To date, about 109 species of fish have been collected from 
the Bay. These species have been distributed among 43 different 
families. More importantly, it appears that fish abundance and 
distributions are related to freshwater inflow from the Delta. 
For example, of the 58 species looked at so far, 24 demonstrated 
a "wet response" to flow. In other words, these species were 
caught in greater numbers during wet years. Twenty-two species 
showed a mixed response, while only 12 showed a dry response 
(Table 1). 
Table 1. Number of species with highest catches during 
various year types. 
Salinity Preference Wet 
_ Group _ Response 
Freshwater 3 
Anadromous 3 
Estuarine 5 
Marine-Estuarine 2 
TOTAL 24 
Mixed 
Response 
3 
3 
2 
4 
22 
Dry 
Response 
2 
1 
0 
2 
12 
A surprising thing was learned upon further analysis of 
these same data when individual species responses were cate¬ 
gorized (Table 2). Only one species in the top 15 most abundant 
species demonstrated a dry response. That species was the 
jacksmelt. This is interesting because one would expect greater 
numbers of marine species in the Bay during dry years. This did 
not occur. It is also interesting to note the estuarine species 
response (Table 2). Four of the five estuarine species col¬ 
lected occurred in the top 15 of the most abundant species in 
the Bay, and all of those species demonstrated a wet response 
showing the importance of freshwater flows to these types of 
species in San Francisco Bay. 
It also appears that outflow affects Bay shrimp abundance in 
San Francisco Bay. Abundance indices for this species were 
greater during wet years than during dry years. Preliminary 
study results also have led to the conclusions that some fish 
appear to be more widely distributed during wet years. 
There are two reasons why fish may change their 
distribution. First of all, they may change distribution 
because of salinity alterations. Salinity may increase or 
decrease above or below species salinity preferences and cause 
them to move to another area. 
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