short exposure to increased temperature on the 

 largest or the smallest euphausiids tested. Two 

 out of three groups tested for 15 min in early June 

 (the largest euphausiids) exceeded 50'7r mortality 

 after exposure to 26"C as did the two groups tested 

 in late July (the smallest euphausiids). 



D 



ISC us-sion 



The intake of a condenser cooling system may 

 entrain large quantities of euphausiids — 

 depending to some extent on the depth of the in- 

 take, the season of the year, and even the time of 

 the day. During the summer, fall, and winter, the 

 young euphausiids make diurnal vertical migra- 

 tions from the 50- to 100-m strata, rising daily to 

 the surface during the dark hours. After sexual 

 maturity in the early spring they descend even 

 deeper until they inhabit depths over 200 m dur- 

 ing their second winter. The following spring they 

 rise to the surface for the second time to breed. The 

 young euphausiids thus spend much of their first 

 year at depths above 50 m, and older adults are 

 again near the surface in the spring (Ponomareva 

 1963). 



Gilfillan (1972) pointed out that E. pcuifica is 

 widely distributed and is abundant in water hav- 

 ing differing temperature characteristics. His 

 studies showed that E. pcuifica from the Pacific 

 Ocean were more easily stressed by changes in 

 temperature and salinity than those from the west 

 entrance of Strait of Juan de Fuca — which, in 

 turn, were more readily stressed than those from 

 Saanich Inlet. His results indicate that E. pcuifica 

 from inner Puget Sound would be among the most 

 resistant to thermal stress of these different 

 groups. 



Temperatures encountered by euphausiids in 

 Puget Sound normally vary only slightly from the 

 surface to 100 m and deeper. From October 

 through about May there is usually no change in 

 temperature from the surface to 100 m, whereas in 

 the summer the surface to 10 m or less may be a 

 few degrees warmer (Lincoln and Collias^). 



Seasonal temperature variations in most of 

 Puget Sound are also small, ranging from a low of 

 7°or 8°C in February to 11°C in late July, August, 

 and September. Even considering their vertical 

 migrations in summer, euphausiids are normally 



^Lincoln, J. H., and E. E. Collias. 1970. Skagit Bay Study 

 Progress Report No. 3. Univ. Wash. Dep. Oceanogr., Seattle, 

 Ref. M70-111, 88 p. 



subjected to only slight temperature fluctuations 

 and, therefore, the mortalities observed at simu- 

 lated condenser cooling temperatures are not sur- 

 prising. 



Once entrained in a condenser cooling system, 

 the euphausiids would encounter an abrupt tem- 

 perature increase of 12°-16"C (Coutant 1970), 

 which could increase temperatures above the am- 

 bient temperature of Puget Sound to the critical 

 range for survival. There are periods from July 

 through September when surface temperatures 

 may reach or exceed 15°C in portions of Puget 

 Sound (Lincoln and Collias see footnote 2). Nor- 

 mally, surface temperatures do not exceed 14°C. 

 Cooney ( 1971) noted high surface temperatures in 

 June of 16.7°- 19°C. These temperatures could re- 

 sult in condenser cooling temperatures of 27°C and 

 above, which this study found to be 1007f lethal in 

 a very short time. 



Data from this study indicate that even a short 

 passage time through a condenser (15 min) at 

 temperatures of 23°-24°C could kill from 11 to 53V. 

 of the euphausiids by thermal causes alone. The 

 added loss due to abrasion, pressure, and toxic 

 substances is unknown. 



To minimize damage to the euphausiid popula- 

 tions, condenser cooling system intakes should be 

 located deep enough to take advantage of the cold- 

 est cooling water available to minimize tempera- 

 tures in the system. A very deep intake (just below 

 100 m) would probably minimize the entrainment 

 of euphausiids. A surface intake would be espe- 

 cially harmful because of the higher surface tem- 

 peratures and because of the swarming of 

 euphausiids on the surface. Plant lights at night 

 could cause the surface swarming. 



Literature Cited 



Cooney, R. T. 



1971. Zooplankton and micronekton associated with a dif- 

 fuse sound-scattering layer in Puget Sound, Washing- 

 ton. Ph.D. Thesis, Univ. Washington, Seattle, 208 p. 



COL'TANT. C. C. 



1970. Entrainment in cooling waters: Steps toward pre- 

 dictability. Proc. 50th Anna. Conf. West. Assoc. State 

 Game Fish Comm,, p. 90-105. 

 CR.'SiDDOCK. D. R. 



1976. Effects of increased water temperature on Daphnia 

 putex. Fish. Bull., U.S. 74:403-408. 

 GILFILLAN E. 



1972. Reactions of Euphausia pad fica Hansen (Crustacea) 

 from oceanic, mixed oceanic-coastal and coastal waters of 

 British Columbia to experimental changes in tempera- 

 ture and salinity. J. Exp. Mar. Biol. Ecol. 10:29-40. 



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