stand higher temperatures than those in the lower 

 portions of the tidal zone and these in turn gen- 

 erally can withstand higher temperatures than the 

 same species of animals living in the subtidal 

 zones. In addition, when considering the coastline 

 as a whole, we must recognize that there are vari- 

 ous races within a given species which may vary 

 considerably in their environmental requirements, 

 or in their ability to withstand extreme conditions. 



In our marine waters, there is a great mixture 

 of species. Species typical of higher latitudes are 

 found with species that are more abundant farther 

 south. Tropical or subtropical species generally 

 will spawn in the summer months. Species from the 

 higher latitudes require low water temperature for 

 spawning and the development of the young. Thus, 

 they usually spawn in the winter months and tem- 

 peratures at that time are critical. Any warming of 

 the water during the cold weather or winter pe- 

 riod could be disastrous from the standpoint of the 

 elimination of the more northerly species. In some 

 instances, a rise in winter temperatures of only 2 

 or 3 F might be sufficient to prevent spawning and 

 thus eliminate these species from the biota. 



In the northern portions of the country there is 

 generally a great range in natural temperatures. In 

 southern areas, as we approach the tropics, we find 

 smaller overall temperature ranges. In the tropics 

 or subtropics, optimum temperatures for many 

 forms are only a few degrees lower than maximum 

 lethal temperatures. Great care should be exer- 

 cised, therefore, to prevent harmful increases in 

 maximum summer temperatures in tropical areas. 



In general, temperatures in the marine waters 

 do not change as rapidly nor do they have the 

 overall range from extreme to extreme as they do 

 in fresh waters. Marine and estuarine fishes, there- 

 fore, are less tolerant of temperature variation. 

 They can accommodate somewhat, but overall 

 temperature range and rate of change are even 

 more important here than they are in fresh waters. 

 It has been observed that when surface water tem- 

 peratures over the Georges Bank increased from 

 46 to 68 F, the larval fish died at 65 F. It has been 

 found that species in subtropical and tropical en- 

 vironments are living at temperatures that are only 

 a few degrees less than their lethal temperatures. 

 In the most northern forms, extensive variations 

 in seasonal temperatures are a necessity for orderly 

 development and growth. Spawning and develop- 

 ment frequently occur at lower temperatures and 

 the sexual products ripen on rising temperatures 

 after a period of low temperatures. Temperatures 

 above or below the optimum range may delay or 

 speed up development. They may inhibit swim- 

 ming ability and the effectiveness of food utiliza- 



tion may be decreased with increasing tempera- 

 tures in the upper viable range. Fishes and other 

 forms are also more susceptible to parasites and 

 diseases at temperatures outside of their optimum 

 range. In regard to rapid changes in temperature, 

 it has been found that a drop in temperature from 

 58 to 43 F kills sardines. Tolerable temperature 

 minima vary with the population and its past tem- 

 perature history. Kills have occurred off the Texas 

 coast at 40 F whereas kills of the same species 

 have occurred off Bermuda at a drop to 59 F. 

 Many kills have occurred in nature due to unusu- 

 ally low temperatures. Kills also occur due to 

 natural high temperatures. Yellowtail flounder and 

 whiting larvae died when they drifted from an area 

 of 44 F to one of 64 F. It has been reported that 

 61 F is best for the developing of mackerel, but 

 70 F is too high. These are merely illustrations of 

 what might happen to species occurring in inshore 

 waters. 



It is apparent from the foregoing that data are 

 very sparse on temperature requirements of marine 

 and estuarine species. It is very difficult, therefore, 

 to attempt to suggest temperature requirements 

 for marine and estuarine forms. The difficulty is 

 compounded by the great extent of the Nation's 

 shorelines, the differing natural temperature varia- 

 tions from north to south, and the geographic over- 

 lapping of species native to different latitudes. 

 Consideration must be given to maximum allow- 

 able temperatures for both the summer period and 

 the winter period. 



In attempting to establish permissible levels of 

 temperature increase in receiving waters due to 

 heated waste discharges, precaution must be taken 

 to prevent — 



(a) excessive incremental increases above 

 background values even though such in- 

 cremental increases lie below maximum 

 limits, and 



(b) exceeding maximum natural background 

 limits. 



Such precautions are necessary to prevent grad- 

 ual net increases in background temperatures due 

 to the continuously increasing volumes of heated 

 wastes being discharged into receiving waters. 



The discharge of heated wastes into estuaries 

 and other tidal tributaries must be managed so that 

 no barrier to the movement or migration of fish 

 and other aquatic life is created. 



Recommendation: In view of the requirements for 

 the well-being and production of marine organisms, it 

 is concluded that the discharge of any heated waste 

 into any coastal or estuarine waters should be closely 

 managed. Monthly means of the maximum daily tem- 

 peratures recorded at the site in question and before 



462-246 0-72-6 



69 



