Potential effects of increase in solar ultraviolet radiation

SHORT COMMUNICATIONS surface, to provide a baseline from which to assess possible future environmental changes. This information would also aid the evaluation of present knowledge Life being a delicate balance between the beneficial relating the incidence of skin cancer to the amount of and detrimental effects of sunlight, the implications ultraviolet radiation received. Further studies should for human health and ecological systems of an in- be made with test animals to determine the dosecrease in solar ultraviolet radiation reaching the response characteristics of the ultraviolet radiation Earth's surface are matters of vital importance. They induction of skin cancer, the panel concluded. are expertly examined in a report released early in The effects of increased levels of ultraviolet radiation 1973 by an a d hoc panel of the Environmental Studies on biological systems other than Man may have Board of the US National Academy of Sciences and greater long-range significance than the problem of National Academy of Engineering. Copies of the human skin cancer, according to the report. Although report: 'Biological Impacts of Increased Intensities of definitive predictions are difficult, present information Solar Ultraviolet Radiation' (vii + 46pp., 3 figs, suggests that an increase in terrestrial solar ultraviolet 1973) are available from The National Technical radiation might diminish the biological productivity Information Service, 5285, Port Royal Road, Spring- of the oceans, interfere with mating and other behavioural patterns of insects and other lower animals, field, Virginia, USA. (Pub. No. PB215 524). Life on Earth is partially shielded from biologically- and damage plants---especially agricultural species. It harmful solar ultraviolet radiation by a thin layer of was further noted that most life-forms probably ozone in the upper atmosphere. The panel found that developed in prehistoric times after the formation of if jet engine exhausts from high-altitude flights should the ozone shield, the formation of this protective lessen the amount of ozone in the stratosphere, and shield presumably being a prerequisite for the evoluthereby increase the amount of solar ultraviolet tion and maintenance of terrestrial life. Biochemical repair mechanisms exist in most living radiation reaching the surface of the Earth, there would be a high probability of significant harm to things and provide a means of counteracting the humans and to other life-systems, although whether continuous natural damage and alteration of cells by the SSTs would significantly alter the ozone in the sunlight. One molecule easily altered by sunlight is deoxyribonucleic acid (DNA), which carries an stratosphere is still a subject of scientific debate.* Because of the radiation-absorbing properties of organism's genetic 'blueprint'. Increased amounts of ozone, a small decrease in ozone concentration would ultraviolet radiation may overload natural repair result in a large increase in ultraviolet radiation mechanisms, with serious consequences to biological reaching the Earth's surface in the wavelength range systems. This imbalance could, in the case of simple 280-320 nanometers (thousand-millionths of a metre). life-forms, cause the death of the organism or lead to A 5 per cent decrease in ozone concentration, for mutations in future generations, according to the example, would yield a 26 per cent increase in the report. Because laboratory tests indicate that, among plants, intensity of the most biologically-damaging ultraviolet radiation. This increase, it is estimated, would agricultural species are some of the most ultravioletproduce a minimum of 8,000 additional cases of the sensitive, the panel suggested that laboratory and field most common types of skin cancer per year in the studies be initiated on important agricultural plants, United States alone. The estimate is derived from to determine how they grow and produce under the progressively higher incidence of skin cancers near increased ultraviolet radiation. Certain forms of marine the Equator, where persons receive greater exposure to life, for example planktonic ones, also may be ensunlight and where, in addition, ultraviolet radiation dangered by increased levels of terrestrial ultraviolet radiation, the panel indicated. It recommended that is more intense than at temperate latitudes. The panel recommended gathering information on accurate measurements of the depth of penetration of the wavelength distribution and intensities of ultra- ultraviolet radiation in natural waters, and studies of violet radiation at several locations on the Earth's the reactions of marine life to increased ultraviolet intensities, be undertaken. Important effects of ultraviolet radiation in Man, * See Editorial on page 159.--Ed. 220 POTENTIAL EFFECTS OF INCREASE IN SOLAR ULTRAVIOLET RADIATION

Biological Conservation, Vol. 5, No. 3, July 1973--O Applied Science Publishers Ltd, England, 1973--Printed in Great Britain

221

Short Communications other than skin tumours, include sunburn and changes in the appearances of the skin, which are usually accepted as signs of ageing. Chemical agents such as certain antibiotics, diuretics, and tranquillizers, can increase a person's sensitivity to ultraviolet radiation by increasing the severity of a sunburn or by leading to an allergic reaction to sunlight. Other effects of ultraviolet radiation in Man, such as the killing of harmful Bacteria and the conversion in the skin of provitamin D to vitamin D, have usually been considered beneficial, but the panel asserted that the effects of increased amounts of ultraviolet radiation on these processes could not be accurately predicted from available information and might very well be detrimental. Too little is known of the interactions between environment, behaviour, and genetic background that determine an individual's reaction to sunlight. Therefore, the panel recommended studies designed to permit early recognition of persons especially susceptible to skin cancer. Further, the panel recommended that the public be made aware that, although all life on this planet ultimately depends on available sunlight, a balance exists between its beneficial effects in moderate amounts and its potential for harm in excess. ENVIRONMENTALSTUDIESBOARD,

National Academy of Sciences/ National Academy of Engineering, 2101 Constitution Avenue, Washington, D.C. 20418, USA.

THE ECOLOGY OF INTRODUCTIONS - - A CASE STUDY FROM THE AFRICAN LAKES

Dr Geoffrey Fryer (1972), in his paper on the longterm conservation risks which face the unique series of habitats and their living occupants in the great lakes of East Africa, includes a section on 'mismanagement of fisheries'. In particular he refers to the introduction of the large predatory Nile Perch (Lates niloticus) to Lake Victoria as 'a tragedy which a knowledge of even elementary biology would have warned its advocates to avoid'. The history of this case is illuminating, and the result is proving to be not so simple as Dr Fryer suggests. The Nile Perch and some other fishes which are today indigenous to the Nile from the Murchison Falls to the Delta, were exterminated from the upper Victoria Nile system, which includes Lakes Victoria and Kioga and their rivers above the Murchison Falls, probably during a period of desiccation. Lakes Victoria and Kioga subsequently developed a large

assemblage of mainly endemic species. Even before the first fisheries surveys of these lakes (Graham, 1929; Worthington, 1929), the introduction of Nile Perch above the Murchison Falls had been suggested, originally by keen anglers, as evolution in these isolated waters had failed to produce much in the way of sporting fish. At that time both Graham and I argued strongly against such an introduction. We used the same argument as Fryer, namely that the direct foodchain from Algae to fish, as illustrated by Tilapia, is more efficient as a fish-producing mechanism than an indirect one via predators. I did suggest, however, that it might be worth while to test this simple hypothesis by introducing Nile Perch to Lake Nabugabo in Buganda--a small and completely isolated lake which happens to contain a good sample of the Lake Victoria fauna. This experiment was never carried out but the advocacy for the introduction continued, using the additional argument that a reduction in the Tilapia fishery through over-fishing pointed to the growing importance of the numerous other species of fish. Only a few of these were caught commercially in significant quantity, but many others might be cropped through the agency of a large and easily-caught predator. Over some twenty-five years, the advice from qualified scientists was consistently against such an introduction, maintaining that the risks were too great, but, eventually, an experimental introduction was made-not to Lake Nabugabo or Lake Victoria, but to Lake Kioga--and this soon confounded the prognostications of the biologists. Since 1928 in Lake Kioga and its associated swamps there had developed by the 1950s a flourishing fishery for the indigenous species; this had risen to, and seemed to have become more or less stabilized at about 12,000 tons per annum. On first principles it was predicted that this might drop if, and when, the Nile Perch established itself. Within a few years of the introduction, however, far from a drop in the total tonnage, the Kioga fishery for the indigenous species continued at about the former very substantial figure, and, in addition, a very large tonnage was caught of Nile Perch, and of another fish, Tilapia nilotica, which had also been introduced from below the Murchison Falls. According to the Uganda Fisheries Department's annual report for 1970 (Uganda, 1971), the estimated total catch from the Lake Kioga area in that year reached a record, made up as follows (rounded figures): Indigenous fish

Tilapia nilotica Nile Perch Total

12,000 tons 16,000 tons 34,000 tons 62,000 tons