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



Waters in the St. Andrew Bay system are rela- 

 tively high in transparency. This high transpar- 

 ency results in part from the porosity of the soils 

 of the watershed, the low freshwater inflow, and 

 the proximity of the system to the clear waters of 

 the northeastern Gulf of Mexico. In terms of ex- 

 tinction coefficients, the transparency of gulf 

 waters adjacent to St. Andrew Bay are typical of 

 clear oceanic waters (Tolbert and Austin 1959). 



The bottom of the bay system is composed of 

 distinct sediment regimes. The sand regime 

 (>80% sand) is generally restricted to areas near 

 the passes and in depths less than 6 m. The silt- 

 clay regime (>50% clay, <50% silt, and <20% 

 sand) is located in the deeper waters of the sys- 

 tem, but not in the passes (Waller 1961). 



The bay system also contains areas covered by 

 rooted submerged vegetation. The submerged 

 vegetation includes turtle grass, Thalassia tes- 

 tudinum; manatee grass, Syringodium filiforme; 

 and shoal grass, Diplanthera wrightii. These 

 grasses cover an area of about 3,200 hectares. 



METHODS 



Sampling was conducted every 2 wk from 6 

 September 1972 through 21 August 1973 at 12 

 stations (Figure 1, Table 1). Two consecutive 

 nights were required to sample at all stations 

 with samples taken between sunset and 0200 h. 

 On 23-24 August 1973 additional sampling was 

 conducted between 1000 and 1400 h at the 12 sta- 

 tions to compare day catches with the night 

 catches of 20-21 August 1973. 



Biological samples were obtained at each sta- 

 tion with an 11.5-m wing trawl with stretched 

 meshes of 7.6 cm in the wings, 3.8 cm in the body, 

 and 2.5 cm in the cod end. The trawl was towed at 

 about 3.5 knots for 10 min. The entire catch at 

 each station was placed on ice and transported to 



Table l. — Locations and depth ranges of sampling stations in 

 the St. Andrew Bay system, Fla. 



the laboratory and frozen. Catches were thawed 

 and processed usually within 1 wk of collection. 

 Penaeid shrimps from each sample were enumer- 

 ated by species, and 30 individuals, or all if less 

 than 30, were measured to the nearest 0.5 cm 

 total length (tip of rostrum to tip of telson). 



Environmental data were also obtained at each 

 station. A water sample for determining dis- 

 solved oxygen and turbidity was taken 0.5 m 

 above the bottom at each station with a 3-liter 

 water sampler Salinity and temperature were 

 determined in situ with a Beckman^ RS5-3 por- 

 table salinometer (accuracy ±0.5°C and ±0.31,) 

 at the above mentioned depth. Turbidity was 

 determined with a Hach turbidimeter (Formazin 

 turbidity units — accuracy ±0.02 FTU), and dis- 

 solved oxygen determined by the modified Wink- 

 ler method (accuracy ±0.05 ml/liter). 



For each species, differences in catch per unit 

 effort (average catch per tow), and in size (aver- 

 age length by date) between subareas were tested 

 statistically with Tukey's a;-procedure (Steel and 

 Torrie 1960). For length comparisons, data were 

 used for only those dates when shrimps of a 

 species were caught in all subareas. For compari- 

 sons of distribution and abundance, the data were 

 grouped into the following subareas: East Bay 

 (stations 1, 2); North Bay (station 12); West Bay 

 (stations 10, 11); St. Andrew Bay (stations 3-5, 

 7-9); and East Pass (station 6). 



Mean catches per tow and mean total lengths 

 were also compared between upper and lower bay 

 areas. The upper area included all stations in 

 East Bay, North Bay, and West Bay, and the lower 

 area included all stations in St. Andrew Bay and 

 East Pass. 



ENVIRONMENTAL FACTORS 



Mean values of environmental factors near the 

 bottom were determined for subareas. Salinities 

 and dissolved oxygen were higher in St. Andrew 

 Bay and East Pass than in the other subareas 

 (Table 2). Turbidities in North Bay, East Bay, and 

 West Bay were greater than in St. Andrew Bay 

 and East Pass. Bottom temperatures, however, 

 were similar among subareas. 



When subarea data were combined into the re- 

 spective upper and lower areas, the average val- 

 ues were: salinity— 29.2, 33.2%; turbidity— 3.0, 



'United States Department of Commerce, Nautical Chart 868-SC. 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



159 



