The results of our first experiment in applying fertilizers to a small sealoch, Loch Craiglin (Gross, 1947; Marshall, 1947; Orr, 1947; Raymont, 1947; for references see No. V), were sufficiently encouraging to justify an extension of the work to a larger area. Loch Craiglin provided a good site for preliminary investigations because it could be easily enclosed and, for all practical purposes, isolated from the main loch. The conditions in Loch Craiglin were, however, atypical in many respects, and it seemed desirable that the results obtained there should be tested by investigations in a body of water (1) sufficiently large to reduce the extreme fluctuations in salinity, pH and other factors, encountered in Loch Craiglin; (2) sufficiently deep to reduce the proportion of seaweed to phytoplankton in the productivity of the cultivated area; and (3) with its connection with the main loch or the sea left undammed, to test the possibilities of fertilizer application in open, i.e. not artificially enclosed, sea-lochs.

1. The site (Kyle Scotnish) of an experiment to test the effect of the addition of chemical fertilizers (N and P) to an arm of a sea-loch is described.

2. Certain physical conditions of the loch are recorded, including the tides, which were of a peculiar form.

3. Methods used in the measurement of water movements are described, and the results used to calculate the rate of exchange of Kyle Scotnish water with the water outside the loch. At spring tides this exchange was estimated at less than 8 per cent, of the volume of Kyle Scotnish.

4. The additional corroborative evidence obtained by tracking marked water masses within the loch is presented.

5. The quantities of fertilizer used are tabulated, and results given which demonstrate its rapid removal from the water.

6. The significance of the low rate of water exchange is discussed. This low rate of exchange makes possible the increase in productivity of Kyle Scotnish, brought about by the addition of chemical fertilizers.

1. The phytoplankton in Kyle Scotnish and Sailean More, two parallel arms of Loch Sween, was studied and the seasonal variations described.

2. Artificial fertilizers were distributed in Kyle Scotnish and their effects on the phytoplankton were followed up. It was found that on some occasions the phytoplankton increased rapidly after the distribution of fertilizers, but that on other occasions there was no apparent response.

3. The zooplankton populations in Kyle Scotnish and Sailean More were studied and the seasonal variations described.

4. It was found that after fertilizers had been distributed the zooplankton in Kyle Scotnish became considerably richer than that in Sailean More, and its density remained higher until it was reduced in September 1945 by the feeding of young herring. Even so, the average density in Kyle Scotnish was twice that in Sailean More.

5. Experiments were done to determine the effect upon the phytoplankton of the grazing of the zooplankton. It appears that the zooplankton removed a large portion of the phytoplankton by grazing, and that the apparent lack of response of the phytoplankton to the distribution fertilizers was at least on some occasions due to the effects of grazing.

6. It was shown that the productivity of Kyle Scotnish, in terms of plankton, has been doubled by the distribution of fertilizers.

This paper was assisted in publication by a grant from the Carnegie Trust for the Universities of Scotland.

The application of fertilizers to an enclosed sea-loch (Loch Craiglin) led to a marked increase in the density of the bottom fauna (Raymont, 1947, 1949). The rise in the bottom fauna was slow, and this was to be expected, since first a considerably increased density of plankton had to be built up, and only then would the relatively slowly reproducing bottom fauna have a chance to increase in numbers. It seemed clear also from the later work in Loch Craiglin that the beneficial effects of fertilization on the bottom fauna lasted for a considerable time after application of fertilizers had ceased.

Fishing with both a shore seine net and a small otter trawl in the summer of 1943 and the spring of 1944 showed that the native fish population was very sparse. No estimate of the size of fish population was attempted in 1944. Estimates undertaken in 1945 and 1946 will be discussed later (p. 120). Fishing in the period June to September 1945 produced small numbers of fish tabulated on p. 110, and some plaice and flounders which will be dealt with separately.

In addition there were fairly large numbers of gobies, sticklebacks, pipe fish and sand eels which, however, were not usually recorded in our catches. Shoals of young herring appeared only in the summer and autumn of 1945.