– The required freshwater habitats of juvenile Atlantic salmon (Salmo salar) are, in general, well known, but vary in quality, related to interacting effects of several variables, which may depend on different parts of a river system. Examples are given of ranges of densities and growth that can be found at various sites in eastern Canada, illustrating the biological and physico-chemical factors affecting production of juvenile salmon. Relative growth rates can indicate habitat quality and population densities. Salmon parr have negative effects on brook trout in riffle habitats. The effects of migrations within the river and of changes with stream succession on juvenile salmon production are illustrated with examples from a Newfoundland river. Migration of age-classes can be quantified from ‘self-thinning’ curves. Lakes have enhancing effects on downstream fluvial habitats, and, at least in Newfoundland, and probably in many boreal areas, the lacustrine proportion of the basin can be used as an index for deriving estimates of required spawning escapement. The factors described should be taken into account for more refined estimates of river production and management of the salmon resource.

The effects of fluvial processes and habitat heterogeneity on distribution, growth and densities of juvenile Atlantic salmon (Salmo salar L.), with consequences on abundance of the adult fish

https://www.bio.ulaval.ca/labdodson/Papers%20Julian/Hedger_EcolModel2006.pdf

Improving models of juvenile Atlantic salmon habitat use through high resolution remote sensing

Knowledge of the factors that drive species distributions provides a fundamental baseline for several areas of research including biogeography, phylogeography and biodiversity conservation. Data from 148 minimally disturbed sites across a large drainage system in the Cape Floristic Region of South Africa were used to test the hypothesis that stream fishes have similar responses to environmental determinants of species distribution. Two complementary statistical approaches, boosted regression trees and hierarchical partitioning, were used to model the responses of four fish species to 11 environmental predictors, and to quantify the independent explanatory power of each predictor. Elevation, slope, stream size, depth and water temperature were identified by both approaches as the most important causal factors for the spatial distribution of the fishes. However, the species showed marked differences in their responses to these environmental variables. Elevation and slope were of primary importance for the laterally compressed Sandelia spp. which had an upstream boundary below 430 m above sea level. The fusiform shaped Pseudobarbus ‘Breede’ was strongly influenced by stream width and water temperature. The small anguilliform shaped Galaxias ‘nebula’ was more sensitive to stream size and depth, and also penetrated into reaches at higher elevation than Sandelia spp. and Pseudobarbus ‘Breede’. The hypothesis that stream fishes have a common response to environmental descriptors is rejected. The contrasting habitat associations of stream fishes considered in this study could be a reflection of their morphological divergence which may allow them to exploit specific habitats that differ in their environmental stressors. Findings of this study encourage wider application of complementary methods in ecological studies, as they provide more confidence and deeper insights into the variables that should be managed to achieve desired conservation outcomes.

/pdf/contrasting-habitat-associations-of-imperilled-endemic-3e32ftpynq.pdf

Contrasting habitat associations of imperilled endemic stream fishes from a global biodiversity hot spot

The strength of a population resides in the resilience of its individuals and is closely related to the stability of its habitat. Stream macro-invertebrates are sensitive to environmental changes concerning habitat stability; thus, they require shelter to prevent drift during severe floods. We propose a novel approach to estimate the impact of flash floods upon the substrate, by introducing a variable named ‘flash-flood potential’ (FFP), which accounts for the site slope and the average slope of the upstream catchment. We investigate the impact of this variable on the distribution of two important crayfish species, Austropotamobius torrentium and Astacus astacus, in Romania. We focus on the connection between crayfish abundance and FFP, and also on the role of the individuals' body size in shelter allocation, considering shelter stability as a key factor in coping with the disturbances. The results show that both species are sensitive to influence of the FFP, A. torrentium apparently having a slight advantage. The size of populations visibly decreased with the increase of FFP, those in the upper range having few individuals, which were mainly found in very stable shelters. Individual analyses reveal that the most durable shelters were generally occupied by the largest crayfish. We hypothesize that the competition for shelter is an indirect driver for preventing the drift of crayfish populations. Copyright © 2016 John Wiley & Sons, Ltd.

Flash‐flood potential: a proxy for crayfish habitat stability

The use of fertilisers in agrieultural and forestry aetivities and the spread of urbanisation aggravate enriehment and pollution of waterways (HYNES 1970, 1975). It is well reeognised that water ehemistry affeets salmonid produetion (e.g. HuET 1964, HYNES 1970, EGGLISHAW & SHACKLEY 1985), and that although pollution results in negative effeets, enriehment may result in inereased produetion of salmonids (e.g. HuNTSMAN 1948, MILLS 1969, RAsMUSSEN 1986, BERGHEIM & HESTHAGEN 1990). Jneidental enriehment has eonrributed to extraordinarily high biomasses of salmonids in the rivers of St. John's, the eapital eity of Newfoundland and Labrador, Canada (GIBSON & HAEORICH 1988). Brown trout, Salmo trutta L., were inrrodueed inro the eity rivers about 100 years ago (ANDREWS 1965) and presenrly are eommon throughout all the systems. The indigenous brook trout, or brook ehar, Salvelínus Jontínalís (Mitehill), is still present, although most eommon in the headwaters of these rivers, possibly related to these areas remaining undisrurbed from ehannelisation, and retaining the original riparian vegetation, with a more disturbed habitat and eompetitive interaetions favouring the brown trout downstream. Due to its glaeial history, the fish fauna of the island ofNewfoundland is depauperate generally (Scorr & CROSSMAN 1964), and only rwo other fish speeies oeeur in the eity rivers of St. John's: three-spine stieklebaek, Gasterosteus aculeatus L., an d the Ameriean eel, Anguilla rostrata (Lesueur). The present study elaborates on previous work, by sampling salmonids down the length of a stream in the eity, through a range of enriehmenr, and by relating the growth rates to the food base.

The response of salmonids and aquatic invertebrates to urban influenced enrichment in a Newfoundland river, Canada

Three methods were used to estimate coarseness of substrate within experimental stations in four Newfoundland rivers: (1) a categorical rating was derived by estimating proportions of types of all the substrate within an area; (2) a similar type of rating was derived, but from substrate types within 30 cm sections delineated on a lead rope stretched across the station; and (3) an index of coarseness of the substrate was measured from a depth sampler constructed of 11 sliding rods supported within a 1 m long frame. The rod, or depth, sampler was considered to provide the least subjective method and could therefore provide an index to validate the other methods. Compared with the standard deviations of depths for the rod sampler, the categorical ratings from the general estimate had an rs= 0.85, and the 30 cm sampler an rs= 0.86. It was deduced that the two methods of visually estimating substrate types in shallow clear rivers are reasonably adequate methods for describing coarseness, but that the depth sampler would be the more precise under certain conditions.

R. R. Whalen

Papers

A comparison of three methods for estimating substrate coarseness in rivers