BREWER: THERMAL TOLERANCE AND RESISTANCE 



high and low temperatures, resulting in the dis- 

 ruption of basic physiological functions such as 

 osmoregulation, respiration, and overall nervous 

 system integration (Prosser 1973). 



It is unlikely that the offshore realm of any 

 ocean could ever be significantly affected by arti- 

 ficial thermal input. Projected energy needs for 

 the decades ahead and their associated require- 

 ments for immense volumes of water for cooling 

 (electric power generating) and heating (LNG) 

 may pose a serious environmental threat in near- 

 shore areas, especially bays, harbors, and es- 

 tuaries. As a case-in-point, juvenile northern an- 

 chovy find the confined waters of the Los 

 Angeles-Long Beach Harbor a suitable habitat. 

 Brewer (1975a) found anchovy egg densities as 

 high as 35/m^ of surface water within 0.5 mile of 

 the harbor breakwater. These areas will be af- 

 fected by seawater intake pipes, and thermal 

 effluent plumes and E. mordax embryos would be 

 highly susceptible to entrainment. Eggs in the 

 blastodisc stage are most sensitive to abrupt 

 changes in temperature. If one considers the high 

 temperature extremes where mortality begins to 

 exceed the control mortality as unsafe, anchovy 

 embryos should not be allowed to remain in tem- 

 peratures of 35.5°, 30.5°, 30.0°, and 27.5°C for 

 periods longer than 1, 3, 5, and 60 min, respec- 

 tively. While embryos proved insensitive to the 

 effects of temperatures as low as 0.5°C for 60-min 

 exposures, it is questionable whether these sensi- 

 tive developmental stages could withstand the 

 turbulence and mechanical shock associated with 

 heat exchange systems or thermal effluent out- 

 falls. In this respect, larvae are most vulnerable, 

 and Lasker (1964) found this vulnerability in- 

 creased with decreasing temperatures below 14°C 

 for Pacific sardine, Sardinops, larvae which are 

 morphologically similar to anchovy larvae. Their 

 thin integument and fragile bodies are easily 

 damaged. Extreme care was taken in the present 

 study when the larvae were transferred from in- 

 cubation to test jars, but control survival was only 

 77.5%. Survival of larvae in experiments that did 

 not involve transfer to rearing vessels was over 

 90%. Serious consideration must therefore be 

 given to the location of intake pipes and effluent 

 discharge to avoid trapping eggs and larvae. These 

 stages are probably too small to be excluded by 

 screening. 



Many more experiments are required to under- 

 stand the dynamics of the thermal requirements of 

 E. mordax. It may be unreasonable to assume that 



there is one optimal temperature for anchovy 

 well-being. Activity cycles or rhythms (e.g., the 

 evening spawning cycle) may be present in 

 natural populations which require diel tempera- 

 ture changes (e.g., achieved through vertical mi- 

 gration). Temperature optima for reproduction or 

 the gi'owth of larvae in the yolk-sac stage may 

 differ from optima for growth of juveniles and 

 adults which must respond to fluctuating food 

 levels. Brett et al. (1969), experimenting with On- 

 chorhynchus nerka, found that as food rations 

 were decreased, temperatures required for 

 maximum growth rates also decreased. When food 

 rations were not limiting, growth rates increased 

 as the temperature increased to a certain optimal 

 level, after which growth rates decreased rapidly. 



In conclusion, the potential responses of the 

 northern anchovy to temperature are many and 

 varied. They depend upon the degree and rate of 

 temperature change, length of exposure to a par- 

 ticular temperature, the previous thermal experi- 

 ence of the fish, and the effects of interactions 

 among other environmental variables, both biotic 

 and abiotic. Furthermore, these responses vary 

 with ontogeny. 



Although expatriated individuals may tem- 

 porarily tolerate environmental extremes, the dis- 

 tribution and survival of E. mordax are ultimately 

 dependent upon those physicochemical charac- 

 teristics of the environment conducive to spawn- 

 ing. For the present, such an environment is best 

 described as that part of the California Current 

 where surface water temperatures reach 13°-18°C 

 during at least part of the year (Ahlstrom 1956, 

 1959, 1966, 1967; Richardson 1973). 



ACKNOWLEDGMENTS 



The discussions and criticisms of Basil G. Naf- 

 paktitis, Gerald J. Bakus, John E. Fitch, Bernard 

 W. Pipkin, and Camm C. Swift are gratefully 

 acknowledged. Without the interest and coopera- 

 tion of William Verna, a live-bait dealer at Long 

 Beach, Calif., this study would not have been pos- 

 sible. Special thanks go to Dorothy Soule and 

 Mikihiko Oguri for their support and confidence. 



The work was funded, in part, by NOAA-Sea 

 Grant (No. 04-3-158-36 and 04-3-158-45); the 

 Army Corps of Engineers; the Resources Agency, 

 State of California; the Pacific Lighting Service 

 Company; and a Grant-in-Aid of Research from 

 the Society of Sigma Xi. 



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