Abstract:
During spring, brook sticklebacks moved from deep, cold water in the main channel of the Roseau River into shallow, warm water in meltwater ponds and ditches, where they reproduced. Prior to reproduction, adults preferred the warmest available water, but avoided temperatures above 19-22* C. Post-reproductive adults were found in water above 22* C. Pre-reproductive adults moved upstream in current, although movement was influenced by water velocity, temperature and light intensity. Adults were found in deeper and colder water than young after parental behavior had ceased. The selected temperatures of acclimatized and acclimated brook sticklebacks were determined in the laboratory in a horizontal temperature gradient. Selected temperatures were influenced by reproductive phase, age, thermal history and season. Pre-reproductive adults selected a narrower range of temperatures than post-reproductive adults. Young selected higher temperatures than adults in early summer, but there was little difference in August. In addition young were more resistant to sudden fluctuations of water temperature than adults during early summer. Observations on the movements of both pre-reproductive adults and young in an experimental stream under varying conditions showed that upstream movement was greater in light than in darkness and was enhanced over a particular range of temperatures, which was higher for young than adults and was similar to the ranges selected in the laboratory gradient. Thus, water temperature and current appeared to influence the distribution and movements of brook sticklebacks.
