Movements of Brook Trout, Salvelinus fontinalis (Mitchill), Between and Within Fresh and Salt Water

Abstract

Major movements of trout into Ellerslie Brook, Prince Edward Island, were in April, June–July, and November; and out in May and October to early January. Some movements were preponderantly in one direction; others involved trout making simultaneous movements up- and downstream. Mean length of trout in movements was 16.8 cm., predominantly age II. Trout were short-lived and few survived to make repeated movements. About 50% of trout making return movements did so within a month. Percentage of Ellerslie-reared trout which ran to salt water varied from 12 to 35 over a 6-year period. There was inconclusive evidence of a heritable propensity to sea-running. After descending into the estuary, few trout left for open coastal waters. Short-distance movements resulted in population shifts in the brook in summer which were not detected in traps at mouth of stream.Movements of trout between fresh and salt water were very closely associated with rise and fall of the water level in the brook, but not with height of water. Movements in spring and early summer were into preferred temperature. Although marked changes in water level occurred, few trout moved in winter after becoming acclimated to a water temperature of 0 °C. or in summer when brook was at temperature of final preferenda. Continuance of movement for some time after 0 °C. was reached seemed related to slow rate of acclimation. Movements were both random and directed. For most movements trout appeared conditioned by temperature and stimulated by changing water levels. Trout moved largely at night. Other influencing factors were living space, maturation and spawning. Turbidity, salinity, tides, and handling were without apparent effects.