FISHERY BULLETIN: VOL. 71, NO. 2 



creased predation resulting in decreased selec- 

 tion; increased fishing pressure. The potential 

 interactions among these processes are manifold. 

 Some are virtually mutually exclusive. For 

 instance a population explosion of predators 

 (including barred sand bass) is inconsistent 

 with a model based on decreased predation. 

 Some models have a superficial complementarity. 

 For instance, a general increase in marine 

 productivity, though resulting in population 

 growth, would not necessarily alter selection 

 against divergent phenotypes. Predator-prey 

 ratios, for instance, might be expected to remain 

 relatively constant. 



Most theories that would appear to explain 

 these data are based on a genetic hypothesis. 

 It is not easy to sustain these hypotheses in 

 view of the apparent age-dependency of the 

 asymmetry. Skeletal abnormalities in these 

 same fish (Valentine, in press) show similar 

 temporal and spatial patterns. We tentatively 

 conclude that the environmental stress hy- 

 pothesis gives the best fit to the data. It is very 

 possible that this approach may be limited in 

 application to the detection of stress induced by 

 agents affecting calcium metabolism, transport, 

 or deposition. Recent experiments, conducted 

 in our laboratory, with the fruit fly, Drosophila 

 melanogaster, re-emphasizes this point. We 

 attempted to increase the asymmetry of sterno- 

 pleural chaeta by raising fruit flies from eggs 

 to adults in culture medium treated with 

 various toxicants (methyl mercury chloride, 

 cupric sulfate, tetraethyl lead, and p,p'-DDT). 

 Toxicant concentrations ranged from 1 ppb 

 (part per billion) to lethality and egg concentra- 

 tions from 1 to 200 per vial. Results, in all 

 instances, were negative. 



Asymmetry analysis, if it proves fruitful for 

 measuring environmental stress, has some 

 important benefits. We think such an assay 

 would: 



1. permit continuous monitoring of the health 

 of biological communities via periodic checks 

 of specific sensitive organisms; 



2. permit the detection of long-term trends 

 (decades) by comparing preserved material with 

 contemporary materials; 



3. permit economies to be made in the moni- 

 toring of communities and; 



4. increase the lead time between the detec- 

 tion of significant biological changes and com- 

 munity morbidity. 



SUMMARY 



The data presented show two trends, an 

 increase in bilateral asymmetry with time and 

 a consistent spatial pattern. Data for grunion 

 and barred surfperch taken at one locality, 

 Belmont Shore, near Los Angeles, over two 

 decades clearly show increasing temporal asym- 

 metry values. Data from barred sand bass and 

 the other two species show increasing geo- 

 graphic trends from deep Baja California (an 

 area virtually uninhabited) to southern Cali- 

 fornia. Additionally, barred surfperch asym- 

 metry values decrease north of Los Angeles, 

 so that asymmetry is apparently not responding 

 strictly to a latitudinal trend. Several hy- 

 potheses were examined, and it is tentatively 

 concluded that environmental toxicant stress 

 is the likeliest explanation. 



We believe asymmetry analysis may be 

 developed into a useful tool for examining the 

 sublethal effects of multiple toxicants on 

 natural or laboratory populations. Such anal- 

 yses are relatively easy to perform and, thus, 

 offer significant advantages over other commonly 

 used assays. 



ACKNOWLEDGMENTS 



We would like to thank Allen Mearns, Irwin 

 Haydock, Stuart Brody, Edward Fager, and 

 John Isaacs for offering constructive comments 

 throughout the duration of this research. Their 

 suggestions were not always incorporated into 

 our research effort, so they are blameless for 

 any errors. We should also like to thank Ralph 

 Miller, Jr., of H & M Landing in San Diego, for 

 allowing D. W. Valentine to collect specimens 

 from his ships while operating in Mexican 

 waters. Without the support of H «& M Landing 

 and its personnel, it would have been impossible 

 for us to obtain many of our Mexican samples. 



Work contained herein was supported by 

 grants from the Marine Life Research Group 

 (Scripps Institution of Oceanography, No. 1273) 

 and a contract from the Southern California 



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