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



Penaeid shrimps taken from the St. Andrew 

 Bay system showed definite habitat preference by 

 genera when abundance was related to depth. As 

 shown in Table 5, the higher mean catches per 

 tow for Penaeus occurred in the shallower waters, 

 while those for Trachypenaeus and Sicyonia oc- 

 curred in the intermediate and deeper waters of 

 the sampled area. Ninety -two percent of all Tra- 

 chypenaeus and Sicyonia were taken from the 

 lower area where the average station depth was 

 8.6 m. 



Day and night comparisons showed mean catch 

 per tow to be greater at night for all seven species 

 (Table 6). 



Table 5. — Comparisons of mean catch per tow and mean 

 length (cm) of penaeid shrimps in relation to depth and species 

 within the St. Andrew Bay system, Fla., from September 1972 

 through August 1973. 



Table 6. — Comparisons of mean catch per tow and mean total 

 length (cm) between day and night catches of penaeid shrimps 

 taken from the St. Andrews Bay system, Fla., in August 1973. 



Species 



Day 



Night 



Penaeus duorarum 

 Tracliypenaeus similis 

 Sicyonia brevirostns 

 S. dorsalis 

 T. constrictus 

 P. aztecus 

 P. setiferus 



No of tows 



12 



12 



SIZE 



Shrimps of the genus Penaeus were larger than 

 shrimps of the other two genera. Penaeus seti- 

 ferus had the largest mean length, while S. dor- 

 salis had the smallest. Mean total lengths in cen- 

 timeters and length ranges in centimeters for 



each species in the St. Andrew Bay system were: 

 P. duorarum, 9.5, 4.0-18.5; T. similis,6.6, 3.0-10.0; 

 S. brevirostris, 5.7, 2.8-9.5; S. dorsalis, 5.5, 2.0- 

 7.8; T. constrictus, 4.5, 2.5-8.0; P. aztecus, 12.4, 

 4.5-18.5; and P. setiferus, 13.3, 7.0-16.0. 



Differences in lengths of shrimps associated 

 with water depth were examined (Table 5); nota- 

 ble differences were discernible only for the genus 

 Penaeus, the larger specimens of which generally 

 were found in deeper waters. This relation has 

 also been reported by others (Lindner and Cook 

 1970; Cook and Lindner 1970; Costello and Allen 

 1970). Species of Trachypenaeus and Sicyonia 

 showed little difference in mean lengths with 

 water depths, although the largest mean sizes 

 were found in the deeper zone. 



Examination for differences in lengths associ- 

 ated with sampling at night and during the day 

 revealed clearly that hour of sampling had no ef- 

 fect on size of captured shrimps (Table 6). 



Comparisons of mean total lengths for the 

 seven species between those subareas from which 

 sufficient data were available showed that the 

 largest shrimps were in either St. Andrew Bay or 

 East Pass (Table 7). However, statistically sig- 

 nificant differences were found for only three 

 species: P duorarum, T. similis, and P setiferus. 



For five of the seven species, larger specimens 

 were caught in the lower area more often than in 

 the upper area. The situation was reversed for S. 

 brevirostris, whereas, for T constrictus the mean 

 sizes for the two areas were the same. Mean 

 lengths in centimeters by species between upper 

 and lower bay areas, respectively, were: P. 

 duorarum, 9.1, 9.9; T. similis, 6.4, 6.7; S. bre- 

 virostris, 6.3, 5.7; S. dorsalis, 5.4, 5.6; T. constric- 

 tus, 4.5, 4.5; P. aztecus, 11.9, 12.8; and P. setiferus, 

 11.7, 14.7. 



Shrimps of the genus Penaeus were almost con- 

 sistently larger in the lower area throughout the 

 year (Figure 4). As shrimps of this genus grow 

 larger, they tend to move into deeper, more saline, 

 and less turbid waters. 



When present in both areas at the same time, 

 the two species of Trachypenaeus were larger in 

 the lower area more often than in the upper, 

 whereas the reverse was true of the two species of 

 Sicyonia. 



DISCUSSION AND CONCLUSIONS 



In general, water depths and salinities are 

 greater, and turbidities, temperature fluctua- 



163 



