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196L The fauna of oyster beds, with special reference to 

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 WENNER, E. L., AND D. F. BOESCH. 



1979. Distribution patterns of epibenthic decapod Crus- 

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Fish Wildl. Serv., Fish. Bull. 65, 298 p. 

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1968. New records of brachyuran decapod crustaceans 

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 Reprinted 1973 as Sea Grant Publ. UNC-SG-73-02, 129 p. 



AUSTIN B. WILLIAMS 



National Marine Fisheries Service Systematics Laboratory 

 National Museum of Natural History 

 Washington, DC 20560 



David McN. Williams 



North Carolina Marine Resources Center 



Bogue Banks 



Atlantic Beach, NC 28512 



MORTALITIES OF ATLANTIC HERRING, 

 CLUPEA H. HARENGUS, SMOOTH FLOUNDER, 

 LIOPSETTA PUTNAMI, AND RAINBOW SMELT, 



OSMERUS MORDAX, LARVAE EXPOSED 

 TO ACUTE THERMAL SHOCK 



Entrainment of larval fishes through condenser 

 cooling systems of electric generating stations 

 often results in acute physical, chemical, and 

 thermal stresses. These stresses are often lethal 

 and the resulting mortalities could have adverse 

 effects on populations proximal to the cooling 

 v^rater intake site. This is particularly true for 

 fishes which have planktonic larvae (Schubel et al. 

 1978). 



The rapid increase in temperature associated 

 with passage through condenser cooling systems 

 is seldom if ever experienced by organisms in the 



natural environment. Little is known of the abil- 

 ity of the larvae of most species offish to withstand 

 this kind of thermal stress. In assessing thermal 

 stresses it is important not only to investigate the 

 effect of different increases in temperature from 

 some base temperature (AT), but also to investi- 

 gate the effect of the duration of the exposure. The 

 simplest simulation experiment, then, is one in 

 which larvae are exposed to a rapid increase in 

 temperature, are held at the elevated temperature 

 for a period of time, and are then returned rapidly 

 to the original base temperature. 



Our experiments were designed to evaluate the 

 thermal tolerances of three species of larval fish 

 occurring in the Gulf of Maine and its estuaries: 

 Atlantic herring, Clupea h. harengus, smooth 

 flounder, Liopsetta putnami, and rainbow smelt, 

 Osmerus mordax. These fish, although differing 

 somewhat in their life histories, are all common in 

 inshore areas during some part of their larval life, 

 and are therefore subject to power plant entrain- 

 ment. This paper presents the results of thermal 

 tolerance experiments which encompassed the 

 range of temperatures planktonic organisms en- 

 counter in condenser cooling systems. 



Methods 



All larvae used in the experiments were reared 

 in the laboratory. Atlantic herring eggs and milt 

 were stripped from ripe adults captured off 

 Gloucester, Mass. The eggs were fertilized and 

 held in 2 1 shallow glass bowls of filtered seawater 

 (31.8 L) at approximately the ambient tempera- 

 ture where the adults were collected (8°±1° C). 

 Most of the larvae hatched after 13 d. Ripe adult 

 smooth flounder were collected from Montsweag 

 Bay, part of the Sheepscot River estuary, Maine. 

 Eggs and milt were stripped from the adults, the 

 eggs fertilized, and also kept in 2 1 shallow glass 

 bowls of filtered seawater (25.51.) at the ambient 

 temperature (4°±1° C). The larvae began to hatch 

 after 21 d but the majority hatched after 27 and 

 28 d. Fertilized rainbow smelt eggs were collected 

 directly from a spawTiing site in Wiley Brook, a 

 tributary of the Damariscotta River estuary, 

 Maine. The eggs were kept in 40 1 aquaria with 

 filtered brook water at the ambient temperature 

 (13°±1° C). The brook water was treated with 

 streptomycin and penicillin according to methods 

 described in Shelbourne (1964) and malachite 

 green hydrochloride was added to control fungal 

 growth. Some of the rainbow smelt larvae began to 



198 



FISHERY BULLETIN: VOL. 79, NO. 1, 1981. 



