VARIATION IN FRESHWATER INFLOW AND CHANGES 

 IN A SUBTROPICAL ESTUARINE 

 FISH COMMUNITY 



Thomas H. Fraser 



Environmental Quality Laboratory, Inc. 

 1767 S. Tamiami Drive 

 Port Charlotte, Florida 33952 



ABSTRACT 



INTRODUCTION 



Trawl-susceptible fishes have 

 been sampled for five years in Char- 

 lotte Harbor, Florida. During this 

 period, freshwater inflow recorded on 

 the Peace River has varied from the 

 second lowest to near the mean flow 

 for the past 49 years. The 12 most 

 abundant of 43 taxa captured, com- 

 prising about 98 percent of the total 

 catch, were used in the detailed 

 analysis with flow. Average seasonal 

 abundance appeared to be inversely 

 related to flow in the wet season and 

 directly related to flow in the dry 

 season. Strong correlations exist 

 for flow in June and the average 

 abundance for June through September, 

 and also for December-January flows 

 and the average abundance for 

 December through May. Apparent 

 cycles of flow with an average period 

 of six years occur in each season. 

 The wet season of 1977 may represent 

 a minimum point in the wet season 

 cycles. A predicted astronomic 

 tidal effect with a period of 8.86 

 years reached a minimum in 1977. 

 Relative abundance during the wet 

 season of 1977 was higher than all 

 other wet seasons and may have 

 influenced abundances in the dry 

 season of 1977-1978. 



In the Apalachicola drainage 

 basin (Meeter et al., 1979), varia- 

 bility in abundance may be affected 

 by long-term periodic changes of 

 regional (local) climate. The long- 

 term data of Livingston et al. (1978) 

 show a correlation between river flow 

 and fish abundance. This study and 

 others such as Livingston et al. 

 (1976) in the Apalachicola estuarine 

 system provide the nearest (geograph- 

 ic) long-term data on fishes and 

 physical factors to this study. 



A study of upper Charlotte 

 Harbor has been underway for five 

 years. Flow characteristics of the 

 Peace River and the subtropical cli- 

 mate of the estuarine area are much 

 different (Taylor, 1974) from those 

 described by Livingston and other 

 workers for the Apalachicola, yet the 

 faunas are similar. 



This report briefly addresses 

 the following topics: (1) the rela- 

 tionship of abundance in Charlotte 

 Harbor to Peace River flow; (2) tem- 

 poral variation in abundance; (3) the 

 relationship of abundance to other 

 factors, such as temperature; and 

 (4) long-term patterns that might 



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