Ocean Temperatures and Their Relation to Albacore Tuna (Thunnus germo) Distribution in Waters off the Coast of Oregon, Washington and British Columbia

Abstract

Commercial albacore fishing offshore from Oregon, Washington and British Columbia, occurs during summer months when offshore surface water temperatures exceed 58°F (14.4 °C). Fishermen have established 58°F (14.4 °C) surface temperature as an indicator of "tuna water", and this rule-of-thumb relationship for surface water temperatures and albacore has generally been substantiated by total catch versus temperature records made during albacore investigations. Catch-per-hour data are also in accord with this general thesis. Catch-per-unit-effort data, however, do not indicate as marked a decline in availability at temperatures between 54 and 58°F (12.2–14.4 °C) as might be interpreted from qualitative observations. With the exception of one albacore caught by a gillnet in 1956, all albacore have been taken in Bureau investigations where surface temperatures exceeded 54°F (12.2 °C) and highest catch rates were obtained between 58 and 61°F (14.4–16.1 °C). As the thermocline depth averages about 60 feet (18.3 m) in the summer months offshore from the Pacific Northwest states and temperatures are all well below 50°F (10 °C) at the bottom of the thermocline, albacore probably inhabit only the overlying (mixed layer) lens of warm oceanic water. Concentrations of albacore appear to occur along the interface of the warm oceanic waters and the cooler waters adjacent to the coast.