A range of small, long-life ultrasonic fish tags is described and their use illustrated with an improved system of fixed hydrophone tracking stations. A boat-mounted hydrophone system giving bearing and range estimations for use in open-water fish tracking is described together with a portable handheld unit for simple location of tagged fish in rivers, etc. Typical results based on intensive use of these systems are given.

Life histories and production of the five common species of Tanypodinae (Pentaneura monilis, Procladius simplicistilus, P. crassinervis, P. choreus and Psilotanypus rufovittatus) in the mud at Loch Leven were measured from March 1971 to March 1972. The methods used to identify each species of larva are described. All were univoltine except Pentaneura monilis which had two generations per year, but the seasonal patterns of the life cycles were different. The average density of third and fourth instar Tanypodinae was 3100/m2 and densities of individual species exceeded 2500/m2 for short periods in Procladius crassinervis and P. choreus. Net annual dry weight production by this subfamily was 2·6 g/m2(57 kJ/m2), with individual species ranging from 1·1 g/m2 (P. crassinervis) to 0·16 g/m2 (Pentaneura monilis). These results are discussed briefly and compared with production estimates for other zoobenthos.

The micro-organisms in rumen samples from Red deer, hill sheep and reindeer grazing their natural pastures in the Scottish Highlands were examined at different seasons over a number of years. The total counts of bacteria and protozoa varied with the season, and were lowest in winter when fermentative activity was also at its lowest.

As is usual in roughage-fed ruminants, viable counts were only a very small proportion of the total counts. The reindeer rumens had the highest concentrations of bacteria.

There were no consistent differences in the types of bacteria between seasons, but although there were no bacteria peculiar to any animal species the balance of predominant types varied between the species. The principal types of bacteria were similar to those found in domesticated ruminants. The numbers of protozoa in the Red deer were higher than those in the sheep, and the concentrations in reindeer were higher than those generally reported for domesticated cattle or sheep. A number of species of protozoa were found in each animal and the predominant species differed in the different animals.

Red deer, sheep and reindeer grazing on their normal hill ranges were examined at intervals over a period of four years. Samples from the digestive tract were taken at different seasons and processed in the field. The Red deer and reindeer were killed before samples were taken; rumen samples from the sheep were taken by stomach tube, but a number of animals were also killed at different seasons to correlate stomach tube and whole rumen samples. The animals sampled were representative of the general condition of the herds. Examinations were made for parasites and any pathological conditions. In most instances parasitic infections were slight. Apparent seasonal changes were found in the compositions of the diets. The Red deer and sheep ate principally heather and grass, the proportion of heather increasing in the winter. The reindeer ate mainly grass in the summer, with lichens and grass forming the winter diet, and these animals seemed to have a higher nutritional status in the winter than did the other two species. The weights of the animals and of their rumen contents, the concentrations of rumen ammonia and volatile fatty acid, and the rates at which different dietary components were fermented are recorded. Rumen fermentation was low in winter and the diets were generally inadequate for the animals. A lack of nitrogen seemed to be a major factor.

Some data on caecal contents are also given.