Population size and structure of grey nurse shark off east and west Australia

About the report

• The grey nurse shark off the east coast of Australia is listed as critically endangered and is genetically differentiated from the nearest conspecific population off west Australia
• Genetic diversity was assessed in these two populations using six newly developed microsatellite markers
• 87 DNA samples were examined, 63 from east Australia and 24 from west Australia
• Allelic richness, a standardised measure of genetic diversity, was significantly greater in the west Australian population
• Our modelling demonstrates that within populations, connectivity among aggregation sites substantially minimises the rate at which genetic variation is lost.
• Using a suite of analyses we show that there is a high degree of differentiation between the two populations and no evidence of differentiation within either of these populations, implying high levels of dispersal among aggregation sites.
• A measure of contemporary effective population size (Ne) was calculated for the east Australian population, small sample sizes limited our ability to reliably estimate Ne for the west Australian population. Effective population sizes were estimated to be 126.31 (95% CL = 67.73- 474.11) for the east Australian population.
• Models indicate that genetic variation in the east Australian population will be mildly eroded across generations with a population size maintained at 126 breeding individuals, even with high levels of dispersal among aggregation sites.
• The current east Australian effective population size appears to be less than optimal for long-term persistence.