|Abstract or Summary
- Oregon's commercial fishery for albacore tuna (Thunnus alalunga)
is large, valuable, and variable. Little is known, however, about the
oceanographic factors which determine abundance and distribution of
Primarily using logbook data contributed by fishermen, this study
compares albacore catches with selected ocean conditions. The study
is limited to troll-caught fish taken during the summer of 1969 off the
Pacific Northwest. The location and success of commercial albacore
catches were analyzed with respect to the sea-surface temperature
field. Also examined was the relationship between fish catches and
sea-surface temperature, mixed-layer depth, and water color.
The 1969 albacore season off the Pacific Northwest lasted for 67
days, from 12 July to 16 September. Nearly 30 million pounds of
albacore, worth $6.7 million, were landed in Oregon ports, making
1969 the second best season in history.
The first commercial quantities of albacore were caught about
135 n mi west of Coos Bay. During the rest of July the fish moved
north somewhat but stayed well offshore. During August the fishery
spread out considerably, moving as far north as Vancouver Island.
In September fishing activity shifted south and inshore.
Off the Pacific Northwest no albacore were taken from waters
cooler than 54F(12.2C) or warmer than 66F(18.9C). Most fish were
taken from the sea-surface temperature range of 59. 5-63.5F(15.3-17.5C). July fish favored 61.5-63.5F(16.4-17.5C) water. By contrast,
August fish favored 59.5-63.5F(15.3-17.5C) water while
September fish favored 59.5-61.5F(15.3-16.4C) water. Catch-per-unit-
effort data did not indicate as marked a decline in availability at
cooler temperatures as did gross catch.
Mixed-layer depths associated with favorable albacore catches,
56-135 ft(17.1-41.1 m), were somewhat deeper than those determined
by previous investigations. Water-color results showed that most
albacore were caught in blue oceanic water.
Other factors associated with good fishing included favorable wind
and sea conditions, areas with considerable temperature structure,
plentiful food supply, presence of "tuna birds", and stable, moderately
developed upwelling situation.