MOYLE ET AL.: NONCOEVOLVED ASSEMBLAGE OF ESTUARINE FISHES 



Suisun City* 

 Pey tonia 



Study 

 Area 



Figure 1.— Locations of sample sites (*) in Suisun Marsh, Sacramento-San Joaquin Estuary, CA. 



During this study, two major habitat types were 

 sampled: 1) small dead-end sloughs that were 7-10 

 m wide and 1-2 m deep and 2) Suisun Slough, which 

 connected all the dead-end sloughs and was 100-150 

 m wide and 2-4 m deep. A third habitat, Montezuma 

 Slough, was also sampled, but the data were not used 

 here because our methods did not sample it ade- 

 quately. This slough is deep (3-4 m), wide, and 

 riverlike; it is the marsh's main source of freshwater. 



METHODS 



Sampling was conducted monthly at seven loca- 

 tions throughout the marsh (Fig. 1), from January 



1979 through June 1983, with the exception of 

 December 1979 and October 1980. Four of the loca- 

 tions were in dead-end sloughs (Peytonia, Boynton, 

 Mallard, and Goodyear), one was a small slough open 

 at both ends (Cutoff), and two were in Suisun Slough. 

 Sampling was conducted biweekly from January 



1980 through June 1981, but the samples for each 



month were lumped together for analysis, as the 

 samples within months were comparable All samples 

 were taken during the day, as 24-h studies conducted 

 in April 1979 and 1980 did not exhibit any signifi- 

 cant differences between day and night samples. 

 The principal means of sampling was a four-seam 

 otter trawl with a 1 x 2.5 m opening, a length of 

 5.3 m, and mesh sizes that tapered down to 6 mm 

 stretch in the bag. At each location, the trawl was 

 towed for either 5 min (small sloughs) or 10 min 

 (Suisun Slough) at about 4 km/h. The longer periods 

 were necessary in large sloughs because of the small 

 catches that prevailed there Each location was sam- 

 pled at least twice on each date This method of 

 sampling was biased because large fishes probably 

 avoided the trawl, and fishes that favor the emergent 

 vegetation were undersampled, as were fishes in the 

 upper part of the water column (Kjelson and Colby 

 1977). However, these problems were minimized by 

 the narrowness and shallowness of most of the 

 sampling sites; in any case such biases were consis- 



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