sand-shell mixture. The most common macro- 

 invertebrates in the area were pink shrimp, 

 arrow shrimp ( Tozeuma carolinense ), and the 

 portunid crab ( Portunus gibbesi ). 



The station in Old Tampa Bay is off the 

 southwestern edge of Courtney Campbell Park- 

 way in fairly turbid water of 2 to 3 m. depth, 

 and minor tidal currents (0.5 knot; U.S. Coast 

 & Geodetic Survey, 1951). Mean salinity was 

 22.7 p.p.t., and the range was 19.6 to 25.4 

 p.p.t. The bottom lacked attached vegetation, 

 but several species of red and green algae 

 ( Gracilaria spp. and Ulva lactuca Linnaeus) 

 were noted occasionally. Bottom sediments 

 were a silty-sand mixture. The most abundant 

 macroinvertebrates in the area were pink 

 shrimp, blue crab ( Callinectes sapidus ), and 

 squid ( Lolliguncula brevis)--Dragovich and 

 Kelly (1964). 



Results of systematic sampling to determine 

 the diel habits of pink shrimp have not been 

 reported previously, although Eldred, Ingle, 

 Woodburn, Hutton, and Jones (1961) made 

 limited observations in Tampa Bay. 



PROCEDURE AND EQUIPMENT 



The two stations were occupied eight times 

 each for 24-hour periods in alternate months 

 from August 1962 through December 1963. 

 Shrimp were taken at 3-hour intervals with a 

 4.9 m. (16-ft.), nylon, semiballoon shrimp 

 trawl of 3.8 cm. (1-1/2 inch) stretch mesh 

 webbing in the body and bag, and an inner 

 liner of 1.2 cm. (l/2-inch) stretch mesh in 

 the cod end. Tows were made for 10 minutes 

 at 3 to 4 knots from the R. V. Kingfish . 



Hydrological measurements were made 

 prior to the collection of shrimp samples. 

 Salinity samples were taken with modified Van 

 Dorn sampling bottles (Van Dorn, 1957) and 

 analyzed according to the methods described 

 by Saloman, Finucane, and Kelly (1964). Water 

 temperature was taken with a Whitney 1 

 underwater thermistor. A Kahl submarine 

 photometer equipped with deck and sea cells 

 was used to measure light intensity in micro- 

 amps for later conversion to percentage light 

 transmission. Water samples and measure- 

 ments were taken at surface, middepth, and 

 bottom. 



Shrimp were preserved in 10 percent buf- 

 fered formalin immediately after collection. 

 Later, the carapace length was measured with 

 vernier calipers and the sex determined. 



DIEL FLUCTUATIONS OF CATCH 



AND SIZE OF PINK SHRIMP IN 



RELATION TO LIGHT 



At Egmont Key, 779 pink shrimp were caught 

 (table 1) along with specimens of Trachypeneus 



sp. and Sicyonia sp. In the same period and with 

 identical effort and procedures, 454 pink 

 shrimp were caught in Old Tampa Bay (table 2). 



Table 1. — Pink shrimp caught during diel sampling at ^jmont Key, Fla. 



Table 2. — Pink shrimp caught during diel sampling in Old Tampa Bay, Fla. 



1 References to trade names In this publication do not 

 Imply endorsement of commercial products. 



Catches of shrimp at both stations were in- 

 versely related to the amount of light trans- 

 mitted to the bottom (fig. 2). The nocturnal 

 catch (2100, 2400, and 0300 hours) at Egmont 

 Key accounted for 87 percent of the total 

 catch at this station; catches in "marginal" 

 light (1800 and 0600 hours) and daylight (0900, 

 1200, and 1500 hours) accounted for 11 per- 

 cent and 2 percent. In Old Tampa Bay the 

 nocturnal catch was 67 percent and the catches 

 by daylight and marginal light were 18 per- 

 cent and 15 percent. Pink shrimp are gen- 

 erally considered nocturnal (Eldred, et al., 

 1961; Fuss and Ogren, 1966; and others), but 

 a few daytime captures have been recorded 

 in muddy water, during ground swells, or 

 under cloudy skies (Eldred, et al., 1961; 

 Hildebrand, 1955; and Fuss, 1964). Altough 

 the water is shallower in Old Tampa Bay than 

 at Egmont Key, the periods of light intensity 

 are less sharply defined in Old Tampa Bay 

 because of the higher turbidity (table 3). 



Although pink shrimp are far more active 

 at night than during the day, Aaron and 

 Wisby (1964) reported that in laboratory ex- 

 periments more than half of the shrimp in the 



