 Crangon franciscorum
 Distribution of Crangon franciscorum in San
Francisco Bay
Crangon franciscorum (the California bay shrimp) is a euryhaline species that is the
dominant caridean shrimp in most Pacific coast estuaries and the most common species
in the Bay. It is distributed from southeastern Alaska to San Diego, California. In
the Bay C. franciscorum are usually distributed from South to Suisun and Honker bays,
but have been collected as far upstream as the San Joaquin River at Middle River.
Juveniles prefer shallow (<15'), low salinity waters and migrate to deeper, higher
salinity waters as they grow. C. franciscorum reaches the largest size of the shrimp
species common to the Bay; this study collected females to 87 mm total length (TL) and
males to 68 mm TL.
Ovigerous females are most abundant in the late winter and spring in South, Central,
and lower San Pablo bays, although in years with high freshwater outflow, they are
concentrated in the nearshore ocean area. Mature males apparently migrate with
ovigerous C. franciscorum to higher salinity waters. After fertilization, it takes
10 to 12 weeks for larvae to hatch in the spring. Larvae developed to post-larvae in
14 to 20 days at 20oC but at Bay or ocean temperatures larval development probably
takes 30 to 40 days. C. franciscorum reached maturity within 9 to 12 months from
hatching. Males mature at approximately 37 mm TL and most live only one year while
females mature at approximately 48 mm TL and live one to two years.
Annual abundance of immature C. franciscorum has been highest in years with high
freshwater outflow and was relatively low through the 1987-1992 drought.
Note that although the abundance of C. franciscorum increased in 1993 from 1992, the
1993 index was low relative to previous years with high freshwater outflow. With the
addition of 1993, the relationship between annual abundance of immature C. franciscorum
and outflow remained strongly positive, although the correlation coefficient decreased
from 0.874 to 0.756 (see graph). Broodstock abundance may have limited production of
immature C. franciscorum in 1993, as the abundance of mature C. franciscorum was the
lowest for the study period.
Annual abundance indices for Crangon franciscorum
are generated from the San Francisco Bay Monitoring Program
using otter trawl data.
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