from March 1973 to October 1974 and is the second part of a report on a project spanning 4 years.
Seasonal population densities of the more abundant species were essentially similar to those observed in the first part of the project, despite large changes in algal and predator populations. In the enclosures, fish (mostly Perca fluviatilis ) populations are known from observations by divers to have been large in the period under consideration and small in the first part of the project. Populations of Chaoborus larvae in the enclosures were small at all seasons from March 1973 to October 1974.     

Effects of an artificial protection structure on the sandy shore macrofaunal community: the special case of Lido di Dante (Northern Adriatic Sea)

Biomanipulation of eutropicated peaty lakes has rarely been successful; clear water with dense macrophyte stands fails to develop in most cases. It was unclear whether (1) high turbidity due to resuspension by benthivorous fish or wind is the major cause of low macrophyte density or whether (2) the establishment of submerged macrophyte stands is prevented by a lack of propagules, low cohesive strength of the lake sediment, high concentrations of phytotoxics, grazing by waterfowl and/or shading by periphyton growth. These hypotheses were tested in an experiment in a shallow peat lake in the Netherlands (Terra Nova). Removal of fish from a 0.5 ha experimental site resulted in clear water and the development of a dense (90% coverage) and species-rich (10 species) submerged vegetation. At a fish-stocked site and a control site the water remained turbid and dense macrophyte stands did not develop. The establishment of submerged macrophytes appeared not to be limited by a lack of propagules. Introduced plants grew poorly in turbid water, but very well in clear water. Exclosures showed that bird grazing reduced the plant biomass. In clear water grazing seemed to enhance the vegetation diversity. Periphyton development did not prevent plant growth in clear water. After the experiment, the fish stock was greatly reduced in the whole lake (85 ha), to test if (3) in a large lake, submerged macrophyte stands will not develop after biomanipulation. In the first season after fish reduction, transparency increased and species-rich submerged macrophyte stands developed, covering 60% of the shallow parts of the lake. Most of the species known to have occurred in the past re-established. The results indicate that high turbidity caused by benthivorous fish in combination with bird grazing were the major causes of the absence of submerged macrophyte stands in this lake. Abiotic conditions after the clearing of the lake were suitable for the growth of macrophytes. We infer that the restoration potential of submerged macrophyte stands in eutrophicated peaty lakes can be high, and results can be obtained quickly.     

River‐lake migration of fishes in the Dongting Lake area of the Yangtze floodplain

Over the past few decades, fish resources have declined severely owing to the river–lake disconnection within the Yangtze River floodplain. Studies on fish migrations between rivers and floodplain waters are imperative for fish resources restoration and lake management. However, few studies have as yet documented the migration rhythms of river–lake migratory fishes. Monthly investigations of the fish assemblage structure were conducted in three regions of the Dongting Lake, which is connected to the Yangtze River. Main results were: (i) Fish catches varied greatly, depending on the water level and area of the lake; (ii) Ten river–lake migratoty species were caught during the study, 80% of these during July–October when the water level was high. Species richness and relative abundance both decreased with increasing distance from the river, and the timing of peak abundance occurred later in the year; (iii) Abundance of grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix) peaked in July and August and were mainly composed of 0 + fishes. The results revealed that the key time for migration into the lake is July–August. Combining the results from previous studies, a comprehensive view is given of migration patterns of four domestic Chinese carps; (iv) Brass gudgeon (Coreius heterodon), appeared to migrate into the Dongting Lake as two separate shoals, differentiated by body size. They also appeared to remain close to the lake mouth area. Based on the above results, two recommendations can be made for river–lake migratory fish conservation in the Yangtze floodplain: prolonging the current fishing ban period of April–June to April–September; and opening sluice gates for as long as possible during April–September in order to maximize the opportunities for fish migration.     

Integrated aquaculture in Chinese lakes and paddy fields

While pond culturing is still the staple of Chinese freshwater fisheries, its extensive development is handicapped by the increasing shortage of land resource for cereal production in face of China’s population growth. Accordingly, people have looked towards the development of aquaculture in lakes (and reservoirs) in the 1970s. This paper reviews the successful integrated measures taken in an experiment for raising fish in Donghu lake (East lake) of Wuhan. By way of (1) stocking the right kinds of fish; (2) producing a large number of sizeable fingerlings; (3) improving fish screens; (4) controlling predatory fish; and (5) applying the ‘driving and concentrating’ bulk harvesting fishing method, fish production of the lake has increased steadily from 180 t in 1971 to 800 t in 1978, and then to 1840 t in 1995, all in an area of 1500 ha, and all without any supplementary feeding. Integrated aquaculture in paddy fields, known to be beneficial to both rice and fish production, has been regaining momentum in recent years. The paper summarizes its underlying principle, its benefits—economical, social and ecological—and the prospect of its development in China.     

Influence of fish assemblage and shallow lake productivity on waterfowl communities in the Boreal Transition Zone of western Canada

1. Shallow lakes in the Boreal Transition Zone (BTZ) in Alberta, Canada are naturally productive systems that provide important breeding and moulting habitat for many waterfowl (Anseriformes). To examine the relative importance of biotic and abiotic factors on waterfowl population densities, species richness and community composition, we surveyed 30 shallow lakes and evaluated the relationships among fish communities, lake characteristics and waterfowl in both breeding and moulting habitat. Shallow lakes were either fishless (n = 15), contained only small‐bodied fishes (n = 10) or contained large‐bodied, mostly predatory, fish in addition to small‐bodied fish (n = 5). 2. Environmental factors, including water colour, submerged aquatic vegetation, lake area and potassium, explained 24.3% of the variation in breeding waterfowl communities. Fish assemblage contributed independently to a small but significant proportion (13.4%) of the variation, while 13.8% of the explained variation was shared between environmental factors and fish assemblage. In total, 51.5% of the variation in breeding waterfowl communities was explained. 3. Overall, 55.5% of the total variation in moulting waterfowl communities was explained. Environment alone [especially total phosphorus, lake area, maximum depth and dissolved organic carbon (DOC)] and variation shared by fish and environment similarly accounted for most of the explained variation in moulting waterfowl communities (21.7% and 25.7% respectively), while fish assemblage was only one‐third as important (8.1%). 4. Both breeding and moulting waterfowl densities increased with lake productivity, even in eutrophic and hypereutrophic lakes. Breeding waterfowl density was also twice as great in fishless lakes than in lakes with fish, after accounting for lake area. 5. Certain waterfowl taxa were linked to fishless lakes, especially in the moulting season. Canvasback and moulting ring‐necked ducks were linked to small‐bodied fish lakes, whereas moulting common goldeneye were indicators of large‐bodied fish lakes. Knowledge of fish presence and species composition can therefore help guide conservation and management of waterfowl habitat in western Canada. Our results suggest that management efforts to maintain the most productive waterfowl habitat in the BTZ should focus on smaller, shallow, fishless lakes, particularly given that larger fish‐bearing systems have greater regulatory protection.     

青菱湖中长春鳊生物学的研究

1983-1985年对通长江的青菱湖中长春鳊的年龄与生长、食性、繁殖及其鱼群江湖交流等生态习性进行了调查。发现相当部分标本的鳞片上有明显的幼轮标志;性成熟后,雌鱼的生长较雄鱼迅速;摄取的食物种类与湖中各种水生植物的季节性盛衰相适应,但有一定的选择性;亲鱼能在湖中成熟产卵,但鱼卵因受自然条件限制,不能发育成活。湖中鱼群的补充仍依靠数量不定的1龄幼鱼由长江干流逆水或顺水伺机窜入湖内。江湖之间闸门的启闭主要根据农田水利的需要,因此,长春鳊鱼群规律性的江湖交流仍然受到阻碍。       

Mitochondrial and Allozyme Genetics of Incipient Speciation in a Landlocked Population of Galaxias Truttaceus (Pisces: Galaxiidae)

Galaxias truttaceus is found in coastal rivers and streams in south-eastern Australia. It spawns at the head of estuaries in autumn and the larvae spend 3 months of winter at sea before returning to fresh water. In Tasmania there are landlocked populations of G. truttaceus in a cluster of geologically young lakes on the recently glaciated Central Plateau. These populations have no marine larval stage and spawn in the lakes in spring. Speciation due to land locking is thought to be a frequent occurrence within Galaxias. To investigate the nature of the speciation event which may be occurring within lake populations of G. truttaceus we studied the mitochondrial DNA (mtDNA) and allozyme diversity of both lake and stream populations. Using the presence or absence of restriction sites recognized by 13 six-base restriction endonucleases, we found 58 mtDNA haplotypes among 150 fish collected from 13 Tasmanian and one south-east Australian mainland stream populations. The most parsimonious network relating the haplotypes by site loss or gain was starlike in shape. We argue that this arrangement is best explained by selection upon slightly beneficial mutations within the mitochondrial genome. Gene diversity analysis under Wright's island model showed that the populations in each drainage were not genetically subdivided. Only two of these stream haplotypes were found among the 66 fish analyzed from four lake populations. Despite the extreme lack of mtDNA diversity in lake populations, the observed nuclear DNA heterozygosity of 40 lake fish (0.10355) was only slightly less than that of 82 stream fish (0.11635). In the short time (3000-7000 years) that the lake fish have been landlocked, random genetic drift in a finite, stable-sized population was probably not responsible for the lack of mtDNA diversity in the lake populations. We infer the lake populations have probably experienced at least one, severe, but transitory bottleneck possibly induced by natural selection for life-history characters essential for survival in the lacustrine habitat. If speciation is occurring in the landlocked populations of G. truttaceus, then it may be driven by genetic transilience.     

A synopsis of lake sturgeon management in Alberta, Canada

The lake sturgeon ( Acipenser fulvescens ) is resident in the North and South Saskatchewan rivers of Alberta. Because of their confined distribution, low abundance, and vulnerability to anthropogenic impacts, lake sturgeon in Alberta have been the focus of specific management actions for nearly 60 years.
Lake sturgeon harvest was prohibited in Alberta from 1940 to 1968, after which a limited harvest was again permitted, but only as a hook-and-line sport fishery. After being reopened the fishery was primarily managed as a "trophy" fishery. Sport fishery harvest statistics have been compiled annually since 1968, through mail-out questionnaires sent to all holders of sturgeon angling licenses.
Few research studies have been undertaken on the life history or habitat requirements of lake sturgeon in the province, and biologists have relied primarily on anglers to provide information for management decisions. Preliminary population information for the South Saskatchewan River, from mark-recapture data, suggests a population size of about 3700 fish. Recent studies in the North Saskatchewan River indicate a population of about 1300 fish. Studies indicate that a portion of the population in both rivers is trans-boundary, moving between the waters of the adjoining provinces of Alberta and Saskatchewan, and creating concerns because of differences in angling regulations. During recent decades, major consumptive uses of water have also contributed to depletion of lake sturgeon habitat in the province.
After reviewing past management strategies and actions, Alberta Environmental Protection implemented a number of regulatory changes in 1987 to further protect lake sturgeon populations in the province while continuing to provide angling opportunities and maintaining a controlled harvest.     

Proposed methods and endpoints for defining and assessing adverse environmental impact (AEI) on fish communities/populations in Tennessee River reservoirs

Two multimetric indices have been developed to help address fish community (reservoir fish assemblage index [RFAI]) and individual population quality (sport fishing index [SFI]) in Tennessee River reservoirs. The RFAI, with characteristics similar to the index of biotic integrity (IBI) used in stream fish community determinations, was developed to monitor the existing condition of resident fish communities. The index, which incorporates standardized electrofishing of littoral areas and experimental gill netting for limnetic bottom-dwelling species, has been used to determine residential fish community response to various anthropogenic impacts in southeastern reservoirs. The SFI is a multimetric index designed to address the quality of the fishery for individual resident sport fish species in a particular lake or reservoir[4]. The SFI incorporates measures of fish population aspects and angler catch and pressure estimates. This paper proposes 70% of the maximum RFAI score and 10% above the average SFI score for individual species as "screening" endpoints for balanced indigenous populations (BIP) or adverse environmental impact (AEI). Endpoints for these indices indicate: (1) communities/populations are obviously balanced indigenous populations (BIP) indicating no adverse environmental impact (AEI), or are "screened out"; (2) communities/populations are considered to be potentially impacted; and (3) where the resident fish community/population should be considered adversely impacted. Suggestions are also made concerning how examination of individual metric scores can help determine the source or cause of the impact.     

A model study on the role of wetland zones in lake eutrophication and restoration

Shallow lakes respond in different ways to changes in nutrient loading (nitrogen, phosphorus). These lakes may be in two different states: turbid, dominated by phytoplankton, and clear, dominated by submerged macrophytes. Both states are self-stabilizing; a shift from turbid to clear occurs at much lower nutrient loading than a shift in the opposite direction. These critical loading levels vary among lakes and are dependent on morphological, biological, and lake management factors. This paper focuses on the role of wetland zones. Several processes are important: transport and settling of suspended solids, denitrification, nutrient uptake by marsh vegetation (increasing nutrient retention), and improvement of habitat conditions for predatory fish. A conceptual model of a lake with surrounding reed marsh was made, including these relations. The lake-part of this model consists of an existing lake model named PCLake. The relative area of lake and marsh can be varied. Model calculations revealed that nutrient concentrations are lowered by the presence of a marsh area, and that the critical loading level for a shift to clear water is increased. This happens only if the mixing rate of the lake and marsh water is adequate. In general, the relative marsh area should be quite large in order to have a substantial effect. Export of nutrients can be enhanced by harvesting of reed vegetation. Optimal predatory fish stock contributes to water quality improvement, but only if combined with favourable loading and physical conditions. Within limits, the presence of a wetland zone around lakes may thus increase the ability of lakes to cope with nutrients and enhance restoration. Validation of the conclusions in real lakes is recommended, a task hampered by the fact that, in the Netherlands, many wetland zones have disappeared in the past.     

The consequences of a drastic fish stock reduction in the large and shallow Lake Wolderwijd,The Netherlands. Can we understand what happened?

In 1990 an experiment started in the large and shallow lake Wolderwijd (2700 ha, mean depth 1.5 m) to improve the water quality. About 75% of the fish stock was removed (425 000 kg fish). The fish was mainly composed of bream and roach. In May 600000 young pikes (3–4 cm) were introduced.In May 1991 the water became very clear (Secchi depth 1.8 m) during a spring bloom of large Daphnia. Then the grazing by zooplankton was eight times higher than the primary production of algae and the total suspended matter concentration became very low. Compared to the situation before the fish reduction, the grazing had increased only slightly, while the primary production had decreased significantly in early spring. The fish stock reduction might have contributed to the reduction in primary production by a reduced internal nutrient load. The clear water period lasted six weeks. Daphnia disappeared in July due to food limitation, the algal biomass increased and the Secchi depth became 50 cm. Daphnia did not recover during summer, due to predation that was not caused by 0 + fish but by the mysid shrimp Neomysis integer. Neomysis could develop abundantly, because of the reduced biomass of the predator perch. The production of young fish had been low because of the cold spring weather. The cold weather was probably also responsible for the slow increase in density of macrophytes. After 1991, perch probably can control Neomysis. Due to lack of spawning places and shelter for 0 + pike, pike was probably not able to control the production of 0 + fish. In a lake of this scale, it will not be easy to get more than 50% coverage of macrophytes, which seems necessary to keep the algal biomass low by nutrient competition. Therefore, we expect also in the future a decrease in transparency in the summer. Locally, especially near Characeae, the water might stay clear.     

Does the burbot,Lota lota,have rest years between normal spawning seasons?

A large number of sterile burbot ( Lota lota ) have been recorded on the northern coast of the Bothnian Bay (29–93%) and in Lake Kemijärvi in northern Finland (44%). A suggested hypothesis is that the burbot needs one or more rest years between spawning seasons to restore the fat reserves in its liver. A comparison made here between the three burbot populations (brackish water, lake and river), did not confirm this hypothesis. The somatic condition index, liver index and intestine index of the normally-spawning river burbot, in which the percentage of non-spawning fish was 14%, were considerably lower than those in spawned or sterile coastal or lake burbot, so that poor nutrition state did not result in sterility or rest years.     

Documentation of lake sturgeon (Acipenser fulvescens Rafinesque, 1817) recovery and spawning success from a restored population in the Mississippi River,Missouri, USA

Lake sturgeon Acipenser fulvescens are considered rare and were nearly extirpated in the Mississippi River in Missouri by 1931 as a result of overfishing and habitat fragmentation. Propagation efforts have been implemented by the Missouri Department of Conservation since 1984 as means to restore the lake sturgeon population. Although recent population increases have been observed, a formalized evaluation to determine if lake sturgeon are self‐sustaining in the Missouri portion of the Mississippi River has not been completed. Therefore, the objectives of this study were to: (i) determine the proportion of reproductive individuals, (ii) evaluate seasonal movement patterns of adults, and (iii) validate purported spawning locations within the Mississippi River in Missouri. Lake sturgeon catch data indicated that approximately 11 percent of the population are reproductively mature. Additionally, telemetry data confirms that the greatest movement by adult lake sturgeon occurs during spring, which suggests spawning behavior. Finally, it was possible to document lake sturgeon embryos and emergent fry larvae below Melvin Price Locks and Dam 26 in the Upper Mississippi River near St. Louis, Missouri. Water velocity, depth, and substrate size were measured at this location and embryos were collected and hatched in the laboratory. River gage data suggest that spawning behavior may have been elicited by a large influx of water during a drawdown period of water above the dam. This study represents the first documented spawning of A. fulvescens in the Mississippi River and highlights the success of recovery efforts in Missouri.     

The Relationship between the Distribution of Common Carp and Their Environmental DNA in a Small Lake

Although environmental DNA (eDNA) has been used to infer the presence of rare aquatic species, many facets of this technique remain unresolved. In particular, the relationship between eDNA and fish distribution is not known. We examined the relationship between the distribution of fish and their eDNA (detection rate and concentration) in a lake. A quantitative PCR (qPCR) assay for a region within the cytochrome b gene of the common carp (Cyprinus carpio or ‘carp’), an ubiquitous invasive fish, was developed and used to measure eDNA in Lake Staring (MN, USA), in which both the density of carp and their distribution have been closely monitored for several years. Surface water, sub-surface water, and sediment were sampled from 22 locations in the lake, including areas frequently used by carp. In water, areas of high carp use had a higher rate of detection and concentration of eDNA, but there was no effect of fish use on sediment eDNA. The detection rate and concentration of eDNA in surface and sub-surface water were not significantly different (p≥0.5), indicating that eDNA did not accumulate in surface water. The detection rate followed the trend: high-use water > low-use water > sediment. The concentration of eDNA in sediment samples that were above the limit of detection were several orders of magnitude greater than water on a per mass basis, but a poor limit of detection led to low detection rates. The patchy distribution of eDNA in the water of our study lake suggests that the mechanisms that remove eDNA from the water column, such as decay and sedimentation, are rapid. Taken together, these results indicate that effective eDNA sampling methods should be informed by fish distribution, as eDNA concentration was shown to vary dramatically between samples taken less than 100 m apart.