The timing of adult sockeye salmon migration into fresh water: adaptations by populations to prevailing thermal regimes

Abstract

Anadromous fishes migrate to sea, apparently to take advantage of growing conditions, and return to fresh water to spawn. Despite favorable growing conditions at sea in summer, some populations leave the ocean in spring, many months prior to spawning. We hypothesized that this premature migration is a consequence of the fish having to avoid stressful summer temperatures in order to access certain suitable areas for spawning in the fall. We tested this idea in sockeye salmon, Oncorhynchus nerka, by compiling data on the timing of migration and spawning and the freshwater temperature regime along the migration route in populations throughout the species' North American range. The timing of migration varied among populations and was primarily related to temperature regime during migration and the timing of spawning. When temperatures were moderate (<19°C), sockeye salmon tended to migrate to the vicinity of the spawning grounds about 1 month prior to spawning, regardless of the length of the freshwater migration. However, populations on whose migration route the average temperature exceeded 19°C displayed two basic patterns. Some populations entered fresh water prior to the warmest period, months before spawning, whereas others migrated after the period of highest temperatures had occurred.

Effects of climatic variability on the thermal properties of Lake Washington

“…Lake Washington's sockeye salmon population is consistent with these patterns, and an early migration (33 d difference between the migration date and the date of peak average temperature; see Table 2 of Hodgson and Quinn 2002) before spawning helps to avoid the higher surface temperatures (20-22ЊC) that will be encountered during summer stratification. However, given the warming trends noted for Lake Washington in this study, longer spawning migration delays are likely to be triggered, with adverse repercussions for fish reproductive potential, especially egg size and fecundity (Hodgson and Quinn 2002). In addition, the warming trends in Lake Washington were associated with an observed proliferation of warm-water fishes (e.g., small-mouth bass) and the increased predation rates of warm-water piscivores, especially during springtime, when salmon smolts migrate out through the Lake Union/ship canal system (Stock et al unpubl.…”

A collective navigation hypothesis for homeward migration in anadromous salmonids

“…Moreover, genetic evidence indicates that Pacific salmon populations sponta neously sort by stock in space and time as they near shore (Dann et al 2013). Second, popula tions within watersheds often differ in the timing of their return to freshwater, which largely reflects differences in thermal regimes on the spawning grounds (Hodgson and Quinn 2002;Doctor et al 2010;Eliason et al 2011). These differences in when individuals begin their upstream migrations may act as a sorting mechanism as population specific run timing likely increases the probability of an individual finding a member of its group.…”

Interrelationships between feeding, food deprivation and swimming performance in juvenile grass carp

“…As would be expected, swimming efficiency in creased after digestion was complete and decreased with extended food deprivation. Swimming efficiency is particularly important for grass carp, since many fish species eat little or nothing during migration (Larsen 1980, Hodgson & Quinn 2002.…”