11.9° to 20.9° C for exposure times of 5, 30, and 60 

 min. The lowest AT at which 100% mortality was 

 observed was 15.8° C. This occurred in larvae 

 exposed 30 and 60 min. In the case of the 5 min 

 exposure, some larvae survived up to a 19.4° C AT 

 before experiencing 100% mortality. There was a 

 high background mortality in these experiments 

 which was probably due to stress resulting from 

 the immediate transfer of larvae to seawater 1 d 

 prior to treatment. This was not an unnatural 

 stress, however, since in nature the larvae are 

 immediately washed from the brook into the es- 

 tuary, <50 m away, once they hatch from the adhe- 

 sive eggs. 



Discussion 



The larvae of all three species appear to be able 

 to survive AT's of short duration which are near 

 the upper limits of cooling systems in most nor- 

 mally operating nuclear power plants (18.6° C, 

 Schubel et al. 1978). Our results show that the 

 Atlantic herring larvae are much more tolerant to 

 brief (< 60 min) increased temperature exposures 

 than to the longer term exposure (24 h) reported 

 by Blaxter (1960). It should be noted that Atlantic 

 herring larvae are usually older and developed 

 beyond the yolk-sac stage when they arrive at the 

 inshore nursery areas from the spawning grounds 

 and the results of these experiments should be 

 considered in light of that fact. Smooth flounders, 

 on the other hand, spawn in the estuaries and 

 inshore areas of the Gulf of Maine and the larvae 

 are susceptible to entrainment by power plants at 

 an early age.^ These larvae have a greater thermal 

 tolerance than Atlantic herring and appear to be 

 able to survive AT's in excess of those normally 

 encountered during entrainment. Rainbow smelt 

 larvae differ from both the Atlantic herring and 

 smooth flounder. Rainbow smelt normally spawn 

 in freshwater brooks during April and May in 

 coastal Maine and almost immediately upon 

 hatching the larvae are swept downstream into 

 saltwater where they experience a sudden in- 

 crease in salinity. The rainbow smelt larvae which 

 we tested in brook water showed thermal toler- 

 ances very similar to smooth flounder larvae but 



those tested in seawater showed the lowest tem- 

 perature tolerance of all the experiments. It 

 appears, then, that if rainbow smelt larvae are 

 entrained at this time the effects of increased sa- 

 linity might act synergistically with the tempera- 

 ture increase to produce a lethal stress. 



Acknowledgments 



This work was supported by a grant from the 

 Maine Yankee Atomic Power Company. 



Literature Cited 



BARKER, S. L., AND J. R. STEWART. 



1978. Mortalities of the larvae of two species of bivalves 

 after acute exposure to elevated temperature. In L. D. 

 Jensen (editor), Proceedings of the Fourth National Work- 

 shop on Entrainment and Impingement, p. 203-210. E. A. 

 Communications, Melville, N.Y. 

 BLAXTER, J. H. S. 



1960. The effect of extremes of temperature on herring 

 larvae. J. Mar. Biol. Assoc. U.K. 39:605-608. 

 SCHUBEL, J. R., C. C. COUTANT, AND P M. J. WOODHEAD. 



1978. Thermal effects of entrainment. In J. R. Schubel 

 and B. C. Marcy, Jr. (editors). Power plant entrainment, a 

 biological assessment, p. 19-93. Acad. Press, N.Y. 

 SHELBOURNE, J. E. 



1964. The artificial propagation of marine fish. Adv Mar. 

 Biol. 2:1-83. 



SETH L. BARKER 



DAVID W. TOWNSEND 



JOHN S. HACUNDA 



Department of Oceanography 

 Ira C. Darling Center 

 University of Maine at Orono 

 Walpole, ME 04573 



■Lindsay, P,S.L. Barker, and J. R.Stewart. 1978. Section 4. 

 Monitoring of the effects of the condenser cooling water system 

 on plankton and larval organisms. In Final report, environ- 

 mental surveillance and studies at the Maine Yankee Nuclear 

 Generating Station, 1969-1977, p. 4.1-4.1.135. Maine Yankee 

 Atomic Power Company, Augusta, Maine. 



FOOD OF 10 SPECIES OF NORTHWEST 

 ATLANTIC JUVENILE GROUNDFISH 



The food of fishes in the northwest Atlantic has 

 been studied over many years. Verrill (1871) was 

 one of the first investigators to document the food 

 of marine fish. Recent investigations have identi- 

 fied the food of commercially important fish or fish 

 currently composing a large portion of the fish 

 biomass in the northwest Atlantic (Edwards and 

 Bowman 1979; Langton and Bowman 1980), but 

 still little is known about the diet of juvenile 

 groundfish. 



Most groundfish larvae are wholly planktonic 

 until they either become demersal or grow large 



200 



FISHERY BULLETIN: VOL. 79, NO. 1, 198L 



