Sea Lion Project sea lions

Research Focus

The consequences of life-history decisions of individuals on reproductive success have only rarely been documented in sufficient detail to allow understanding phenomena at the level of population dynamics. This study proposes to analyse the consequences of life history decisions of male and female individuals under environmental uncertainty and to model the demographic consequences of individual decisions in a large mammal, the Galápagos sea lion (Zalophus wollebaeki). Due to its island tameness the population offers a unique opportunity to determine how male and female reproductive strategies, juvenile development, and juvenile and adult mortality rates together generate the population dynamics of a large marine predator. This is particularly interesting since Galápagos sea lions live in an environment characterized by high variance in food abundance due to frequent disturbances of the oceanic regime by El Niño, which creates a major decline in food resources. El Niños appear to depress juvenile growth, lower female fecundity and may lead to large increases of mortality in juveniles and adults. Effects appear to vary with sex and age class, correlated with reproductive strategy and diving ability. By modelling the effect of individual life history decisions on population dynamics, the study will bridge the gap between life history and population dynamics. Moreover, it will show to what extent life history decisions allow adaptation to a highly variable environment or whether they must be understood more parsimoniously as passive tracking of environmental changes.

Individual Projects

Zalophus wollebaeki independence

Transition to independence
--> Paolo Piedrahita

Zalophus wollebaeki network

Social networks
--> Kristine Meise

Zalophus wollebaeki swimming

Ontogeny of the diving behaviour of juveniles
--> Jana Jeglinski

Zalophus wollebaeki males

Mating strategies and reproductive success of males
--> Dr. Ulrich Pörschmann

Zalophus wollebaeki trio

Life history decisions and reproductive success of females
--> Dr. Birte Müller

Zalophus wollebaeki trio

Genetic and social structure of colonies
--> Dr. Jochen Wolf


Help us collecting data

If you want to contribute to our project and are in Galápagos, you can do so by keeping your eyes open for sea lions with coloured flipper tags. If you see one, please note the place and date where you saw it, the colour of the tag and the number printed on it. You can send the information either to, or just to any of our project's team members. If you could provide a picture of the tag would be best.

Every small bit of information is usefull and can help us understand the distribution and the movements between different colonies of the sea lions.

Since the printed number on the tags may fade away, we punch holes in them corresponding to the number.




Jeglinski, J.W.E., Mueller, B., Pörschmann, U. and Trillmich, F. (2010): Field-Based Age Estimation of Juvenile Galapagos Sea Lions (Zalophus wollebaeki) Using Morphometric Measurements. Aquatic Mammals 36 (3): 262-269.

Mueller, B., Pörschmann, U., Wolf, J.B.W., Trillmich, F. (2010): Growth under uncertainty: the influence of marine variability on early development of Galapagos sea lions. Marine Mammal Science 26, DOI: 10.1111/j.1748-7692.2010.00404.x.

Pörschmann, U., Trillmich, F., Mueller, B., Wolf, J.B.W. (2010): Male reproductive success and its behavioural correlates in a polygynous mammal, the Galápagos sea lion (Zalophus wollebaeki). Molecular Ecology 19: 2574-2586.


Kunc H, Wolf JBW (2008) Seasonal changes of vocal rates and their relation to territorial status in male Galápagos sea lions (Zalophus wollebaeki). Ethology 114: 381-388.

Trillmich F, Rea L, Castellini M, Wolf JBW (2008). Age-related changes in hematocrit in the Galápagos sea lion (Zalophus wollebaeki) and the Weddell seal (Leptonychotes weddellii). Mar Mamm Sci.v 24, 303-314.

Trillmich F & Wolf JBW (2008) Parent-offspring and sibling conflict in Galápagos fur seals and sea lions. Behav Ecol Sociobiol 62:363-375.

Wolf JBW, Harrod C, Brunner S, Salazar S, Trillmich F, Tautz D (2008) Tracing early stages of species differentiation: ecological, morphological and genetic divergence of Galápagos sea lion populations. BMC Evol Biol 8:150.

Wolf JBW, Trillmich F (2008). Kin in space. Social viscosity in a spatially and genetically sub-structured network. Proc R Soc Lond B 275, 2063-2069.


Wolf JBW, Mawdsley D, Trillmich F, James R (2007) Social structure in a colonial mammal: Unravelling hidden structural layers and their foundations by network analysis. Anim Behav 74, 1293-1302.

Wolf JBW, Tautz D, Trillmich F (2007) Galápagos and Californian sea lions are separate species: genetic analysis of the genus Zalophus and its implications for conservation management. Front Zool 4:20: 1-13.

Wolf JBW, Trillmich F (2007) Beyond habitat requirements: individual fine-scale site fidelity in a colony of the Galapagos sea lion (Zalophus wollebaeki) creates conditions for social structuring. Oecologia 152, 553-567.


Wolf JBW, Kauermann G, Trillmich F (2005) Males in the shade: habitat use and sexual segregation in the Galápagos sea lion (Zalophus californianus wollebaeki). Behav Ecol Sociobiol 59, 293-302.


Deutsche Forschungs Gemeinschaft  


Charles Darwin Foundation Galápagos National Park


Ortlieb - Waterproof Zarges
Panasonic - Toughbook Huntsman

Sie befinden sich hier: Universität Bielefeld > Fakultät für Biologie > Lehrstuhl Verhaltensforschung > Fritz Trillmich >