TRANS URANICS IN MARINE ENVIRONMENT 719 



stock may survive even thougli it is subjected to a total mortality rate of 60 to 70% per 

 year. Any additional mortality, say, due to radiation, would reduce the stock but would 

 not necessarily affect the ability of the stock to replace itself. Additionally, any mortality 

 caused by radiation would probably not be detectable as such. There are only a very few 

 studies on natural populations that have been subjected to low-level irradiation; but, in 

 those reported (Donaldson and Bonliam, 1964; 1970; Bonham and Donaldson, 1966; 

 Blaylock, 1961 ; Templeton et al, 1976), there is no evidence that low levels of radiation 

 have any adverse effects on these populations. 



There is virtually no pubUshed data on the genetic effects of irradiation on fish 

 populations. Although studies have indicated that chromosomal abnormalities can occur 

 in irradiated eggs and larvae of aquatic species (Ophel et al., 1976), there is no evidence to 

 indicate that these abnormalities have been detrimental to the population. Predictions 

 therefore can be based only on studies conducted with other species, e.g., Drosophila. It 

 can be argued from those data that modest increases in mutation rates with concomitant 

 enhancement in the genetic variability may even lead to improved fitness (Neel, 1972). 

 Additionally, the large amount of genetic variability revealed by recent biochemical 

 techniques may challenge the consensus that mutations are always detrimental in nature 

 and emphasize the importance of understanding the dynamics of newly introduced 

 mutants in tlie gene pool and selective processes. These developments have increased the 

 difficulty of assessing the potential long-term genetic implications of the irradiation of 

 natural populafions (Neel, 1972; International Atomic Energy Agency, 1976). In this 

 connection, Woodhead (1974) has conservatively estimated, on the basis of very limited 

 data, that, if all mutations are dominant lethals resulting in nonviable zygotes, then less 

 than 1 of every 1000 fish embryos would be eliminated as the result of an integrated dose 

 of 0.5 rad received by each of the parents. 



Research Needs 



Many assumptions used in considering the somatic and genefic effects of radiafion on 

 populations in the aquatic environment are to some degree speculative. Since this is also 

 true for assessments of the effects of any energy-related pollutants that enter the aquafic 

 environment, the recommendations for future research made by the International Atomic 

 Energy Agency (1976) could equally be appUed to pollutants other than radiation. 

 It is recommended that prime consideration be given to: 



• Comprehensive studies on a sufficient spatial and temporal scale to determine the 

 significance of changes in populations, communities, and ecosystems resulting from 

 low-level chronic exposure to pollutants, singly and in combination. Emphasis should be 

 given to determining the rates of change, the rates of recovery from various degrees of 

 damage, and tlie rates of repopulation in decimated areas. 



• Comparative studies of mutation rates induced by pollutants, singly and in concert, 

 on a wide range of marine organisms, including species with both high and low 

 fecundities. Emphasis should be given to both genetic damage (gene mutation, 

 chromosomal aberrations, recombination, etc.) and effects on population size, biomass, 

 fecundity, and fitness components. 



• Studies designed to provide an understanding of the role of genetic variation, 

 expressed as discrete polymorphisms and quantitative variations of individual species, in 

 the maintenance of aquatic communities. Emphasis should be given to clarifying the 

 significance of the response of these polymorphisms to varying physical, chemical, and 

 biological parameters. 



