Sara Maxwell and Jana Jeglinski at Fernandina, Galapagos Islands--Greetings from Galapagos!  I am here with Jana Jeglinski and her team to tag Galapagos fur seals and Galapagos sea lions on Fernandina and Floreana Islands.  Right now, I will give you a bit of background about the project and tomorrow I will follow up with our activities here in Puerto Ayora where we are preparing to head in the field.  Hasta manana!

Ontogeny of foraging and inter-specific competition

Galapagos sea lions show slight genetic and morphologic differences between the western part (Fernandina and western Isabela) and the central part of the archipelago. The habitats in these two areas differ largely: In the west, the sea floor breaks off forming a steep cliff and the upwelling of the cold, nutrient rich waters of the Cromwell undercurrent creates nutrient rich conditions and a very productive habitat. Many animals, like the Galapagos penguin and the flightless cormorant, can be found mostly in the productive west, where food is plentiful. The population of the Galapagos fur seal, Arctocephalus galapagoenis, the only other pinniped species constantly living in the Galapagos archipelago, is concentrated in the west, competing with Galapagos sea lions for food and space. Contrastingly, the central archipelago sits on a seafloor plateau of about 200m depth, the waters are warmer and the conditions are less productive. Here, sea lions do not compete with fur seals.
 

The genetic and morphologic differences show that Galapagos sea lions do not mix freely within the whole archipelago: Why? A possible explanation could be that young sea lions learn their specific habitat during the learning and development of their diving and foraging skills and that this habitat specification leads to an increased site fidelity, a limited exchange between west and central archipelago, to a ecologically determined separation of the two groups of sea lions and ultimately shows a very early step in the speciation process.

Based on this background, our project investigate since September 2008  the development of the foraging and diving behaviour of Galapagos sea lions in two colonies, one situated in the western part (Cabo Douglas on Fernandina) and one situated in the central part (Loberia, Floreana). The young animals are suckled by their mothers for extended periods of up to three years, but they start diving and increasingly supplement the milk by their own foraging within this time until they are weaned.

We study the diving behaviour of pups and juvenile sea lions up to an age of two years and the diving behaviour of adult sea lion and fur seal females. A small number of animals are marked with blue (Fernandina) and green (Floreana) tags to recognize animals from the different colonies even if they haul-out somewhere else. We sample our data by deploying time-depth-recorders (TDRs) on the sea lions. Pressure, time, sea temperature and GPS locations are logged on the recorder and we download the data when we recapture the animals after about two weeks. A small VHF radio with individually different frequency, deployed with each TDR, allows us to find and recapture the sea lions. Our method is used worldwide in the research of diving behaviour, the instrument weigh only a very small percentage of the total body weight of the animals and do not disturb or harm them and their natural behaviour. Complementary to the diving study, we collect dietary information by sampling sea lion faeces and stable isotope data from their hair.

Adult female sea lions dive to a maximum of 520 m, the deepest maximum depth within the groups of sea lions worldwide. In average, the diving depth is much shallower. There is a slight difference between the two colonies: Females from Floreana dived to 91 m while females of Fernandina dived to 64 m. Also, the animals from Floreana utilise the whole area of the central platform between Floreana, Santa Cruz and Isabela, while females from Fernandina forage very close to the shore of Fernandina and within the protected “Canal de Bolivar”, hauling out in Punta Mangle, Punta Espinoza and Cabo Hammond.
The diving behaviour of adult fur seal females is completely different: Adult fur seal females, which are with 27 kg much lighter than adult sea lion females (66 – 78 kg) dive much shallower to a maximum depth of 131 m and an average depth of 32 m. We found a complete separation of foraging grounds of adult fur seal females and sea lions in Fernandina: fur seal females do not utilise the canal the Bolivar but forage far offshore the western coast of Fernandina, with a record trip distance of one female of about 230 km southwest. Six month old juvenile sea lions still completely depend on the milk of their mother: they swim rather than dive, with maximum depth of 28.5 m and an average depth of 7 m. This is very similar in both colonies.

In our coming up fieldwork, starting beginning of October, we will collect information of adult sea lion and fur seal females diving behaviour to investigate seasonal differences. The special focus is the behaviour of one year old sea lions and there is a lot of interesting questions to ask: Do they already show completely developed diving behaviour just as adult sea lion females? Where do they forage, do they compete with their mothers in the canal de Bolivar or do they swim offshore west, dive to shallower depth but compete with the fur seals?

The juvenile Galapagos sea lion is the most vulnerable age class because they only start to care for themselves, find food and hunt successfully, but they do not yet have the physiological abilities, skills and experience of adult animals. It is to date not known, when they start to dive for hunting and feeding, where they go for feeding and if that differs to the places that adult animals utilize. Any negative impact on the ecosystem of the Galapagos Islands, of natural (El Niño) or anthropogenic origin, will have its strongest effect on juvenile sea lions. The information we gather is therefore crucial for the management strategy of the Galapagos sea lion.