Seasonal Migration Patterns of Sub-Adult Striped Bass and Some Factors That May Trigger Movement Through the San Francisco Estuary

It is widely speculated that sub-adult (immature) striped bass in the Delta and San Francisco Estuary have the greatest predatory impact on delta smelt and juvenile salmonids although their population continues to decline while other predator fishes such as the Centrarchids increase.

 Although natural, anthropogenic, and predatory factors are thought to dictate sub-adult striped bass movement, current monitoring programs do not effectively measure distribution or migration, or its timing. We tagged and released 100 sub-adult striped bass during the summer of 2010 to observe their migration for 18 months via an array of more than 330 acoustic monitors placed throughout the Sacramento-San Joaquin watersheds, San Francisco Bay, and Pacific Ocean. Initial analyses indicate a summer-fall migration pattern into San Francisco Bay from the Sacramento and San Joaquin rivers, and Delta. Of the variables analyzed to date, migration into estuarine habitats appears to be driven by decreases in water temperature and turbidity. Evidence is emerging that subpopulations or cohorts may migrate long distances in unison. Clear understanding of which variables influence movement timing and migration of sub-adult striped bass may aid in the management of listed species such as the delta smelt and juvenile salmonids.