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PART II -PROPOSED CRITICAL HABITAT DESIGNATION Determination of Critical Habitat General--In determining azeas for designation as critical habitat for a species, the Service considers those physical and biological features (i.e., constituent elements) that are essential for its conservation. Such physical and biological features are stated in 50 CFR 424.12. and include, but are not limited to, the following items: (1) Space for individual and population growth, and for normal behavior; (2) Food, water, air, light, minerals, or other nutritional or physiological requirements; (3) Cover or shelter; (4) Sites for breeding, reproduction, rearing of offspring, germination, or seed dispersal; and generally; (5) Habitats that are protected from disturbance or are representative of the historical geographical and ecological distributions of a species. In addition, the Act stipulates that the azeas containing these elements may require special management considerations or protection. In considering the biological basis for determining critical habitat, the Service focused on the primary physical and biological elements essential to the conservation of each species. This relationship was a prime consideration in the designation of critical habitat. The Service is required to list the known primary constituent elements together with a description of any critical habitat that is designated. The primary constituent elements determined necessary for survival and recovery of the Virgin River listed fishes include, but aze not limited to: Water--A quantity of water of sufficient quality (i.e., temperature, dissolved oxygen, contaminants, nutrients, turbidity, etc.) delivered to a specific location in accordance with a hydrologic regime that is identified for the particular life stage for each species. Physical Habitat--Areas of the Virgin River system that are inhabited or potentially habitable by fish for use in spawning, nursing, feeding and rearing, or corridors between such areas. In addition to river channels, these areas also include side channels, secondary channels, backwaters, springs, and other areas which provide spawning, nursery, feeding or rearing habitats, or access to these habitats. Biological Environment--Food supply, predation, and competition are important elements of the biological environment and are considered components of this constituent element. Food supply is a function of nutrient supply, productivity, and availability to each life 6