Albacore Migration

The North Pacific albacore stock, particularly the juvenile fish (2-5 year olds), typically conduct an expansive annual migration that begins in the spring and early summer in waters off Japan, continues throughout the late summer into inshore waters off the U.S. Pacific coast, and ends late in the year (late fall and winter) in the western Pacific Ocean. It is generally believed that oceanic conditions strongly influence both the timing and geographical extent of the albacore's migration in a given year. Migrating albacore concentrate along thermal discontinuities (oceanic fronts) associated with waters of the Transition Zone in the North Pacific Ocean. The vast majority of albacore are caught in waters with sea-surface temperatures (SSTs) that range from 15o to 19.5o C (59o -67o F). The migrating fish are typically bounded by these thermal gradients as they conduct their round-trip travel across the Pacific Ocean. Although the bulk of the migrating stock is typically observed within this SST range, telemetry studies have shown that this species will spend brief periods of time in much colder water (9.5o C).

Upwelling, where nutrient-rich waters from the ocean depths rise to the surface, is another important phenomenon associated with oceanic fronts and ultimately, an event that highly influences the distribution of the migrating albacore. It is likely that the albacore are attracted to upwelling fronts, given these areas are very productive and contain much forage for predatory fish. Although scientists are quite certain that oceanic fronts are critical phenomena when defining albacore distribution and thus, vulnerability to fisheries, they feel other oceanographic parameters also influence the migratory behavior of the stock, including salinity, ocean color and clarity, and vertical thermal/density structure. In general, catches from the commercial fisheries indicate the albacore are most abundant along the warm side of upwelling fronts in clear blue oceanic waters that are associated with salinity gradients between 33 and 35 parts per thousand and well-defined thermoclines (vertical stratification of the ocean due to density/temperature changes based on depth).

Recent research indicates that the albacore adjust their behavior to very different oceanic conditions when passing through at least four distinct physical regimes (geographical strata) of the North Pacific Ocean, i.e., determining what are the most influential environmental parameters depends on where in the ocean (spatial) and what time of year (temporal) the assessment is conducted.