FISHERY BULLETIN: VOL. 74, NO. 1 



Table 7. — Comparisons of mean total length (cm) of penaeid shrimps between subareas 

 (Tukey's u;-procedure) of the St. Andrew Bay system, Fla., from September 1972 through 

 August 1973. 



Species 



Subareas, mean total length in parentheses, and significance lines' 



df 



'Any two means not underscored by the same line are significantly different at the 5% level. 



tions, and river discharges are lower in the St. 

 Andrew Bay system than in other northern gulf 

 estuaries (Apalachicola Bay to the Rio Grande 

 River). The dominant group of spermatophytes in 

 the lower area are the submerged sea grasses, 

 whereas in most other northern gulf estuaries the 

 dominant groups are the emergent grasses in the 

 intertidal zone (Kutkuhn 1966). This unusual es- 

 tuarine environment in the St. Andrew Bay sys- 

 tem may induce shrimps of the genus Penaeus to 

 remain within the system for longer periods of 

 time, especially in the lower areas where oceanic 

 conditions often prevail. 



Such environmental differences probably ac- 

 count for the differences observed in composition, 

 abundance, and size of penaeid shrimps between 

 the St. Andrew Bay system and other estuarine 

 systems in the northern Gulf of Mexico. For 

 example: 1) large adult (total length ranges of 

 16.5 to 18.5 cm) P. duorarum and P. aztecus usu- 

 ally occur only in offshore waters, but we caught 

 many of these large specimens throughout the St. 

 Andrew Bay system; 2) in low salinity waters 

 characteristic of other bay systems subadult P. 

 setiferus and P. aztecus are more abundant than 

 P. duorarum, whereas in the St. Andrew Bay 

 system we found subadult P. duorarum more 

 abundant than P. setiferus and P. aztecus; and 3) 

 previous reports indicated that T. similis, S. 



brevirostris, and .S. dorsalis do not ordinarily 

 enter estuaries (Eldred 1959; Joyce 1965; Kut- 

 kuhn 1966; Cobb et al. 1973), but we caught many 

 individuals of these species within the St. Andrew 

 Bay system. 



The abundance of shrimps of Trachypenaeus 

 and Sicyonia in the St. Andrew Bay system con- 

 trasts sharply with those reported from other 

 estuarine areas of the Gulf of Mexico. Other in- 

 vestigators have included catches made adjacent 

 to barrier islands or tidal passes and reported 

 abundances of less than 1 shrimp per tow. (Dun- 

 ham 1972; Gunter 1950; Saloman 1964, 1965; 

 Swingle 1971). In our study, average catch per tow 

 (excluding Station 6, which is adjacent to a bar- 

 rier island) for each species was: T. similis, 36; T. 

 constrictus, 8; S. brevirostris, 19; S. dorsalis, 21. 



Periods of greatest abundance of S. brevirostris 

 in offshore waters of the northwestern and south- 

 eastern gulf occur in summer and early fall 

 (Brusher et al. 1972; Cobb et al. 1973). In the St. 

 Andrew Bay system, this species was almost ab- 

 sent during this period. We believe that this 

 shrimp migrates from inshore to offshore gulf 

 waters during spring months. 



Means and ranges of total lengths of species of 

 Trachypenaeus or Sicyonia taken in other es- 

 tuarine areas were usually less (Swingle 1971; 

 Dunham 1972) than those taken in offshore areas 



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