Development of a habitat preference curve for the mayfly Baetis alpinus (Pictet 1843)

Habitat modelling provides a quantitative tool to predict scenarios in order to implement conservation measures and is therefore recognised as an effective method for managing running waters. Combining abiotic characteristics (e.g. substrate) and the results of hydraulic models (most commonly water depth and depth-averaged velocity), habitat models can be applied. Different models are available (e.g. CASiMiR, PHABSIM), all of which require preference (or suitability) curves for the species of interest. Choosing a species for habitat modelling requires sound knowledge of its ecology and distribution. The mayfly Baetis alpinus is a widespread and abundant alpine species and therefore a useful indicator species in the context of habitat modelling. Based on abiotic factors and abundance of the species, preference curves were established using polynomial regression. We present the sampling design and data processing for the establishment of a preference curve for the mayfly Baetis alpinus, including a review of its ecology. The application in habitat modelling is exemplified and discussed. Especially for high alpine environments, where fish are absent, the use of macroinvertebrates in habitat modelling enables to make comparable analyses of different flow rates.

Assessment of the transferability of biological habitat models for Atlantic salmon parr (Salmo salar)

We assessed the transferability of the habitat suitability index (HSI) and the habitat probabilistic index (HPI) between two rivers. Transferability was measured by the ability of HSI and HPI models developed in the Sainte-Marguerite River to predict the distribution of Atlantic salmon parr (Salmo salar) in the Escoumins River. HSI and HPI were based on the pattern of utilization by fish of water depth, current velocity, and substrate size. HSI was developed using the preference curve approach, and HPI was developed using a multiple logistic regression. Predicted values of HSI and HPI in Escoumins River ranged from 0 (poor habitat) to 1 (excellent habitat). Fish density in habitat patches assigned different HSI or HPI values ranged from 0 to 1 fish·100 m–2. Only HPI adequately predicted local variations in parr density (r2 = 0.84) in habitat patches of Escoumins River. Our results suggest that HSI is less transferable between rivers than HPI. Differences in substrate size between the two rivers is suspected to impede the transferability of the HSI model. We also argue that the mathematical structure of HPI provides a larger degree of flexibility that facilitates its transferability and its potential generalization.

Larval and pupal microhabitat selection by Simulium truncatum Lundström, S. rostratum Lundström, and S. verecundum AA (Diptera: Simuliidae)

Larval and pupal microhabitat selection by the cytospecies Simulium truncatum Lundström, S. rostratum Lundström, and S. verecundum AA was investigated. Last-instar larvae of S. truncatum and S. rostratum selected different microhabitats as shown by their response to velocity, depth, and outlets. Optimal stream velocity for larval S. truncatum and S. rostratum was estimated as 0.36 and 0.69–0.73 m/s, respectively. The microdistribution of S. truncatum showed a parabolic response to outflows with peak abundance occurring between 10.5 and 16.0 m from outlets. The distance-preference curve for S. rostratum was the complete inverse of that for S. truncatum, with maximum abundance of S. rostratum occurring immediately below and 20 m removed from the outlet. Abundance of larval S. truncatum decreased exponentially with depth (0.03–0.34 m), whereas the microdistribution of S. rostratum and a mixed 5. rostratum/S. verecundum AA population was not influenced by water depth (0.03–0.19 m). The microdistribution of pupae was similar to that of last-instar larvae for both S. truncatum and S. rostratum. Although larval microdistribution was influenced by velocity (S. truncatum, S. rostratum) and depth (S. truncatum), it was not possible to explain these patterns in relation to larval size.