26 
Carter R. Gilbert 
Some of the information contained herein appears, in condensed 
form, in a chapter dealing with the zoogeography of the freshwater 
fishes of southeastern United States, from the Savannah River to Lake 
Pontchartrain (Swift et al. 1986). This in turn is included in a recently 
published book on North American freshwater fish zoogeography 
(Hocutt and Wiley, editors, 1986). The reader is referred to these refer- 
ence sources for further information on the overall relationships of the 
south Georgia-peninsular Florida fish fauna to those of other areas. 
This study was supported in part by National Science Foundation 
grant no. GB-1 1744. 
COMPOSITION, RELATIONSHIPS AND ORIGINS 
OF FISH FAUNA 
The area south of the Altamaha River and east of the Apalachicola 
River lies entirely below the Fall Line (Fig. 1), and may be termed the 
south Georgia-peninsular Florida faunal complex. 1 2 It is separated from 
the neighboring Altamaha-Ogeechee-Savannah faunal complex at a 
Jaccard coefficient of association level of about 0.42, and from the Apa- 
lachicola River fauna at a coefficient level of 0.29 (Fig. 2). The south 
Georgia-peninsular Florida complex may in turn be subdivided (at 
about the 0.53 level) into northern and southern segments. The former 
includes the St. Johns and Suwannee drainages, as well as other drain- 
ages to the north, whereas the latter consists of the remaining rivers of 
peninsular Florida. Although the St. Johns falls within the northern 
segment of this faunal complex, this is somewhat misleading in terms of 
the actual origin of the drainage and its fauna. The history of this 
drainage is complex, and its fauna could just as logically be included 
among those occurring in the drainages of southern peninsular Florida. 
Although 126 native fish species are known to occur in fresh waters 
of the area, only those species (72) that normally spend their entire lives 
in fresh water were included in my analysis. The other 54 are species of 
marine affinities, about half of which regularly enter fresh water, either 
to spawn or to spend much of their lives, and the others of which occur 
there on a more-or-less casual basis. This is by far the greatest number 
of marine species entering fresh water for any area of comparable size in 
North America, exclusive of Central America. The 72 species analyzed 
1 The Fall Line is a zone of abrupt topographic change, characterized in many places by 
waterfalls or rapids on the various streams, which marks the boundary between the 
Coastal Plain and Piedmont areas and represents the maximal extent of past sea-level 
incursion. 
2 Jaccard coefficients of association between river drainages were calculated using species 
presence and absence data (Sneath and Sokal 1973; Sepkoski and Rex 1974; Swift et al. 
1986). 
