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and Yarzhombek (1975) concluded that 4.0 to 4.5 mg/1 can be considered the critical concentration of dissolved oxygen for young striped bass at 22° C (71.6° F). Larval (dissolved oxygen, V2~. Egg and larval requirements for dissolved oxygen are assumed to be the same for both lacustrine and riverine habitats. Special Considerations Riverine habitat having a high HSI may not produce striped bass larvae, and a high HSI for lacustrine habitat does not necessarily indicate a high standing crop of striped bass. Numerous factors, including hatching success and survival of fry, spillway escapement, amount and availability of suitable forage, size and number of predators that feed on striped bass, stocking practices, and fishing pressure, can influence year-class size and abundance. Forage species eaten by juvenile and adult striped bass also are utilized by other prey species. The abundance of forage species is influenced by physico- chemical variables, making their availability to striped bass uncertain. High temperatures in the epilimnion and low dissolved oxygen concentra- tions in deep, cooler areas of a reservoir may bring about an environmental "squeeze" during warmer months, causing adult striped bass to seek refuge in relatively small, spring-fed coves or in tailwater areas (Coutant 1978; Schaich 1979; Waddle 1979; Cheek 1982; Cheek et al. 1985; Matthews 1985; Moss 1985). The "squeeze" may temporarily greatly reduce the volume and area of suitable habitat available to adults. While "squeezed" in the refuge, adults are highly vulnerable to parasites and diseases and to harvest by anglers. In- adequate food may result from increased competition for available forage, and fish may quit feeding and die due to the undesirable environmental conditions. Thermal stress and/or low levels of dissolved oxygen have been reported to result in mortality of adults in freshwater reservoirs (Axon and Whitehurst 1985) but summer mortality is by no means universal (Mathews 1985; Mathews et al. 1985). Wooley and Crateau (1983) found that striped bass weighing 4.5 to 6.7 kg (9.9 to 14.8 lb), captured in coolwater refuges during the summer, showed a significant weight loss since the previous spring. However, adults weighing less than 4.5 kg (9.9 lb) had gained weight throughout the summer. Adult and subadult striped bass collected from summer (June) refuges had lower condition factors than those collected during April-May (Moss 1985). HABITAT SUITABILITY INDEX MODELS Model Applicability These models are not applicable to habitat overburdened with toxic chemicals or heated effluents or to rapidly fluctuating conditions, such as sudden changes in water temperature or river discharge during the spawning season. If contaminants are suspected to affect habitat suitability, guide- lines on quality criteria for water are available from State water quality control agencies, the U.S. Environmental Protection Agency (1976), and Thurston et al. (1979). 18