MOYLE ET AL.: NONCOEVOLVED ASSEMBLAGE OF ESTUARINE FISHES 



Table 3. — Spearman rank correlation coefficients between fish species ranked by month by numbers and other variables 



ranked by month. Underlined values are significant at P > 0.05. 



flows occurred from August through October. Sali- 

 nity, temperature, and Secchi depth were generally 

 lowest (0-1 ppt, 8°-ll°C, and 17-18 cm, respective- 

 ly) when outflows were highest, and highest (4-9 ppt, 

 19°-23°C, and 25-40 cm, respectively when outflows 

 were lowest. There is, however, considerable year- 

 to-year variation in these cycles. When outflows were 

 comparatively low (1979, 1981), salinities, temper- 

 atures, and turbidities peaked at higher levels than 

 they did in high outflow years. Because 1982 and 

 1983 were exceptionally wet years, virtual freshwater 

 conditions prevailed throughout both years. 



Invertebrates 



Neomysis mercedis became very abundant in the 

 marsh from April to June, but the population de- 

 clined rapidly through the summer, reaching a low 

 in October (Fig. 2). This pattern fits with previous 

 studies of this species, which showed that its popula- 

 tions generally followed the mixing zone up and 

 down the estuary and were reduced at temperatures 

 higher then 22°C and salinities >7 ppt (Orsi and 

 Knutson 1979). In this study, N. mercedis abundance 

 showed a significant positive correlation with out- 

 flows and significant negative correlations with tem- 

 perature, salinity, and turbidity (Table 4). It also 

 showed a significant negative correlation (Table 3) 

 with two of its major predators in the marsh, striped 

 bass and yellowfin goby (Herbold 1985 4 ). 



Palaemon macrodactylus and Crangon francis- 

 corum also showed seasonal patterns of abundance 

 (Sigfreid 1980), but the patterns were much less 

 marked than those of N. mercedis. Palaemon macro- 

 dactylus were most abundant during July through 

 October and least abundant during January and 

 February, while C. franciscorum were most abundant 

 in November and December and least abundant in 

 January through March. Palaemon macrodactylus 

 abundance therefore showed strong positive corre- 

 lation with temperature and salinity and a negative 

 correlation with outflows. Crangon franciscorum 

 abundance was also negatively correlated with 

 outflows, but had a positive correlation only with 

 salinity. 



Fishes 



A total of 42 species, represented by about 67,000 

 individuals, were collected in the 1,238 trawl hauls 

 made during the study. The four measures of overall 

 fish abundance and diversity showed negative cor- 

 relations with month series and with years, in- 

 dicating a general decline through the study period 

 (Table 4, Fig. 3). Numbers, biomass, and number of 

 species had positive correlations with temperature 

 and/or salinity and negative correlations with out- 



"Herbold, B. 1985. Resource partitioning within a non-co- 

 evolved assemblage of fishes. Unpubl. Ph.D. Thesis, Univ. Califor- 

 nia, Davis. 



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