TIDES 



Tidal flushing in Charlotte 

 Harbor is subject to long term 

 cycles. One of these cycles lasts 

 for 8.86 years with a 4.43 year span 

 for coincidence of perigee and the 

 farthest northerly and southerly dis- 

 placement of the moon relative to 

 earth's equator. An analysis of the 

 maximum predicted daily ebb-tide 

 range from 1970 to 1980 suggests that 

 the average annual ebb-tide range can 

 vary by about 10 percent or 6 cm. 

 The minimum range occurred in 1977. 



Flushing in Charlotte Harbor, 

 as influenced by river flow and tidal 

 exchange apparently was near a mini- 

 mum in 1977. A dry season followed 

 by a dry, wet season should result in 

 evaporation exceeding precipitation, 

 coupled with low river flows and a 

 minimum exchange between the estuary 

 and gulf, salinities should rise in 

 the harbor. The longest duration of 

 high salinities occurred in 1977 

 (Figure 7) . 



FISH ABUNDANCES 



Mean abundances for the five 

 years averaged by month show the 

 annual tendencies for each species 

 (Table 3). The very dry, dry season 

 of 1976-1977 was followed by an 

 extremely dry, wet season (Tables 1 

 and 2). During the driest wet season 

 (1977) seven taxa (L. xanthurus , A. 

 felis , ■ L. rhomboides , B. marinus , T. 

 P. scitulus 



maculatus , 



and 



plagiusa ) showed abundances not ex- 

 ceeded in any other wet season (Table 

 4). Bagre marinus showed the great- 

 est dry season abundance in the 

 following dry season, unlike the 

 other two species more common in the 

 wet season. Three of these four taxa 

 with usual dry season preference (L. 

 rhomboides , S. plagiusa , and P. 

 scitulus) showed abundance in the 



following dry season greater than all 

 other dry seasons (Table 5). The 

 presence of L. rhomboides during the 

 past five years was basically re- 

 stricted to the wet season of 1977 

 and the following dry season. 



Influence of one season's abun- 

 dance on the following dry season 

 appears to be of short duration. 

 Species abundances in the following 

 dry season, 1977-1978, were apparent- 

 ly influenced by the unusual wet sea- 

 son abundances. However, this dry 

 season was also relatively wet and 

 that may have been a confounding 

 influence. The wet season of 1978 

 showed no apparent influence from the 

 preceding wet or dry seasons of 1977- 

 1978. 



The wet season of 1976 was 

 usually low in relative abundance 

 (Table 4). This may be the result of 

 early and high sustained flows that 

 produced adverse conditions or rates 

 of change in Charlotte Harbor salin- 

 ity and dissolved oxygen (Figure 7). 

 Flows greater than those observed in 

 June 1976 have occurred about 27 per- 

 cent of the time (Figure 3). This 

 could mean that relative abundances 

 may be as low as or even lower than 

 those observed in 1976 for the upper 

 part of the harbor about 27 percent 

 of the time. 



Among the abundant taxa, some 

 species were not collected during 

 some seasons. Two species were not 

 collected at all during the wet sea- 

 son of 1976 and another three species 

 were represented by a total of five 

 specimens (Table 6). In the 1975 wet 

 season three taxa were rare and two 

 were absent. One to three taxa in 

 the remaining wet season were rare or 

 absent. One to four taxa were rare 

 during dry seasons. Taxa frequently 

 showing seasonal rarity were L. 

 rhomboides , B. marinus and E. gula . 

 Lagodon rhomboides probably is not a 



307 



