Charrs, glaciations and seasonal ice

Synopsis

Although the paleontological evidence is sketchy, the genus Salvelinus appears to have arisen some 5–10 million years (My) ago. During most of the last 0.6 My, and for a long period before that, the charrs existed in periglacial environments just beyond the fringes of great ice sheets. The charrs of eastern North America evolved and live in close and intimate association with ice in all its various natural forms. The aquatic environments in which they evolved were cold, unproductive, sediment laden, and often catastrophically unstable. Even during times like the current interglacial, seasonal ice conditions influence their environment. Ice can limit movement and confine fish during winter to groundwater fed refuge areas in rivers or to deep waters. In rivers, spawning grounds may be delimited by suitable groundwater upwellings needed to protect eggs and embryos from ice. In lakes, ice thickness and, often, groundwater upwellings help define suitable spawning areas which often occur in ice molded glacial deposits. Not surprisingly, many of the traits displayed by eastern North American charrs can be recognized as beneficial in cold regions. Particularly valuable is their opportunistic, exploratory, and migratory behaviour which helps define their life history. These traits were presumably selected during life in periglacial areas and would have been useful for dispersal whenever ice sheets retracted. It is unlikely these traits will promote survival under present circumstances when human activity is rapidly modifying their environment. However, should modem technology enable the necessary information to be obtained and, with guidance, society responds appropriately, it is possible the charrs will persist into the future.