Genetic diversity and structure of lake whitefish (Coregonus clupeaformis) 100 years after closure of the commercial fishery

In small, inland fisheries even small perturbations to the ecosystem can quickly influence population abundance, size and age distribution, and genetic structure and diversity. In Lake Champlain, lake whitefish (Coregonus clupeaformis) experienced extensive commercial harvest from the mid-1800 s to1918 and habitat fragmentation due to the construction of multiple causeways between 1850 and 1899. We evaluated the influence these environmental perturbations had on lake whitefish population genetics 120 years later. We used historic catch records to determine whether fishing pressure could have been strong enough to reduce lake whitefish population abundance, and used genotype data from eight microsatellite loci to look for genetic signatures of population-sub structure and bottleneck. Catch records indicate lake whitefish were being harvested in Lake Champlain at a similar magnitude to the Great Lakes, and simulations suggest genetic diversity may have been lost as a result of harvest. However, we were unable to detect significant evidence of a genetic bottleneck, but we cannot conclusively suggest that harvest of lake whitefish did not result in a genetic bottleneck. Additionally, we found only slight evidence of population sub-structure among isolated basins, suggesting that either some gene flow among basins is possible, or that populations are just beginning to diverge and therefore differences in allele frequency were too small to detect. These data provide a perspective on effects of an inland lake commercial fishery that was closed prior to population collapse, and offer a comparison to the Laurentian Great Lakes where lake whitefish are still being harvested.     

Spatial and temporal variation in distribution of larval lake whitefish in eastern Lake Ontario: Signs of recovery?

The lake whitefish (Coregonus clupeaformis) is one of the native Lake Ontario fishes that declined severely over the past century. Recent evidence of larval lake whitefish production in a historic spawning area (Chaumont Bay) might signal a recovery of this species in New York waters. We surveyed coastal and open water areas to evaluate densities and estimate total abundance of larval lake whitefish in Chaumont Bay. Other historic spawning areas and embayments with appropriate spawning and nursery habitat were also surveyed, but only a few larvae were found outside of Chaumont Bay. Lake whitefish larvae were found in every embayment sampled within Chaumont Bay, with larval densities of nearly 600/1000 m² in some samples. Greatest abundances occurred in the northern sectors and near the mouth of the bay. Open water densities were generally less than half that of nearshore sites. The total bay-wide estimate for 2005 was approximately 644,000 lake whitefish larvae, but dropped to 230,000–400,000 in 2006 and 2007, respectively. Mean larval growth rates (0.36 mm/day) did not differ by year, but were consistently higher in early May than in late April. Lake whitefish production in Chaumont Bay is encouraging for this species, but the cause and persistence of the decline after 2005 can be determined only by continued monitoring. Other possible bottlenecks of survival may exist at juvenile and adult stages and could significantly affect recruitment dynamics. This species is sensitive to normal climatic fluctuations and increased variability associated with global climatic change could make winter nursery conditions unfavorable for this species.     

Does hatchery rearing of lake trout affect their reproductive behavior in the wild?

Stocking of hatchery-reared fishes has been used with variable success as a management action to promote the recovery of populations and species. The practice has been controversial for several reasons, including uncertainty about whether the hatchery rearing experience may affect reproduction after release. Fine-scale acoustic telemetry was used during three spawning seasons to test whether hatchery rearing affects the reproductive behavior of lake trout using a spawning shoal complex in northern Lake Huron. Within sex, wild- and hatchery-reared fish behaved similarly, but significant behavioral differences occurred between sexes. Lake trout of both sexes moved synchronously onto the spawning shoals at the completion of autumn thermal turnover and occupied the same spawning sites (confirmed visually by presence of fertilized eggs) on the shoals. Male lake trout tended to congregate directly on spawning sites, with duration of occupancy varying greatly among years. Female lake trout spent less time on spawning shoals than males and congregated less at spawning sites on shoals. Most fish visited multiple spawning sites among shoals per season, with many making multiple transits among individual spawning sites. We found no evidence to support the hypothesis that hatchery rearing impairs spawning behavior of lake trout and, therefore, conclude that behavior deficiencies on the spawning ground are likely not an impediment to rehabilitation of lake trout in northern Lake Huron. Our study narrows the field of possible impediments to lake trout rehabilitation in the Great Lakes and provides insights that expand the conceptual model of lake trout spawning behavior.     

What controls distribution of larval and juvenile yellow perch? The role of habitat characteristics and spatial processes in a large,shallow lake

The goal of this study was to determine the relative contribution of environmental and spatial processes governing the distribution of larval and juvenile yellow perch (Perca flavescens) in two shallow embayments of a large fluvial lake on the St. Lawrence River system. We tested the hypotheses that: i) larval distribution is not related to habitat characteristics, presumably due to their relatively low swimming capacity, whereas ii) these environmental variables drive juvenile distribution, reflecting a more active habitat selection. This study is one of the first attempts to partition the relative roles of environmental and spatial factors in shaping the distribution of a freshwater fish through its early ontogeny. We show that larvae were not spatially aggregated within the embayments and that habitat characteristics, mainly related to aquatic vegetation, played an important role in explaining their distribution. In contrast, juvenile abundances were not significantly related to habitat characteristics, despite being spatially structured over multiple scales. Contrary to our predictions, habitat association was stronger for larvae than for juveniles which were aggregated independent of habitat characteristics. Increased swimming capacities may thus facilitate the aggregation of juveniles rather than strengthening their association with habitat, at least at the scales considered here (ca 3 km²). These results shed a new light on the factors governing larval and juvenile yellow perch distribution, suggesting that active habitat choice might begin earlier than previously thought.     

Giardia and Cryptosporidium in source waters of S?o Paulo State, Brazil.

Giardia lamblia and Cryptosporidium parvum are two protozoan intestinal parasites responsible for many drinking-water-related disease outbreaks in recent years. They are very resistant to conventional water treatment processes, can persist for long times in the environment and are, therefore, of great concern for public health. This work aimed to evaluate the presence of Giardia and Cryptosporidium in water sources from S?o Paulo State, Brazil, as part of the "Evaluation of Inland Waters from S?o Paulo State" project from CETESB. Over a period of 19 months, 278 water samples from 28 sites located in 10 watersheds were analysed. The immunofluorescence assay was used after concentration of the samples by the calcium carbonate flocculation technique. Thermotolerant (faecal) coliforms, faecal streptococci and Clostridium perfringens were also determined in order to verify the existence of correlation between these bacterial indicators and the protozoa. Giardia and Cryptosporidium were detected in 27% and 2.5% of the samples, respectively, a lower figure compared with the results reported by other authors, especially for Cryptosporidium. A Spearman rank correlation test demonstrated a significant correlation between Giardia and faecal indicator concentrations. According to the American Regulation of Monitoring (ICR), treated water from 16 of these 28 collection sites should also be analysed to evaluate whether the treatment process could remove the parasites. Some technical deficiencies of these methods still limit the utilisation of the monitoring results for public health decisions, but the data here reported will help to improve the quality of drinking water in S?o Paulo State.     

Relationship between lake trout spawning,embryonic survival,and currents: A case of bet hedging in the face of environmental stochasticity?

Lake trout, Salvelinus namaycush, spawning in the Great Lakes occurs primarily on cobble substrate at relatively shallow water depths that can experience strong water currents. Strong currents may limit embryonic survival by damaging or displacing eggs, but may also reduce the accumulation of fine material and limit foraging by potential egg predators. To better understand the importance of currents, we evaluated the role of currents in spawning habitat selection, egg density and survival, and egg predator density at a spawning reef in Lake Champlain (USA). Most spawning occurred one week after the largest storm event associated with the strongest currents and greatest upwelling. Highest spawning activity was associated with a relatively shallow part of the reef that had the highest current velocity and greatest potential for egg displacement. Within the interstices, the survival of naturally deposited eggs was unrelated to the concurrent loss of artificial eggs. We propose that the reproductive strategy of spawning on shallow areas of a reef that have the highest current velocity and high potential for egg loss represents a type of bet hedging to optimize survival of those embryos that remain within interstices. This strategy may have evolved in response to environmental stochasticity that resulted in higher egg survival.     

Spatial and seasonal variation in the phytoplankton community of Lake Victoria’s Mwanza Gulf,compared to northern parts of the lake

We investigated the phytoplankton species composition and abundance in two seasons in Mwanza Gulf, Lake Victoria (Tanzania). Phytoplankton was sampled and chlorophyll a content was measured in the dry and wet seasons of 2010–2011 at three stations, from the southern land-inward end of the Gulf towards the open lake. Cyanobacteria, mostly small colonial and filamentous species (e.g., Aphanocapsa spp., Planktolyngbya spp., Merismopedia spp.) dominated at each station (76–95 %), followed by Chlorophyta (5–21 %), whereas the contribution of Bacillariophyceae was small (0–6 %). Phytoplankton densities were generally higher in the rainy season and strongly increased going land-inward from the open lake. Low abundance of N-fixing phytoplankton species suggests that N-fixation was low. The chlorophyll a content in the mouth of the Gulf was low (mean values 4–6 µg/L) compared to values reported previously. Also, chlorophyll a values (means 11–14 µg/L) at land-inward stations of Mwanza Gulf were much lower than those in the northern gulfs (Napoleon Gulf, Murchison Bay and Nyanza Gulf). Between 2002 and 2009 the phytoplankton composition of Mwanza Gulf changed from a community mostly dominated by Bacillariophyceae into a community dominated by Cyanobacteria. In the open water of Lake Victoria, Bacillariophyceae and Cyanobacteria were both abundant. Cyanobacteria dominated both in the three northern gulfs and Mwanza Gulf, but all four showed substantial differences in species and genus compositions. Phytoplankton composition and abundance in Mwanza Gulf differs in many respects from the open water of Lake Victoria and its three northern gulfs.     

Trends in the distribution and abundance of Hexagenia spp. in Saginaw Bay,Lake Huron, 1954–2012: Moving towards recovery?

Since at least the 1940s, multiple anthropogenic disturbances to the Laurentian Great Lakes have had detrimental effects on benthic habitats and biota including decimating the environmentally sensitive burrowing mayfly genus Hexagenia around the mid-1950s. While remediation efforts have facilitated recovery of some populations, benthic surveys in Saginaw Bay, Lake Huron in the last 50 years have only occasionally discovered Hexagenia nymphs. Recently, adult Hexagenia swarms have been reported near the bay; therefore, we corroborated the local presence of Hexagenia adults and evaluated the current status of Saginaw Bay Hexagenia nymphs. We quantified adults during mayfly emergence events in 2010 at three Tawas City, Michigan, USA area locations, and found > 17 Hexagenia/m²/site. We quantified nymphs from Ponar grab samples collected at 57 sites in Saginaw Bay between 2009 and 2012, and found 1.5 nymphs/m² overall with nymphs present at 15.8% of sites sampled, their greatest documented distribution in Saginaw Bay since 1956. Additionally, we mapped bay sediment composition and related sampling site abiotic conditions with both Hexagenia presence and abundance using Zero-Inflated Poisson regression. Model results indicate that the probability of observed Hexagenia absence being true absence is positively related to both sediment sandiness and surficial dissolved oxygen concentration while Hexagenia abundance is greatest where surficial temperatures are ~ 18.6 °C and is also related to sediment sand content. The documentation of nearby adults and in bay nymphs may indicate the beginning of a Hexagenia return to Saginaw Bay, and, therefore, a possible improvement of the ecosystem's benthic health.     

Can Sub-Saharan Africa feed itself? The role of irrigation development in the region’s drylands for food security

ABSTRACT

This paper assesses the potential role of investments in irrigation in Sub-Saharan Africa in improving food security and self-sufficiency in the region. Focusing on the region’s drylands, the study identifies a potential for expanded irrigated area of 6–14 million hectares (ha), depending on technology costs and other factors. Linkage of these results with a global agricultural trade model shows that accelerated irrigation investment can effectively reduce growing food import dependency from 54% under a business-as-usual scenario to a much smaller 17–40%; and can also reduce the population at risk of hunger and child under-nutrition.     

Assessing Assessment: Can the Expected Effects of the St. Marys River Sea Lamprey Control Strategy Be Detected?

In 1997 the Great Lakes Fishery Commission approved a 5-year (1998 to 2002) control strategy to reduce sea lamprey (Petromyzon marinus) production in the St. Marys River, the primary source of parasitic sea lampreys in northern Lake Huron. An assessment plan was developed to measure the success of the control strategy and decide on subsequent control efforts. The expected effects of the St. Marys River control strategy are described, the assessments in place to measure these effects are outlined, and the ability of these assessments to detect the expected effects are quantified. Several expected changes were predicted to be detectable: abundance of parasitic-phase sea lampreys and annual mortality of lake trout (Salvelinus namaycush) by 2001, abundance of spawning-phase sea lampreys by 2002, and relative return rates of lake trout and sea lamprey wounding rates on lake trout by 2005. Designing an effective assessment program to quantify the consequences of fishery management actions is a critical, but often overlooked ingredient of sound fisheries management.     

Can native species compete with valuable exotics? Valuing ecological changes in the Lake Michigan recreational fishery

The Chinook salmon population in Lake Michigan is declining precipitously due to ecological changes, and the impact on recreational fishing value is unknown. We estimate a conditional logit model to characterize how Wisconsin resident anglers react to changes in species-specific availability and catch rates. Using these results, we calculate the non-market value of access to the fishery that reflects current, historical, and potential future fishing conditions. We then predict whether native lake trout and walleye, which are more resilient to the changing conditions in the lake, can maintain the fishery’s value if non-native Chinook salmon collapses. Results show that while large losses would occur absent other improvements, a portion of the fishery’s value could be maintained if substitute species, particularly walleye, improved in quality and were readily accessible.     

Sleeping with the enemy? Capturing internal risks in the logical framework of a water management project

Logframes are fundamental to contemporary development. However, there are ongoing debates about their efficacy. This paper pinpoints the limitations of the logframe approach in a water project in Central Asia. Issues surrounding logframes are identified. These include addressing internal risks; the use of baseline studies for the accuracy of assumptions; the ability to adapt under an inflexible budget; and linking the logframe and contract. Findings show that rigid planning may constrain effective project implementation. Greater flexibility through embedded learning and adaptation, adjustable budgets and meaningful mainstreaming of risks may equip projects to cope with uncertainties to achieve sustainability.     

Are hydropower and irrigation development complements or substitutes? The example of the Nam Ngum River in the Mekong Basin

Hydropower and irrigation developments to address rising demand for food and energy are modifying the water balance of the Mekong Basin. Infrastructure investment decisions are also frequently made from a sub-catchment perspective. This paper compares river flows with irrigation development stages in the Nam Ngum sub-basin where the potential for irrigation and hydropower expansion is largely untapped. It shows that full hydropower development in this basin allows irrigation water use to triple, even as it reduces competition with environmental flow requirements. The implications for the wider Mekong are, however, unclear, particularly given uncertainty over parallel transformations elsewhere in the basin.     

Patterns of long-term dynamics of aquatic communities and water quality parameters in the Great Lakes: Are they synchronized?

Long time series data can provide insights into dynamics of large lakes. We use the USEPA-GLNPO biological monitoring dataset (phytoplankton, benthos, zooplankton and water quality), collected from 1996 through 2016, to identify whether there is evidence of concordant linear or non-linear trends in community composition, density/biomass/biovolume and major environmental parameters. We show changes in biotic assemblages and water quality variables, particularly in Lakes Michigan and Huron. These include changes in phytoplankton biovolume and zooplankton biomass, increasing invasive Dreissena abundance and decreasing densities of other benthos. Biotic changes are accompanied by pronounced changes in water quality and nutrient ratios. Species change-points, identified using threshold indicator taxon analysis, are often less abrupt, but there are clear shifts in a large proportion of species in each assemblage. The concordance of breakpoints among assemblages or lack thereof provides valuable insight into potential drivers of ecosystem change.     

What factors affect the suspended sediment concentrations in rivers? A study of the upper Warta River (Central Poland)

The suspended sediment concentration (SSC) of the Warta River was analysed using data collected at the Sieradz gauging station (Central Poland) during the period of 1961–1980. The aim of the study was to characterize the trend in the suspended sediment transported over this multi‐annual period and search for possible correlations between the suspended sediment values and the discharge and thermal seasonality factors. This study also investigated whether the SSC is affected by anthropogenic factors. The SSC in the river water increased over the analysed 20‐year period. It was caused mainly by the training works in the Warta valley upstream of Sieradz and the opening of the Be?chatów lignite mine. No direct relationship between the SSC and fluctuations in the discharge was noted. A connection existed between the SSC and ice phenomena on the river. The river ice breakup was often coincident with increases in SSC; however, the SSC increased rapidly during the freezing of the river. There was also a positive correlation between the SSC and the temperature of the water during the summer half‐year, which resulted from the growth of phytoplankton. This process was supported by the general warming trend observed in the river water and by an increase in the quantity of nutrients noted since the early 1970s. It is worth emphasizing that the relationships established between the SSC and the studied factors are not always unequivocal and repetitive. It follows that, as a rule, the SSC is influenced by more factors than are actually considered in this study.     

Difficulties of fishing at Lake Naivasha,Kenya: is community participation in management the solution?

Unlike other lakes in tropical regions, Lake Naivasha exhibits low fish species diversity. The fishery is based on introduced fish species that are not native to the lake. The lake ecosystem is very fragile, as reflected in its fluctuating fish catches. The fishery almost completely collapsed in 2001, due partly to mismanagement and ignorance about needed conservation measures. The Kenyan government, like many governments around the world, recognized the need to involve fishers and other stakeholders, in order to ensure better management of the lake fisheries resources. Also referred to as collaborative management (co-management), this management approach provides the opportunity to share responsibility for managing the fishery resources between the government and the community. A total ban on fishing was imposed in February 2001, lasting for 1 year, to allow lake fish stocks to recover. This study analyses the co-management process for Lake Naivasha, and discusses the role played by the community during the fishing ban, as well as the successes and challenges encountered, and the tribulations and perceptions of the fishers regarding the new management strategy. It also comprises the first documentation of community participation in fisheries management begun for Lake Naivasha in the year 2001.     

Is glyphosate an underlying cause of increased dissolved reactive phosphorus loading in the Western Lake Erie basin?

The western Lake Erie basin has been experiencing increasing dissolved reactive phosphorus (DRP) loads since approximately 1994, the causes of which are not well understood. Changing agricultural practices such as no-till agriculture and tile drainage are certain to have an effect on DRP loads. This study examines glyphosate as a potential driver of the observed increase in the western Lake Erie basin DRP loads since 1994 by examining adoption of herbicide-tolerant crops, glyphosate use, and both DRP loads and concentrations from the mid-1990’s to the present. Glyphosate’s widespread usage contributes to DRP loadings and eutrophication in the western Lake Erie basin.     

Can we characterize river corridor evolution at a continental scale from historical topographic maps? A first assessment from the comparison of four countries

National historical map resources are assessed in four European countries to characterize river corridor features and associated channel changes, as well as identify issues limiting or promoting geomorphic assessment procedures at a continental scale. A geomorphic audit that launches potential data for diagnosis from reach to continental scales could offer a good resource for biology and ecology managers of river authorities or government agencies and engineers. The assessment compares the resources available by country in terms of period covered, spatial scale, history and chronology, and representation of the fluvial corridor features. We then applied the Historical Maps Vectorization Toolbox, initially developed for vectorizing river corridors from French maps, to detect and extract flow channels, unvegetated bars and riparian vegetation patches from historical topographical maps. We found that (a) it is difficult to apply an audit of channel changes to the whole continental scale because map legends differ between countries due to geographic and political specificity; (b) there exists an opportunity to get assessment information in all countries at reach or national scale where map resources are available; (c) the highest potential is observed in Switzerland and Belgium where there is high quality national map coverage from the 19th century; and (d) the algorithm Historical Maps Vectorization Toolbox applied to map resources works well with any of the countries, and its widespread application is encouraging.     

Return of adult anadromous allis shad (Alosa alosa L.) in the river Seine,France: A sign of river recovery?

In the past, the diadromous fish fauna of the river Seine comprised 11 native species. From the second part of the 19th century, the progressive modification of the river for navigation purposes and the increase of domestic and industrial pollution led to a general decline of migratory stocks and the extinction of several species. Among them, allis shad (Alosa alosa) was previously widespread in the Seine basin, but disappeared at the beginning of the 20th century. In July 2004, several individuals of shad were observed in the river Seine upstream of Paris (410 km from the sea), one of them was identified as an allis shad that had clearly spawned (thin fish and large scale erosion). A second allis shad was caught in a more downstream location (180 km from the sea) in November 2007 and a spawning mark was found on scales demonstrating clear evidence of reproduction. Recent occurrences of this species are discussed in relation to the present conditions of water quality and migration in the Seine watershed and recent evolution of the species' distribution in the northwestern part of France. Copyright © 2009 John Wiley & Sons, Ltd.     

Is reduced benthic flux related to the Diporeia decline? Analysis of spring blooms and whiting events in Lake Ontario

Benthic monitoring by USGS off the southern shore of Lake Ontario from October 1993 to October 1995 provides a detailed view of the early stages of the decline of the native amphipod Diporeia. A loss of the 1994 and 1995 year classes of Diporeia preceded the disappearance of the native amphipod at sites near Oswego and Rochester at depths from 55 to 130 m. In succeeding years, Diporeia populations continued to decline in Lake Ontario and were nearly extirpated by 2008. Explanations for Diporeia's decline in the Great Lakes include several hypotheses often linked to the introduction and expansion of exotic zebra and quagga mussels (Dreissena sp.). We compare the timeline of the Diporeia decline in Lake Ontario with trends in two sources of organic matter to the sediments — spring diatom blooms and late summer whiting events. The 1994–95 decline of Diporeia coincided with localized dreissenid effects on phytoplankton in the nearshore and a year (April 1994 to May 1995) of decreased flux of organic carbon recorded by sediment traps moored offshore of Oswego. Later declines of profundal (> 90 m) Diporeia populations in 2003 were poorly associated with trends in spring algal blooms and late summer whiting events.