Low-temperature tolerance of overwintering white shrimp (<i>Litopenaeus setiferus</i>) in South Carolina
Subadult white shrimp, <i>Litopenaeus setiferus</i>, overwinter in estuarine waters, where they are vulnerable to cold kills when water temperature decreases rapidly. This has direct impacts on the season opening and level of harvest of the spring fishery, so proper management of this species requires a thorough understanding of the effects of cold water temperatures on survival. Low-temperature tolerance of overwintering white shrimp collected in Charleston Harbor, South Carolina was determined using three experimental methods: the chronic lethal method (CLM), the acclimated chronic exposure (ACE) method with static temperatures, and the ACE method with fluctuating temperatures. These methods all use an environmentally realistic temperature decline of 1<sup>o</sup> C/day. Using the CLM, shrimp exposed to constantly declining temperatures (n=133) were found to experience loss of equilibrium at a mean temperature (± SD) of 6.87<sup>o</sup> C ± 1.50<sup>o</sup> C and mortality at a mean temperature of 3.82<sup>o</sup> C ± 0.54<sup>o</sup> C. The ACE method, which uses changing temperatures until a base temperature is reached, was used to evaluate how white shrimp were affected by exposure to prolonged (10-d), sub-lethal temperatures, and daily temperature fluctuations characteristic of estuarine environments. The ACE method was performed with both static and fluctuating temperatures, at three base temperatures (8.5<sup>o</sup> C, 7<sup>o</sup> C, and 5.5<sup>o</sup> C). Shrimp exposed to static temperatures of 8.5<sup>o</sup> C, 7<sup>o</sup> C, and 5.5<sup>o</sup> C (n=72, n=67, n=71) had significantly different survival rates (P < 0.001), with 10% , 24%, and 99% mortality respectively. Temperature fluctuations around both an 8.5<sup>o</sup> C and 7<sup>o</sup> C base temperature did not significantly affect time until loss of equilibrium or mortality compared to the static treatment at the same base temperatures; however temperature fluctuations caused significantly higher mortality for the 5.5<sup>o</sup> C base temperature (P < 0.0001). These data will be used to develop predictive mortality estimates for overwintering subadult white shrimp (80-110 mm) and will validate the use of temperature as a proxy for mortality in current management practices.