Connectivity and effective population size of east Australian grey nurse sharks

Knowledge of connectivity and effective population size (Ne) can be used to evaluate the impacts of various threatening processes. Estimating total population size or connectivity through direct field observation is often difficult and genetic techniques provide an alternative approach. This study uses thousands of single nucleotide polymorphisms to investigate connectivity and Ne of the critically endangered grey nurse shark (Carcharias taurus) across 1400 km of their east Australian range. This population has suffered a severe decline in numbers over the past few decades, has low genetic diversity, and is extremely susceptible to anthropogenic mortality. Genetic connectivity among aggregation sites in east Australia was previously unknown. This study revealed that east coast grey nurse sharks are genetically and demographically connected, with the population approximating genetic panmixia. Estimates of Ne were around 400 using two different estimation methodologies. Forward simulations that used current genetic variation to estimate the effect of genetic drift in the future, revealed that maintaining an Ne of 400 will lead to a loss of genetic diversity over the next 50 generations. This highlights the importance in effective cross-jurisdictional management of this critically endangered population of grey nurse sharks.