HETTLER and CHESTER: WINTER TEMPERATURE AND SPRING LANDINGS OF PINK SHRIMP 



lished by NOAA Environmental Data and Infor- 

 mation Service, National Climatic Center, Ashe- 

 ville, N.C. Weekly mean air temperatures were 

 calculated by averaging daily maximum and 

 minimum records. Rainfall records for Decem- 

 ber, January, and February were totalled for 

 each winter. 



The commercial landings of pink shrimp (kilo- 

 grams of abdomens) were obtained from records 

 published by the U.S. Department of Commerce 

 (North Carolina Shrimp Landings, Current 

 Fisheries Statistics series) (Table 1). Landings 

 from late winter through July of each year com- 

 prised the portion of the fishery considered by 

 our hypothesis to be influenced by severe over- 

 wintering conditions, primarily extensive peri- 

 ods of low temperatures and, possibly, reduced 

 salinities. Landings after July were excluded be- 

 cause, in late summer, size and weight decreased, 

 reflecting recruitment of postwinter juveniles 

 into the estuary. 



RESULTS AND DISCUSSION 



Annual Temperature Cycle in 

 the Newport River Estuary 



Weekly mean water temperatures in the New- 

 port River estuary displayed a basically sinus- 

 oidal annual pattern (Fig. 2). Actually there ap- 

 peared to be a slight distortion in the seasonal 



sine relationship whereby vernal warming pro- 

 ceeded at a slower rate than autumnal cooling. 

 Available data from 1962 to 1981 were used to 

 mathematically define the annual temperature 

 cycle according to the following least-squares, 

 multiple regression equation: 



T w = a + bi SIN 



2jrW 

 52 



+ b 2 COS 



2jtW 

 52 



where Tw was the mean weekly temperature for 

 week W, a was an intercept reflecting the overall 

 average yearly temperature, and b\ and b 2 were 

 regression coefficients controlling the timing 

 and amplitude of annual minimum and maxi- 

 mum temperatures. 



The derived equation (Fig. 2) was an adequate 

 representation of the annual cycle of tempera- 

 ture in the Newport River estuary (R 2 = 0.93) and 

 helped illustrate several aspects of the plotted 

 data. Minimum temperatures tended to occur 

 during the 5th week of the year (early February); 

 maximum temperatures occurred during the 

 31st week (mid-August). Winter temperatures 

 were characterized by greater week-to-week 

 variability than summer temperatures. In gen- 

 eral, the fitted curve consistently overestimated 

 winter temperatures. This trend arose from an 

 apparent asymmetry of the minimum and maxi- 

 mum temperatures about the yearly mean. That 



Table 1.— Landings of pink shrimp in North Carolina compared with various combinations 

 of winter water temperature data collected at Pivers Island, N.C, and air temperature and 

 rainfall data collected at Morehead City, N.C. Air temperature biweekly periods corre- 

 sponded with the coldest two consecutive weeks used for water temperature. 



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