high metabolic rate of juveniles and 

 consequently their greater osmoregu- 

 latory capabilities is an important 

 factor in maintaining this distribu- 

 tion. It seems likely that this is 

 also an important mechanism for 

 insuring larval protection and sur- 

 vival. Maintaining an optimum areal 

 coverage of oscillating salinity 

 habitat therefore seems most cri- 

 tical to maintenance of estuarine 

 fish production (Browder and Moore 

 1980). 



If this oscillating salinity 

 zone is the major "production" area 

 of the estuary (Browder and Moore 

 1980), some changes in fish produc- 

 tion capacity of the study area are 

 imminent. Recall that mean salini- 

 ties have been rising in Whitewater 

 Bay due to upstream watershed modi- 

 fication, thus reducing the range 

 and availability of this production 

 zone. 



Signs of such changes have, in 

 fact, already been documented. They 

 include a general decline in fishery 

 harvests during recent years (Ever- 

 glades National Park 1979) and 

 shifts in population structure and 

 abundance of key sport fishes (Davis 

 1980). According to Davis (1980) at 

 least three significant changes have 

 occurred in fisheries of the area 

 during the past 20 years: 



(1) age structure shifts in red 

 drum and spotted sea trout 

 toward larger, more mature 

 individuals; 



(2) catch rates have consis- 

 tently risen for red drum 

 and fallen for spotted sea 

 trout; 



(3) year to year variability in 

 catch rates for both species 

 has been markedly reduced. 



These changes presumably result 

 from a combination of (1) rainfall 

 shortages; rainfall has been below 



normal for 16 of the last 20 years 

 in south Florida, and (2) upstream 

 water diversion; the watershed has 

 been reduced from 22,500 km 2 

 (8,688 mi 2 ) to approximately 2,059 

 km 2 (795 mi 2 ) (Davis and Hilsen- 

 beck, 1974). 



Table 31 presents a compilation 

 of the data of Clark (1971) and 

 Jannke (1971) with regard to spawn- 

 ing times of estuarine fish that are 

 believed to follow the general model 

 of offshore spawning by adults with 

 subsequent migration by larvae to 

 estuarine waters. No doubt the data 

 are incomplete and preliminary, but 

 they do present a framework for 

 generating some healthy speculation 

 on the potential effects of changing 

 physical/chemical conditions. 



7.34 AMPHIBIANS AND REPTILES 



Odum et al. (1982) list 24 spe- 

 cies of amphibians and reptiles from 

 the Florida mangrove zone, consider- 

 ably less than the 65 species listed 

 by SFRC (1980) for the terrestrial 

 and freshwater wetlands. All the 

 species that occur in the mangrove 

 zone are also reported from other, 

 upland habitats. 



Using five trophic delineations 

 (herbivore, omnivore, primary, 

 middle, and higher carnivore), the 

 amphibians and reptiles of the man- 

 grove zone fall into an interesting 

 pattern (Table 32). The predomi- 

 nantly water based group is more or 

 less trophically restricted to the 

 lower end, receiving nourishment 

 from vegetation, benthic mollusks 

 and invertebrates, or a combination 

 thereof. Among those more dependent 

 on land or wetland, trophic struc- 

 turing is clearly restricted to the 

 primary, middle, and higher carni- 

 vore levels. Insects, small mam- 

 mals, birds, and fish form the bulk 

 of these species' diets. 



159 



