December to May. Flows in June and 

 December plus January are poorly cor- 

 related with subsequent seasonal 

 flows for the period of record (R 

 values less than 0.3). 



Perhaps long-term trends might 

 occur for abundances of fishes in the 

 upper third of Charlotte Harbor as a 

 result of specific variations in riv- 

 er flow. If the general trends ob- 

 served for this data set are descrip- 

 tive for relationships between flow 

 and abundance, then one might expect 

 average abundance to follow the 

 flows. Thus, for wet season average 

 abundance would be inversely related 

 to flow in June (Figure 8) and dry 

 season average abundance directly re- 

 lated to flow in December-January 

 (Figure 9) . 



Comparisons of relative abun- 

 dances showed that among the top six 

 species in Apalachicola Bay (Sheridan 

 and Livingston 1979), three were 

 among the top six in Charlotte Harbor 

 ( Anchoa mitchilli Leiostomus xanthu - 

 rus and Cynoscion arenarius ) . In both 

 estuaries mitchilli was most abun- 

 dant. The abundance pattern of A. 

 mitchilli was apparently different in 

 Charlotte Harbor with peaks in Feb- 

 ruary and June rather than October- 

 November in Apalachicola Bay. Cynos- 

 cion arenarius was abundant in Char- 

 lotte Harbor during the summer with 

 peaks in June and August, rather than 

 May and August. Leiostomus xanthurus 

 was abundant in Charlotte Harbor from 

 April through August with peaks in 

 April-May and July, rather than in 

 March. 



the end of declining temperature in 

 the dry season, were correlated with 

 fish abundance. 



2. Extremely dry, wet seasons 

 are accompanied by obvious increase 

 in the abundance of very common 

 species as well as the appearance of 

 species not abundant during wetter 

 wet seasons. 



3. Changes in abundance during 

 extremely dry, wet seasons may in- 

 fluence abundance in the following 

 dry season. 



4. Extremely cold temperatures 

 can temporarily influence abundance 

 and presence 

 periods . 



of taxa for short 



5. Long-term periodicity in 

 river flow may average about six 

 years for both wet and dry seasons. 

 The amplitude in flows may be quite 

 variable . 



6. Coincidence of other regu- 

 lar long-term cycles such as tidal 

 flushing may enhance environmental 

 changes produced by fluctuating river 

 flow. 



7. It seems reasonable to 

 expect some supra-annual oscillation 

 in fish abundance related to changes 

 in flow. The limits of variation are 

 not clear, for the data only approach 

 the known low-flow spectrum but are 

 not even close to the known high-flow 

 spectrum. 



CONCLUSIONS AND RECOMMENDATIONS 



Upper Charlotte Harbor 



1. Year-to-year variation in 

 river flow, particularly during the 

 beginning of the wet season and near 



Charlotte Harbor and Apalachicola Bay 



1. At least some of the more 

 common taxa in both estuaries show 

 abundance patterns that are dis- 

 similar in time. These differences 

 could be an expression of the varia- 

 tion in the physical characteristics 

 of the estuaries without implying 



318 



