Controversial Molecular Signatures of Past Demography in the Totoaba: A Critically Endangered Species with High mtDNA Diversity and a Large Effective Population Size

Even when records of historical abundance for most fish stocks are seldom known, there is abundant empirical evidence of depletion by over-fishing or anthropogenic habitat alteration in many of them. Severe reductions in population size can lead to a rapid loss of genetic diversity, thus compromising adaptive potential and increasing the risk of extinction. As a consequence, conservation biologists had been increasingly using analytical tools, particularly some emerging Bayesian approaches, for reconstructing historical population dynamics from genetic data. Totoaba was the target of a profitable commercial fishery which apparently collapsed due to overfishing and habitat deterioration. Using mtDNA sequence data obtained from 792 seized swim-bladders, both classic and Bayesian approaches confirmed previous controversial data showing unexpected high genetic diversity and the lack of evidence for a strong bottleneck in the totoaba population. Moreover, derivations of posterior parameter estimates suggest a sudden and recent demographic expansion about 1,650 years before present and a larger effective population size than previously estimated. Even when the above scenario is remarkably inconsistent with the largely assumed critically endangered status of the species, there are concerns on the magnitude and the impact of poaching on adults and juvenile bycatch on population numbers.