Project 0708/26

Project Title: Methods for distinguishing foraging ecotypes within and among Australian sea lion subpopulations: their importance to defining genetic population structure and assisting spatial management of fisheries.

Chief Investigators: Dr Simon Goldsworthy and Professor Steve Donnellan

The Australian sea lion was listed as a threatened species under the EPBC Act in February 2005, vulnerable in February 2008 under the National Parks and Wildlife Act (1972) South Australia and added to the IUCN Redlist in 2008.  The reproductive biology of this species poses significant challenges in understanding the mechanisms that may be important in understanding population substructuring.  Previous research has highlighted matrilineal population substructuring by adult females exhibiting one of two mutually exclusive foraging ecotypes (inshore or offshore). This project represents the first year of a three year PhD being undertaken by A Lowther to examine the role of social and genetic factors in shaping Australian sea lion population substructuring.  The project was conducted at two pairs of breeding colonies (Blefuscu and Lilliput Islands in the Nuyts Archipelago, and The Pages Islands off Kangaroo Island) involving sampling at least 60% of all pups produced in a breeding season for genetic and stable isotope material.  Pup stable isotope ratios would reflect maternal values but be enriched one trophic level due to their total dependence on maternal milk.  Foraging ecotype validation was conducted by satellite tracking a random sample of adult female Australian sea lions and examining their stable isotope ratios (δ13C and δ15N).

Three successive sampling trips were conducted at the Nuyts Archipelago during the 2007-08 breeding season resulting in 62% of all pups being sampled.  Five adult female Australian sea lions were satellite tracked at each colony to provide validation of foraging ecotype isotope ratios.  Due to the difficulty of ingress / egress at The Pages Islands and the high risk of equipment loss, a single sampling trip was conducted resulting in approximately 63% of all pups being sampled at each island and a pre-existing satellite telemetry data set was used to validate foraging ecotypes. 

A lack of a priori knowledge of foraging ecotype prevented a balanced sample of inshore and offshore tracks, with only three offshore tracks recorded at Blefuscu I. and none at Lilliput I.  Examination of pup stable isotope revealed a more complex subpopulation substructure than previously suggested, with highly significant inter-colony ecotype segregation in the Nuyts Archipelago, and an equally significant intra-colony division within each colony at the Pages Islands.

The mitochondrial DNA (mtDNA) control region (approximately 1200 base pairs in length) was targeted as a suitable gene to examine any genetic basis to population subdivision.  Sequencing was hampered by the presence of PCR inhibitors and tandem repeats in the middle of the control region.  Present analyses suggests limited alignment of mtDNA haplotype with foraging ecotype, however, the genetic variation determined from the present sequence data limits interpretation at this stage.  However, the identification of tandem repeats within the control region may provide an opportunity to develop mtDNA markers similar to microsatellites that will greatly increase the resolution of maternal population substructuring. This will become a focus of genetic analyses in the final year of this project (2010) pending further funding from the AMMC.  

The report represents the summary of the first year of a three year project.  Support has been received by the AMMC to conduct extensive stable isotope sampling throughout the range of the species, and further support has been requested to examine the fine-scale molecular genetic substructuring of the entire species.