SEASONAL CURRENT HOLDING PERFORMANCE OF JUVENILE ATLANTIC SALMON IN RELATION TO TEMPERATURE AND SMOLTING

The ability of juvenile Atlantic salmon to hold station against a wate r current was tested in relation to season, environmental temperature, and developmental strategy. The finding that holding velocities, rela tive to body length, were similar in the faster growing, earlier smelt ing fish (upper modal group) and the fish remaining in freshwater for a further year (lower modal group) suggests that there was no differen ce in relative performance or habitat availability. Seasonal changes i n performance were generally related to water temperature, with the de crease in holding ability becoming more pronounced at low temperatures . The relative critical holding velocity of smelting fish was lower ov er the period of seaward migration than in previous months. However, w ithin this period, critical holding velocity increased with degree of silvering. The implications of these results for the ecology and life- history strategy of juvenile salmon are discussed.