 Striped Bass (Morone saxatilis)
 Distribution of striped bass in San
Francisco Bay
Striped bass are a non-native fish introduced from the East Coast more
than a century ago. The population exploded shortly after the introduction and major commercial
and recreational fisheries developed. Due to public perception about impacts on the valuable
recreational fishery, commercial fishing for striped bass was outlawed by the legislature in 1935.
Striped bass have two major spawning areas: the Sacramento River between Sacramento and
Colusa and the western Delta in the San Joaquin River between Antioch and Venice Island.
Most spawning in the Delta occurs from April through May. Striped bass spawn in essentially
fresh water; therefore, the salinity regime in the western Delta is important. Salinities on the San
Joaquin side of the Delta are lowest in the vicinity of the mouth of the Mokelumne River where fresh
water from the Mokelumne and Sacramento systems dilutes water flowing from the upper San Joaquin River
which has accumulated salts from agriculture drains in the San Joaquin Valley. Farther west, the river
becomes more saline due to the intrusion of ocean water.
Adult striped bass abundance has decreased in stages, from 1.7 million in the early 1970s
to about 1 million in the late 1970s and 1980s, then to about 625,000 in 1992.
DFG has found that this trend can be largely explained by the detrimental effect on young
bass production of increasing water exports and decreasing freshwater flow.
Distribution of adult bass, based on tag recaptures by anglers, has changed substantially.
Bass no longer make extensive use of San Francisco Bay and instead spend a greater part of
the year in the Delta and other upstream areas. Summer use of nearby ocean waters may
have increased recently, also. Total mortality of adult striped bass has increased since
the element began due to an increase in natural mortality. Angling mortality has declined
somewhat.
Variations in adult abundance are well-explained by the combination of the 38 mm
young-of-the-year index and losses to water export pumping after the 38 mm index is set.
The 38 mm index and subsequent export losses are both dependent on export rates and outflow,
so that adult abundance is affected by exports and outflow throughout the year.
Annual abundance indices for striped bass are calculated for
various stages of there development
data by the Adult Striped Bass Population Program, and the
Midwater Trawl Program.
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