The patterns of movements of indigenous and displaced trout (Salmo trutta) in a small loch were obtained by ultrasonic tracking techniques. Comparisons of these were made by developing stochastic simulations of their movements based on an analysis of the frequency distributions of step lengths, angles of turn and the percentage time spent actively swimming.

The dispersal and escape of displaced fish from an unfamiliar area of the loch can be explained principally in terms of random turning. Nose plugging appears to influence the distribution of the angles of turn without significantly altering the time taken to escape and return home.

Indigenous trout show a strong preference for turns of 180°, indicating a tendency to turn in their tracks. Although a simulation of the indigenous fish shows slower dispersion than displaced fish, it is insufficient to explain the containment of movement within a home range. It is probable that successive steps are not independent and there may be some association between step lengths and subsequent angles of turn. The implications of their autocorrelation are discussed.

Estimates of the rates of secondary production by the individual macrofaunal invertebrates of two Indian beaches are presented and these are combined to give an estimate of the energy flow through the macrobenthos of the two beaches. The production by individual species and by the macrofauna as a whole is compared with that of other tropical, and of temperate beaches, and it is concluded that a similar biomass in the tropical beaches produces a rate of turnover of biomass some ten times that of the temperate beaches. Values of production to biomass ratios (P/B) and of elimination to biomass ratios (E/B) for the invertebrates of sandy substrata in various geographical areas are reviewed and the use of these ratios in comparisons of productivity, and their relationship to mortality and longevity are discussed.

Investigation of a temperate and tropical beach has shown that, based on chlorophyll a analyses, an epipsammic diatom population present in the temperate beach is absent in the tropical beach. Comparison of community respiration rates for the two beach populations excluding macrofaunal respiration shows that the tropical beach rates (which were constant over the period January-March) were about 9 times the winter rates of the temperate beach and about twice the summer rates. Annual microbial production is estimated at 15 gC/m2 for the temperate beach and 72 gC/m2 for the tropical beach. The greatly increased rate of production in the tropical beach was considered to be a function of increased water flow into that beach. In comparison, meiofauna and macrofauna biomass are less in the tropical beach and their respective production likely to be at most no more than in the temperate beach. It is proposed from experimental studies that the failure of animal populations fully to utilise microbial production in sandy beaches is due to the relative degree of exposure stripping significant quantities of microbial growth from this system. This proposal is discussed as a means of explaining mechanisms of control of animal production in sandy beaches.