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The descriptions and discussions below may seem obvious and insignificant, but they are in fact a key to understanding the Saskatchewan River and its inhabitants. Streams can range from cool, shaded, rapidly flowing waters in upstream, possibly mountainous areas, to the slow, meandering, and sunny conditions far downstream. Rivers are often muddy and slow moving, but rivers can sometimes be more like large streams than rivers.
If all the organisms living in the Saskatchewan River are to be found, it is important to know that many species are very restricted in their distribution and habitat requirements, and that certain habitat types are isolated and sometimes rare. Detailed knowledge of the river is necessary if you want to find what you are looking for in the river, and random sampling for ecological or pollution studies will collect only a small portion the the inhabitants of the river and will give distorted information on density, populations, and distribution. The stress on random sampling required by many protocols and textbook methods seem remarkably uninformed and simplistic regarding this point.
Unique Habitats found in the Saskatchewan River
While rivers in the lower reaches may consist mostly of muddy and sandy substrates, rivers such as the Saskatchewan have relatively little of this kind of habitat. The Saskatchewan River provides habitats for a great variety of specialists, ranging from inhabitants of sandbars to rapids and white water to muddy backwaters. Species from a wide range of taxonomic groups contribute to a very diverse and unique river invertebrate community in the Saskatchewan River System.
Again, a practical consideration is sampling methods- standard methods in textbooks and scientific publications often recommend, even require, the use of small, ineffective and inappropriate samplers, and the use of a random sampling design. This will almost certainly result in the failure to collect any but the most common species.
Major types of habitats and their significance are discussed below, along with some species that are dependent on these ecological conditions
Special habitats include submerged sandbars, which are large areas of clean, current swept, fine sand of uniform grain size, constantly shifting from the action of the current. Two of the species discussed under species accounts are restricted to submerged sand bars, namely Ametropus neavi and Pseudiron centralis. Each has unique morphological adaptations:
Pseudiron centralis is crab-like, and moves over the sand, backward, forward, and sideways, using the six anchoring points of long claws to plunge deeply into the sand, and thus give the organism complete control and stability as it moves over the current-swept sand, searching for prey with long mouthpart palps, which sweep the sand as it moves (Lehmkuhl, unpublished).
Ametropus neavi anchors 4 claws in the shape of the comers of a square, and here it sits while facing upstream, filtering food from the passing current with the fine hairs on the front legs, mouthparts, and special prostenal projections. It uses the front legs to examine and sort the particles collected, and then passes food material on to the mouth (Lehmkuhl, unpublished).
In many areas of the river there are extensive growths of willow near the shoreline or on sandbars. Roots from these willows radiate long distances, including under the river channel. As the current cuts deep into the substrate, these roots may be exposed, so that the river bottom is covered by mats or single strands of roots, which range from fibrous to pencil-size in diameter, and this provides a strong, stable, easily grasped substrate for some species. The species Lachlania saskatchewanensis, which has been regarded as rare and elusive to collect by many, is almost always associated with willow roots, where it can live in water a meter or more in depth, cling to roots, and filter food from the passing current (Lehmkuhl, unpublished).
Logs and Branches
Logs, branches, leaves, and other material fall into the river and are carried by the current, and are often deposited in backwaters. These undergo stages of decay, while at the same time serving as an anchor point for other floating material. Wood undergoes a complex succession of fragmentation and decay, involving a sequence of insect shredders, gougers, scrappers, and fragmenters, as well as a sequence of fungi and bacteria. One species treated in a status report (Macdunnoa nipawiniaLehmkuhl) is almost always associated with dead tree branches, which have been in the water long enough so that the bark is loosened, so that there is a space between the bark and the wood, but the bark still partially surrounds the original branch. These branches cannot be in muddy, stagnant conditions in backwaters, but must be washed to some degree by the passing current (Lehmkuhl, unpublished).
Depositional zones and backwaters
The irregular shoreline of the river causes many disruptions in the smooth flow of the current, and there are all degrees of backwaters and depositonal areas, and in these areas, the complete range of current conditions and substrates can be found, ranging from a complete lack of current, to gentle current, to strong current, and a complete range of substrates, ranging from soft mud to clean gravel and stones. It is in these backwaters, during the falling water after floods, that large numbers of the rare species Analetris eximia have been collected. The true habitat of this species is not known, since it is a vigorous, fish-like swimmer, which easily evades small collecting nets. After violent flooding, displaced individuals accumulate as a result of the current in backwaters, and have sometimes been collected in large numbers.
Clean washed stones and rubble
Rivers have large areas of current-swept stones, gravel, and rubble, consisting of stones ranging from 1 cm to 15 or 20 cm in diameter. It is important that these not be actually embedded in mud, but rather they should be piled on one another in such a way that space exists under the stones, and this space under the stones is a retreat and living area for a large community of aquatic insects. In a natural river there will be a modest growth of epiphytes on the stone surfaces, a small amount of partially decomposed material will be carried to the stones by the current, and the base of a food chain will be provided by this plant growth and dead plant material; in the Saskatchewan river a herbivore community of several dozen species will feed on this material, and a small number of species but a large biomass of species of predatory insects will feed on the herbivores. All of these organisms will provide food for fish (e.g. Lehmkuhl 1981).