When Is Habitat Limiting for Striped Bass? Three Decades of Testing the Temperature-Oxygen Squeeze Hypothesis
Charles C. Coutant
Abstract.—Striped bass Morone saxatilis, originally a coastal and estuarine species, has been introduced in reservoirs in the southeastern and western United States. Although such stocking established many successful fisheries, there were troublesome die-offs of adult striped bass (3–9 kg, generally >5 kg) in some waters, usually in late summer. In contrast, juveniles and small adults thrived. In response to these patterns, my students and I conducted several years of telemetry studies of adult striped bass, primarily in Cherokee and Watts Bar reservoirs, Tennessee, and laboratory studies of juvenile temperature selection. In 1985, I published the “temperature–oxygen squeeze” hypothesis to explain mortalities of large fish on the basis of limited availability of cool (<25°C), oxygenated (>2 mg/L) water in summer while juveniles successfully occupied a warmer thermal niche (>25°C). We now have more than 20 years of research and management since 1985, primarily across the Southeast, in which the published hypothesis has, explicitly or not, been tested, generally confirmed, and applied to management. This retrospective paper reviews the studies our team conducted to develop and test the hypothesis and about 20 years of relevant studies by others that have added important nuances, addressed lingering issues, and turned a controversial idea into generally accepted understanding and management practice. Nonetheless, issues remain for understanding the effects of poor summer habitat on striped bass, such as why some studies show striped bass occupying warmer temperatures without mortalities and the role of prey availability in survival of fish obliged to occupy warm water. Other papers in this volume augment and extend the saga of progressively developing knowledge that this paper recalls of striped bass habitat requirements, thermal niche segregation by size (or age), and management constraints and opportunities.