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Special Studies Section - Predatory Fish Migratory Behavior

Riverine Res

low salinity zone res

click on thumbnails for larger images

Bay 1 res


Movement patterns differed seasonally between acoustically tagged sub-adult striped bass. Statistical and Visualization analyses showed three distinct movement patterns segregated defined by salinity: Riverine (<0.50‰), Low Salinity Zone (LSZ) (0.51-10.0 ‰), and Bay residence (10.1-30 ‰).

Riverine Residents remained within freshwater habitat across all seasons. LSZ Residents (Estuarine) exhibited movement primarily within mesohaline habitat, seldom visiting freshwater or marine habitats. The Bay residents moved within polyhaline and euhaline habitats across all seasons. This can be observed in the above maps entitled Riverine Resident, Bay Resident_1, and LSZ.

Three notable migrations occurred. In late spring 2011, an upstream migration was observed in the Riverine Residents. Some Bay and LSZ fish moved into the Sacramento (Colusa County) and Feather rivers (Sutter County) and Coyote Creek (San Clara County). This may indicate that some male fish matured and engaged in their first spawning run. In fall, an upstream foray was undertaken by a few Bay and LSZ Residents into freshwater habitat averaging 14 days, with fish returning to their departure location. This can be observed in the maps below entitled Bay Resident_2, South Bay Migrant, and Fall Migrant.

Our findings are consistent with recent otolith microchemistry studies in the SFEW. As described on the Atlantic Coast, Riverine Residents may be dominated by immature male fish where the Bay Residents may be composed of females. The movement patterns of sub-adult striped bass could have important consequences to the management of the recreational fishery, ESA-listed species recovery plans, and future restoration planning. We recommend that future management consider the effects of striped bass bimaturation (males mature at age 2 years; females between ages 4-6 years), its impacts on movement patterns, and predation.