The Role of Mysid Shrimp in the Sacramento-San Joaquin Estuary and Factors Affecting Their Abundance and Distribution
James J. Orsi, California Department of Fish and Game
Arthur C. Knutson, Jr., California Department of Fish and Game

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ABSTRACT:

Six species of mysid shrimp are present in the Sacramento-San Joaquin Estuary, but only one of them, Neomysis mercedis , is abundant here. It is an important fish food in Suisun Bay and the Delta, especially for young-of-the-year striped bass. N. mercedis feeds on phytoplankton, detritus, and zooplankton. Its distribution is apparently determined by estuarine circulation acting on its vertical migration pattern. These factors concentrate it in the zone where fresh and salt water initially mix. Light intensity greater than 10 ^-5 lux on the bottom and net flow velocity <0.12 m·s^-1 apparently limit its upstream spread. In the San Joaquin River low populations are associated with low dissolved oxygen concentrations in combination with high temperatures. Fecundity appears to be a function of female length, temperature, and food supply (phytoplankton). Seasonal fluctuations in reproduction are usually paralleled by population fluctuations. Population differences between years appear to be a function of food supply and habitat size.

 

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