Hierarchical analysis of habitat use by 0+ juvenile fish in Hungarian/Slovak flood plain of the Danube River

Synopsis To address the lack of information on the distribution and habitat use of 0+ juvenile fishes in the Hungarian/Slovak flood plain of the middle Danube River, we undertook the first cross-border ichthyological investigation, examining three levels of ecological perception (hydrosystem, macrohabitat, microhabitat) during August 1992 using ‘Point Abundance Sampling’ by electrofishing. Being that the Gabćófcovo hydroscheme was about to begin diverting most of the river's discharge away from the flood plain during the winter of 1992, the present investigation represented the last chance to record the distribution and microhabitat use of 0+ fishes within the flood plain. At each sampling point, numerous environmental variables were measured quantitatively, or as percentages. At the hydrosystem level, 25 species of 0+ fishes were captured in the 1170 point samples collected from 52 sites (27 in Hungary, 25 in Slovakia), ranging from 10 to over 200 mm standard length (i.e. pikeEsox lucius). No significant differences were found between the Hungarian and Slovak specimens with respect to standard length (ANOVA, p> 0.31), nor in the relative densities (ind.m⁻²) of 0+ fish (Student's t-test: df 24, t = 0.601, p = 0.553). A typology of macrohabitats using principal components analysis of the sites X species data matrix in absence/presence revealed three groupings of sites: (1) lotic channels, weirs and wing-dams; (2) partially-abandoned channels; (3) abandoned channels; the results corroborated our assumption that weirs of the anabranch systems represent a quasi-lotic refuge for rheophilous 0+ fishes of the flood plain during late summer. At the microhabitat level, an empirical model of microhabitat use was generated using canonical correspondence analysis and association analysis (based on chi-square probabilities). Water velocity was the most influential variable, with the O+ juveniles ordinated along the first canonical axis according to their increasing rheophily. The second most influential microhabitat variable was water transparency, followed by the percentage abundance of macrophytes and substrate composition.     

An outcome-based model for predicting recovery pathways in restored ecosystems: The Recovery Cascade Model

Restoration is increasingly the focus of ecosystem management. Few conceptual models exist for predicting the consequences of restoration, especially those that predict the stages of recovery following restoration. Existing models focus either on defining endpoints for recovery or on defining ecosystem processes, but often do not identify barriers to recovery or potential negative effects of restoration. We describe a conceptual model that identifies the outcomes of the recovery pathways following flow restoration in rivers: the Recovery Cascade Model. The model identifies six general aspects of recovery following restoration: physical ecosystem change; creation of, or improvement in habitat condition; reconnection of the restored area to adjacent ecosystems; recolonization of the restored area; resumption of ecological processes; re-establishment of biotic interactions and reproduction by colonists in the restored area. These aspects may occur in sequence, such that recovery is blocked by a single barrier. The model accommodates feedback loops and includes strong connections between physical processes and ecosystem processes, but also identifies factors that are important in achieving endpoints such as potential barriers to further recovery. Identification of barriers to recovery enables improved planning to maximise the positive effects of restoration. By focussing on outcomes, the model provides a planning tool for managers that can be adapted for different ecosystems and restoration methods and which can be used to identify the amenities that an ecosystem will deliver at different stages of recovery. Ecosystem recovery is as much about overcoming barriers as it is about restorative actions.     

An advanced Index of Biotic Integrity for use in tropical shallow lowland streams in Costa Rica: Fish assemblages as indicators of stream ecosystem health

This paper presents an advanced version of the Index of Biotic Integrity (IBI), a multimetric index to indicate ecosystem health. The multimetric index has been adapted in such a way that it not only indicates overall condition but also specific causes of environmental disturbance. The newly developed index (a) uses data of tolerant as well as intolerant species in a single metric to indicate environmental disturbance, (b) does not require knowledge about species from the literature, and (c) can be applied to artificial landscapes.The metrics proposed here consist of indicator species assemblages that are selected directly for their relationship with an environmental component or specific type of environmental degradation. Thus, each metric indicates a type of environmental concern, which enables conservation practices to be targeted more effectively. Species assemblages for each single metric consist of a combination of species that can be negatively and positively related to environmental disturbances, providing a better indication of stream ecosystem health.The area studied was assumed to be too diverse for one single index. Canonical Indirect-Gradient Principal Component Analysis indicated that the optimal division of subindices based on stream typology was for streams with drainage basin sizes <10 km² and >10 km². Pearson Product-Moment Correlations were used to identify relationships between anthropogenic disturbances and the composition and abundance of fish species at impacted as well as undisturbed sites. This index proved to be useful for indicating overall stream ecosystem health as well as local onsite environmental disturbances or the environmental components of greatest concern. This index does require extensive information about measured levels of anthropogenic disturbances with the accompanying composition and abundance of fish species.     

A comparison of modeling techniques to predict juvenile 0+ fish species occurrences in a large river system

Even if European river management and restoration are largely supported by the use of reliable tools, these tools are most often “generalist” and provide only initial leads of alteration sources. Acknowledging that young-of-the-year (YOY) fish assemblages are highly dependent on riverine habitat conditions, the development of a YOY-based tool might be very useful or even essential in the design and implementation of conservation or restoration plan of large rivers, in measuring more straight-forward the losses and gains of hydro-ecological functionalities. In the past 20 years, new modeling techniques have emerged from a growing sophistication of statistical model applied to ecology. “Machine learning methods” (ML) are now recognized as holding great promise for the advancement of understanding and prediction of ecological phenomena. The aim of this work was to select the appropriate statistical technique to model YOY assemblages according to different meso-scale habitat variables that are meaningful to planners. To do this, two “Machine Learning” methods, Classification and Regression Trees (CART) and Boosted Regression Trees (BRT), were compared to Generalized Linear Models (GLM). We modeled the occurrence of 9 species from the Seine River basin (France) in order to compare models abilities to accurately predict the presence and absence of each species. BRT appeared to be the best technique for modeling 0+ fish occurrences in our dataset.