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<br /> <br />, <br /> <br />High nutrients <br /> <br />THE INSTREAM FLOW INCREMENTAL METHOLDOLOGY 17 <br /> <br />Sandy bed <br /> <br />Low D.O. <br />Phytoplankton food base <br /> <br />Fig. 3.1. Longitudinal succession schematic. Shading denotes approximate gradient from headwaters to intermediate <br />stream to mature river. <br /> <br />made particular note of a fish's adaptations for <br />inhabiting areas of high velocity, such as stream- <br />lined body shape, expansive fins, and specialized <br />mouth. Similar observations of the distributions of <br />aquatic invertebrate species were documented by <br />Sprules (1947). These investigators concluded that <br />bottom type (substrate material) and velocity were <br />the most significant determinants of invertebrate <br />production and diversity in streams. <br />During the 1960's and 1970's, researchers <br />learned that the distributions of fish and inverte- <br />brates were not random, even within the same <br />habitat types, and began to investigate determi- <br />nants of microhabitat selection (see Fig. 3.2). The <br />three most commonly cited mechanisms involved <br />reproductive success, energetic advantage, and bi- <br />otic interactions (competition and predation). <br /> <br />Reproductive Success <br /> <br />Salmonid redds are typically located in areas <br />with clean gravel, with enough velocity to prevent <br /> <br /> <br />:.;.~.."'_.'"..''''.''' "J' <br />...-. _....._ ."M'"'' <br />-'''-''';,,_!' ~ <br />,.. <br /> <br />Side view <br /> <br />~ Fast water <br />ITIill Slower water <br />. Riverbed <br /> <br />Fig. 3.2. An example of microhabitat specificity. <br />