Future of the research
We plan to carry on the fundamental parts of our research in the long term: we need to get information about phenotype and breeding success for a large number of years to get the large samples required for a detailed analysis of the action of selection on individual life histories. Sea Lion Island was selected at the beginning of the study because it shelters a small and localized population of elephant seals, and this represent an ideal situation to collect high resolution data about ecology and behaviour of individual animals. Our field work fully confirmed these expectations. Now, our first goal is to carry on the routine work of marking, censusing and observation that permits us to collect detailed information about breeding of marked individuals. On the other side, we plan to experiment and develop new techniques that should improve our understanding of the population and of individual reproduction.
We started our study of acoustic communication by analyzing aggressive vocalizations of males: these sounds are very stereotyped, and hence easy to study, and have an evident functional relationship with male competition for breeding opportunities. Now, we wish to expand the scope of this part of the project by studying in a very detaild manner the complete repertoire of the species. In particular, we wish to improve our knowledge of ontogeny of acoustic communication, and we wish to examine the role of vocal signals in the establisment and mantainance of mother- pup bond. With regards to male communication, we see two promising areas of research. The first one is the relationship between acoustic similarity and genetic kinship. It's almost clear that aggressive vocalizations of different males present a different degree of similarity in acoustic structure (both micro and macro), that permits to classify males in a small number of vocalization kinds or categories. The genetic project carried on by Anna Fabiani at Durham University should produce quantitative indices of kinship among males, and, hence, we should be able to compare genetic kinship with acoustic similarity. The second crucial area is the study of proximate determinants of vocalizations. Male tendency to vocalize depends on his breeding status in each part of the breeding season, and this should in turn depend on hormonal control. We wish to directly relate the variation in acoustic structure of vocalizations of each male with his hormonal status, by analyzing testosterone content of saliva samples.
Breeding strategies of females
The study of breeding strategies of females requires good measures of their parental investment. An accurate measure of the post partum parental effort is the gain in weight of the pup between birth and weaning. In 1996 we started the weighing of pups and weanlings,. For pups, we used a simple canvas bag and a 500-kg digital dynamometer, held up by two people. The weanlings were weighed using a weighing bag (a cotton sheet with straps cut out to fully enfold the weanling, held up by two horizontal aluminum poles connected by steel chains and springs to a dynamometer) and the same dynamometer used for pups, held up by a half ton crane or an aluminium trypod. Due to the large variation in the interval between weaning and weighing of pups we corrected the observed weight by the weight lost between weaning and weighing, as estimated as the product of the number of days between weaning and weighing and a sex- and week-dependent correction factor ranging from 0.78 -1.02 kg lost per day. Our weighing techniques are now well developed for both pups and weanlings, but to be applied widely more field helpers are required. The next season we hope to be able to employ enough people to start a full scale weighing plan. Along with weighing operation, we carried out observation of mother-pup couples using a focal animal sampling scheme with continuous recording (Altmann, 1974) to gather data on mother and pup time budget, on frequency and length of suckling bouts, and on effect of male behaviour on lactation.
Survival of juveniles
We are now getting accurate estimates of survival rate of adult individuals, but our data about survival between weaning and start of breeding are scarce. The research team carries on field work on Sea Lion Island for the whole length of the breeding season, but not during the molt: hence, we are not able to collect data about survival of younger individuals, that haul out only during the molting season and not during the breeding. The resighting of these individuals will permit to estimate survival rates of younger age classes (yearlings, two years old males and females, juvenile males, nulliparous females), and to complete our record of individual life histories, improving our understanding of individual breeding strategies. Survival of the young individuals, and in particular survival during the first year of life, is the single most important demographic parameter of elephant seals population and a crucial phase in individual life histories. Variation in first year survival is the most relevant factor in the control of population size: hence, the proper forecasting of the status of the Sea Lion population will require an exact estimation of survival rate of yearlings. We tagged all pups born on Sea Lion Island from 1995 to 1998 and the tag loss rate in yearlings and 2 years old individuals was low. Hence what we really need is a good resighting coverage of the molt season (November-March): we already cover November, but we lack information for the rest of the molt. Each elephant seals should stay on land for molting for at least 20 days: hence with a small resighting effort, we should be able to collect very valuable data, that at the moment is almost completely lacking. Data collected in November gave us preliminary information on yearling and juvenile survival but good estimates of actual survival rate may be gathered only with a full coverage of the whole molting season.
Elephant seals in the rest of the Falklands
Currently, very few information about elephant seals distribution and breeding outside Sea Lion Island and in the rest of the Faklands is available. We collected anecdotal information from different sources and the preliminary evidence is not reassuring: Sea Lion Island seems to be the main breeding site of elephant seals in the Falklands and other sites have been almost abandoned in recent years (e.g. Elephant Point of Sounders Island). The Falklands are changing at fast pace, and the potential impact of these changes on wildlife in general, and elephant seals in particular, should be evaluated carefully. Elephant seals are a valuable resource of the Falklands, and the first way to conserve them is by improving our knowledge of their biology. One of the subsidiary target of the long term project is to complement the high resolution information available for SLI with general information for the rest of the islands. In particular: The long term demographic cycles of the population should be analyzed. Predicting the future of mammalian populations requires long time series of demographic and life history parameters: for example, the short term stability of the effective size of our seal population may be confirmed in the long term only when long time series of number of breeding females, pup mortality rate, and adult survival rate will be available. One of the goal of our long term study of this population is to obtain this kind of evidence. The distribution of breeding elephant seals should be assessed. The population of Sea Lion Island seems to represent what is left of the formerly large population of the Falkland Islands. Preliminary information from surveys of the entire Falklands coast for marine birds census, carried out at the end of the elephant seal breeding season, showed very limited signs of breeding (Mike Bingham, pers. comm. 1996; Mike Morrison & Robin Woods, pers. comm. 1998). Therefore, the future status of the Sea Lion Island population could have a significant role in the conservation of the entire Falklands population. The level of isolation of SLI population should be quantified by genetic studies.Currently, an ongoing research project is comparing the genetic structure of SLI population with South Georgia and Valdes Peninsula populations, the two main parts of the South Georgia stock, which comprises about one third of the world wide elephant seals population. The Falklands population could provide a link between these two populations, but it appears to be almost isolated during the breeding season.