Statistical distributions like the negative binomial distribution are commonly used to describe aggregation patterns in animals. However, recently it has been suggested that truncated power laws (TPLs) may also be used for this kind of analysis. A TPL consists of two power functions separated by a cut‐off size (C*). The cut‐off size and the slope of power function one (β1) for the smallest group sizes have been suggested to have a biological explanatory value. We applied TPLs to aggregation data of tephritid seed predators on a composite plant, aphids on willows and grey seals on a haulout site. β1 varied between 0.60 and and −0.72, which is higher than predicted. In addition, resource distribution and animal density influenced β1 and C*. This indicates that environmental dimensionality suggested to affect β1 is masked by ecological factors. We conclude that TPLs are useful due to their simplicity and, in comparison with traditional methods, provide additional biologically relevant information. Truncated power laws can therefore prove to be useful in studies of animal behaviour and population dynamics.

We investigated habitat selection by grey seals, Halichoerus grypus, around haulouts in the Baltic Sea. Home ranges (95% fixed kernel) varied in size from 1088 to 6400 km2. Observed habitat use was tested against the circular home range predicted from a simple central-place model. The overlap between the home ranges predicted by this simple model and actually exhibited by the seals was <70% for 9 of 11 seals. Furthermore, the depth distributions of the utilised areas were significantly different from that available in the circular home range for all 11 seals. Seals selected depths of 11-40 m and avoided areas >51 m deep. Ten of the 11 seals used areas within a 50-km radius around the haulout site for more than 75% of the time. Thus, in spite of their mobility and the availability of many islands, seals usually remained in the vicinity of a specific haulout site for extended periods. The seals did not use the habitat around the haulout site as predicted by the simple central-place model, but selected habitat according to bathymetric characteristics (e.g., water depth). Detection of these relatively small but heavily used home ranges around haulout sites may be of assistance in management plans in order to reduce the growing number of seal-fisheries conflicts.

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The effects of size and previous sexual maturity on downstream migration in two‐summer‐old Baltic salmon were studied during their normal seaward migratory period in spring. We used an automatic PIT (Passive Integrated Transponder) tag monitoring system for individual recognition of tagged fish. Size affected the probability of migration among both previously immature and previously mature males while there was no such relationship among females. Nearly all females and 63.6% of the previously immature males migrated during the smolting period, while only 24.5% of the previously mature males did. In migrating fish the individual activity level increased from almost zero in May to about 450 antenna passages per day in mid June, coinciding with a pronounced increase in ambient water temperature. During the period of increasing activity in early June the fish changed from night activity to day activity and finally activity all day and night. The fish moved downstream in schools but no specific school size dominated. This paper demonstrates the strong effect of body size and previous sexual maturity on the probability of migration.

The haulout pattern of seals, i.e. the distribution of the time they spend on shore or on ice, may be influenced by a large number of extrinsic factors such as season, time of day and weather, as well as factors related to the animal's internal state. In this study we used a time‐lapse video system at a haulout site, and satellite relay data loggers attached to 11 individual seals to monitor haulout pattern of grey seals Halichoerus grypus in the Baltic Sea during summer and early winter from 1989 through 1996. Time of day had the greatest influence on haulout patterns with the maximum numbers of seals ashore at night. Season and habitat specific characteristics also had important effects on haulout pattern. We suggest that diel changes in prey behaviour and distribution account for the nocturnal haulout pattern observed. The size of the population of grey seals in the Baltic Sea has been estimated by the number of seals ashore. Our results demonstrate the possibility of improving future estimates using a correction based on time of day.