Fish community changes after minimum flow increase: testing quantitative predictions in the Rhône River at Pierre-Bénite, France

1. Many aspects of the flow regime influence the structure of stream communities, among which the minimum discharge left in rivers has received particular attention. However, instream habitat models predicting the ecological impacts of discharge management often lack biological validation and spatial generality, particularly for large rivers with many fish species. 2. The minimum flow at Pierre‐Bénite, a reach of the Rhône river bypassed by artificial channels, was increased from 10 to 100 m³ s^?1 in August 2000 (natural mean discharge 1030 m³ s^?1), resulting in a fivefold increase in average velocity at minimum flow. Fish were electrofished in several habitat units on 12 surveys between 1995 and 2004. 3. Principal components analysis revealed a significant change in the relative abundance of fish species. The relative abundance of species preferring fast‐flowing and/or deep microhabitats increased from two‐ to fourfold after minimum flow increase. A change in community structure confirmed independent quantitative predictions of an instream habitat model. This change was significantly linked to minimum flow increase, but not to any other environmental variables describing high flows or temperature at key periods of fish life cycle. The rapidity of the fish response compared with the lifespan of individual species can be explained by a differential response of specific size classes. 4. The fish community at Pierre‐Bénite is in a transitional stage and only continued monitoring will indicate if the observed shift in community structure is perennial. We expect that our case study will be compared with other predictive tests of the impacts of flow restoration in large rivers, in the Rhône catchment and elsewhere.     

Simple predictions of instream habitat model outputs for target fish populations

1. Bottom-up approaches based on individual behaviour can help to identify key variables influencing populations at larger scales. Instream habitat models have been developed to predict the consequences, for populations in stream reaches, of fish preferences for particular hydraulic conditions observed at the scale of individuals. Conventional instream habitat models (e.g. PHABSIM) predict habitat values for species or life stages in reaches, and their changes with discharge. Despite their worldwide use, they have been subject to continuing criticism and have been mainly limited to site-specific case studies.
2. We ran conventional instream habitat models in 58 French stream reaches dominated by brown trout. Using non-linear mixed effect models, we demonstrated that the outputs of instream habitat models (habitat values for three trout life stages and five other species) are predictable from average characteristics of reaches (discharge, depth, width and bed particle size).
3. Our models closely reflect variations in habitat values within-reaches (with discharge) and between-reaches. Within-reach changes are linked to the Reynolds number of reaches, while between-reach changes depend mainly on the Froude number at median daily discharge. These two dimensionless variables combine discharge, mean depth and mean width of reaches. Independent model validations showed robust model predictions that are consistent with studies of habitat values for brown trout made in larger streams from western North America.
4. Our results contribute to identifying the main hydraulic variables governing estimates of fish habitat values. They should facilitate habitat studies in multiple streams, at the basin or larger scales, while reducing their cost. They should enhance the biological validation of habitat model predictions, which remains critical.     

Focusing environmental management budgets on non-linear system responses: potential for significant improvements to freshwater ecosystems

1. The non-linear responses of environmental systems to changes imposed upon them is well known to scientists. Environmental managers rarely act accordingly, however, because of communication problems, a lack of imagination and various other constraints. Therefore, we illustrate such non-linear responses to demonstrate that gains in efficiency (benefit per money spent) can be made by integrating these characteristics into decision making.
2. Identifying three measures that are currently the focus of large freshwater management budgets (waste-water treatment, riparian buffer strips and discharge allocations to regulated rivers), we relate the costs of these measures to the environmental improvements achievable in running waters. For each of these measures, the environmental improvement achieved per currency unit significantly decreases with an increase in total money spent.
3. Traditional environmental management ignores this system behaviour because it invests important parts of budgets in a particular measure before focusing on the next among other measures. We therefore advocate alternating investments in that measure which achieves the greatest environmental improvement in the next possible investment step. Compared with traditional management, this alternating decision-making strategy will achieve greater environmental improvements for a given total budget.     

Hypervariable Region of Human Immunoglobulin Heavy Chains

THE variable regions of human immunoglobulin light chains contain three areas of unusually high variability^1–4. Similar hypervariable regions have been postulated for human heavy chains^{5, 6}, but there are no amino-acid sequence data to support this idea. These hypervariable regions are particularly interesting because they may be the areas of the immunoglobulin molecule involved in antibody complementarity.We have made use of the recent observation that a variable region subclass of heavy chains is characterized by an unblocked amino-terminal residue⁷ and of the availability of automated sequencing techniques^{8, 9} to study this question in detail with additional heavy chain sequences.     

Quantifying the effects of temperature and flow regime on the abundance of 0+ cyprinids in the upper River Rhone using Bayesian hierarchical modelling

1. Assuming that recruitment variation is one of the main sources of fish population and assemblage changes, it is necessary to understand how natural variations in the environment influence 0+ fish abundance. Temperature regimes play an important role in enhancing both spawning activity and survival during early larval fish development. Flow regime variation, which is a powerful source of stream disturbance, is another factor to be taken into account. 2. Responses to these variables need to be assessed using long‐term datasets, since standard statistical approaches fail to provide a causal structure or to quantify the different effects. We therefore used a 26‐year dataset to evaluate the respective effects of seven derived independent variables describing the effects of temperature and flow regimes on the 0+ juvenile abundance of eight fish species in the River Rhone. 3. A clustering procedure using the Kendall tau rank correlation coefficient was implemented and identified three groups of fish according to their synchronic variations in juvenile abundance; i.e. varying with decreasing juvenile abundance, slightly increasing juvenile abundance and increasing juvenile abundance. These clusters provided the basis for building hierarchical log‐Poisson generalized linear models. The Bayesian paradigm gives a reliable framework for model selection, and the best model was determined using the Bayes Factor. 4. The posterior distribution of the regression parameters was coherent with what was expected based on knowledge of the biology of the different species. It indicates that temperature regime drives 0+ juvenile abundance but that flow regime also plays an important regulating role. The models thus detected evidence of the consequences of specific flow events such as larval drift and an increase in available habitat during higher flow discharges. 5. Our study illustrates the advantages of using a hierarchical modelling approach to quantify ecological effects by improving discrimination between the different sources of uncertainty, leading to better precision when estimating regression parameters.     

Enzymatic Probe for Accessibility of NH<Subscript>2</Subscript>-Terminal Residues in Immunoglobulins

ARGINYL-tRNA-protein transferase is a soluble enzyme from mammalian tissues which catalyses the transfer of arginine from arginyl-tRNA into peptide linkage specifically with NH₂-terminal aspartic or glutamic acid residues of protein acceptors^1,2. Molar equivalents of arginine are transferred to appropriate NH₂-terminal residues². The reaction differs in many respects from the transfer of amino-acids associated with protein synthesis de novo and is thought to be a mechanism for regulating the activity of acceptor proteins³. Many immunoglobulins possess aspartic or glutamic acid in the NH₂-terminal position and it was interesting to examine whether arginylation of such residues might result in an alteration of activity of these proteins, for there is considerable evidence that the antibody-combining site is contained in the NH₂-terminal region of both light^4–7 and heavy^8,9 chains.     

Focusing environmental management budgets on non-linear system responses: potential for significant improvements to freshwater ecosystems

1. The non-linear responses of environmental systems to changes imposed upon them is well known to scientists. Environmental managers rarely act accordingly, however, because of communication problems, a lack of imagination and various other constraints. Therefore, we illustrate such non-linear responses to demonstrate that gains in efficiency (benefit per money spent) can be made by integrating these characteristics into decision making.
2. Identifying three measures that are currently the focus of large freshwater management budgets (waste-water treatment, riparian buffer strips and discharge allocations to regulated rivers), we relate the costs of these measures to the environmental improvements achievable in running waters. For each of these measures, the environmental improvement achieved per currency unit significantly decreases with an increase in total money spent.
3. Traditional environmental management ignores this system behaviour because it invests important parts of budgets in a particular measure before focusing on the next among other measures. We therefore advocate alternating investments in that measure which achieves the greatest environmental improvement in the next possible investment step. Compared with traditional management, this alternating decision-making strategy will achieve greater environmental improvements for a given total budget.