Seals are an impressive example among mammals to have made the step back into aequous habitat. Nonetheless they are still bound to breed on land. During the reproductive period, they form large colonies with highly competitive polygynous mating systems, where a great number of females is temporarily monopolized by a dominant male. Apart from the social structure imposed by the mating system itself, little is known about internal social structuring within such colonies. Little effort has been made to investigate the behavioural interactions of individual females towards each other, although observations suggest that the interaction patterns differ widely. Whether friendly or antagonistic behaviour is displayed may depend on the respective partner an interaction takes place with. It might as well be due to physiological traits, such as reproductive status. It could be shown for captive Californian sea lions (Zalophus californianus), that kinship played a major role in this. Many more "friendly" interactions occurred between closely related individuals, i.e. mother, daughter, granddaughter. This data suggest matrilinear organization rather than structuring based on early relationships ("friendship"). Supporting the possibility of longterm relation among matrilinear kin, research data on the Galápagos fur seal (Arctocephalus galapagoensis) and on the Northern fur seal (Callorhinus ursinus) showed, that females remember the voice of their offspring for many years.

In my PhD thesis I will try to assess the importance of matrilines as one possible structuring factor, determining social interaction patterns among individuals in Galápagos sea lion colonies (Zalophus wollebaeki). Such relationships are almost impossible to study in the much more crowded colonies of most species of sea lions elsewhere. The study will be conducted over three years including three visits on Caamaño, an uninhabited islet of the Galápagos archipel. The very special situation of sparsely populated colonies and island tameness in Galápagos sea lions offers a unique opportunity to study social behaviour of sea lions in detail. Data gained from behavioural observations will be related to genetic evidence of kinship proximity, which will be estimated by the use of microsatellites, highly polymorphic genetic markers. The study will focus on females, since specific bonds among males are unlikely, since according to present knowledge they seem to be the dispersing sex. Internal structures along kinship lines are of great importance for two main reasons:

• If individuals of matrilines maintain special longterm relationships, this might influence reproductive success of females and contribute to patterns of geneflow within the population and to population structuring.
• It would show that sea lions are social in a true sense to a much higher extent than anybody would have expected. Finding matriliear or "friendship"-like relationships in such a colony would prove that pinniped carnivors are capable of much more differentiated social behaviour than generally assumed.

Apart from behavioural inflictions based on genetic proximity, microsatellite data will contribute to elucidate population biology traits of the Galápagos sea lion. Comparisons between populations of different Galápagos islands and populations of the Californian sea lion (Zalophus californianus) will help to estimate genetic divergence, recent geneflow, amount of inbreeding and systematic status of the Galápagos sea lion.