THE EFFECTS OF FRESHWATER DISCHARGES ON SPORTFISHING 

 CATCH RATES IN THE ST. LUCIE ESTUARY, MARTIN COUNTY, FLORIDA 



Eleanor Van Os , Joseph D. Carroll, Jr., and James Dunn 



U.S. Fish and Wildlife Service Ecological Services 

 Post Office Box 2676, Vero Beach, Florida 



ABSTRACT 



The St. Lucie River is a 6,000- 

 acre estuary located on the east 

 coast of Florida. It is the eastern 

 outlet of fresh water released from 

 Lake Okeechobee through the St. Lucie 

 Canal. The primary purpose of the 

 releases is for flood control. 

 Neighboring communities depend heavi- 

 ly on tourism and are concerned 

 about the effects that the freshwater 

 discharges and associated silt loads 

 have on fishing success. A creel 

 census was conducted by the U.S. Fish 

 and Wildlife Service for one year. 

 Multiple-source, stepwise regression 

 analysis and ridge regression analy- 

 ses were performed on the freshwater 

 discharge and creel data to determine 

 if catch rates are affected by the 

 St. Lucie Canal discharges, and, if 

 so, in what part of the estuary they 

 are affected. It was determined that 

 snook, croaker, sheepshead, mullet, 

 black drum, weakfish, gafftopsail 

 catfish, gray snapper, and Irish 

 pompano catch rates were significant- 

 ly affected by moderate discharges. 



INTRODUCTION 



The St. Lucie River is a small 

 estuary of approximately 6,000 acres 

 located in Martin and St. Lucie 



counties on the southeast coast of 

 Florida. The North and South Forks, 

 constituting the inner estuary, con- 

 verge at the City of Stuart, where 

 the river widens to one mile after 

 passage beneath the Roosevelt Bridge. 

 Approximately three miles east, the 

 river bends to the south, extending 

 to the southernmost extension of 

 Sewall Point, a spit of land separat- 

 ing the St. Lucie River from the 

 Indian River (a coastal lagoon) to 

 the east. At this point, both bodies 

 of water empty into the Atlantic 

 Ocean at the St. Lucie Inlet (Figure 

 1). 



Fresh water enters the St. Lucie 

 Estuary from three natural sources: 

 direct rainfall runoff and ground- 

 water seepage. Three man-made drain- 

 age canals add to the drainage area 

 that already includes parts of Okee- 

 chobee, Martin, and St. Lucie count- 

 ies. The St. Lucie Canal, which dis- 

 charges into the South Fork, is of 

 primary concern in this study as one 

 of the major outlets for regulatory 

 discharges from Lake Okeechobee. 



Historically, Lake Okeechobee 

 overflowed infrequently into the 

 Everglades in the southern part of 

 the State. As the population in- 

 creased south of Okeechobee and hur- 

 ricane flood damages occurred, with 

 need for more predictable drainage 

 became apparent. A state agency, 



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