BRUSHER and OGREN: PENAEID SHRIMPS IN ST. ANDREW BAY SYSTEM 



in these values occurred in the salinity of the 

 upper area where heavy spring rains accounted 

 for an exceptional drop in salinity in early April. 

 Compared to hydrological data from other 

 northern gulf estuaries (Gunter 1950; Swingle 

 1971; Dunham 1972; Stokes 1974), the values 

 within the St. Andrew Bay system are more 

 oceanic than estuarine (Waller 1961; Hopkins 

 1966). 



CATCHES 



Eight species of penaeids were taken during 

 the study: three species ofPenaeus (P. duorarum, 

 P. aztecus, and P. setiferus), two species of 

 Trachypenaeus (T. similis and T. constrictus) , and 

 three species of Sicyonia iS. breuirostris, S. dor- 

 salis, and S. typica). Catches of each species at 

 each of the 12 stations are shown in Table 3. The 

 greatest number of individual shrimps (species 

 combined) was taken at station 4 (St. Andrew 

 Bay), the least at station 2 (East Bay). Penaeus 

 duorarum was the most abundant species, S. 

 typica the least. Since only 25 S. typica (ranging 

 in size from 3.5 to 5.5 cm) were caught, this 

 species will not be discussed in the following 

 sections. 



Although methods were similar, a striking dif- 

 ference was apparent between our catches and 

 those from other estuarine systems in the north- 

 ern Gulf of Mexico. In our study, 57.6% of the 

 total penaeid catch consisted of members of the 

 genus Penaeus, 22.6% of the genus Sicyonia, and 

 19.7% of Trachypenaeus. In contrast, studies in 

 other estuarine systems in Alabama (Swingle 

 1971), Louisiana (Dunham 1972), and Texas 

 (Gunter 1950; Moffett 1968; Stokes 1974) showed 



that the genus Penaeus represented 99 to 100% of 

 the total trawl catch of penaeids. 



DISTRIBUTION AND 

 ABUNDANCE 



To determine where shrimp were more abun- 

 dant in the St. Andrew Bay system, relative 

 abundances were compared by subarea (Table 4). 

 Significant differences were found for four of the 

 seven species: T. similis, S. breuirostris, S. dor- 

 salis, and T. constrictus. Either St. Andrew Bay or 

 East Pass or both had significantly greater abun- 

 dance of these species than the other subareas. 



When subarea data were combined for each 

 species and apportioned into upper and lower 

 areas, the relative abundances were greater in 

 the upper area for P. aztecus and P. setiferus and 

 were greater in the lower area for the other 

 penaeids. Average catches per tow for the upper 

 and lower areas, respectively, were: P. duorarum, 

 110.8, 129.3; T. similis, 12.8, 49.4; S. breuirostris, 

 6.0, 51.3; S. dorsalis, 2.9, 32.9; T. constrictus, 3.1, 

 14.8; P. aztecus, 10.1, 4.6; P. setiferus, 2.7, 0.3. 



To determine seasonal distribution and abun- 

 dance, the catches per tow were calculated by 

 area and by date for each species. The results, 

 shown in Figure 3, indicate summer and fall 

 abundances for the three species of Penaeus, al- 

 though not necessarily in both areas. For Trachy- 

 penaeus and Sicyonia, seasonal abundances were 

 evident only in the lower area, with T similis and 

 S. dorsalis more abundant during spring and 

 summer, S. breuirostris more abundant during 

 winter and early spring, and T constrictus during 

 spring. 



Table 3. — Total numbers of penaeid shrimps caught in 312 trawl hauls within the St. Andrew Bay system, Fla., from September 1972 



through August 1973. 



161 



