A model for exploring the impact of radiation on fish populations

In the general context of protecting the biotic environment, it is frequently the population of organisms at which it is intended that protective measures should be directed. It is well-established, however, that exposure to low-level, chronic irradiation can affect the survival and reproductive capacity of individual plants and animals. Although it is clear that such effects can have implications for the well-being of the populations, it is less apparent (and almost certainly not the case) that the radiation can affect population attributes directly, i.e., without the mediation of effects in individuals. The problem is, therefore, to establish criteria for the limitation of effects in individuals such that the population will also be sufficiently protected. Before this can be achieved, it is necessary to have a means of relating the known effects of radiation in individuals with their possible consequences for the population. A simple Leslie matrix population model approach has been developed to investigate how the effects of radiation in individuals may propagate to produce (or not) a response at the population level. Different species can have different reproductive strategies and life cycles, and may, therefore, respond differently to the same degree of radiation effect on survival and reproductive capacity. It is of interest to investigate their possible responses at the population level, and the matrix population model approach is here applied to two somewhat contrasting fish species - the plaice (Pleuronectes platessa) and the thornback ray (Raja clavata). The results from the models appear to confirm the relative sensitivities of the two populations, as might be predicted on the basis of their life cycles and reproductive strategies, to the possible effects of radiation on individual fertility, fecundity and mortality. (author)