Novel insights into the reproductive strategies of wild Chinese sturgeon (Acipenser sinensis) populations based on the kinship analysis

Understanding the reproductive strategy of an organism is important in conservation ecology as it directly affects the population performance under changing environmental conditions. Chinese sturgeon (Acipenser sinensis) are the largest anadromous fish in the Yangtze River, China. Currently, the species has only one spawning ground and has failed to spawn in recent years, leading it to the brink of extinction. To develop effective conservation measures, a further understanding of its reproductive strategy is needed. In our study, we conducted kinship analyses by using mitochondrial and microsatellite DNA data from 216 wild juveniles collected over nine years (2006-2013, 2015) to understand the mating system, breeding interval, effective number of breeding adults, and reproductive success. The results from these analyses suggested polygynandry, with some parents contributing up to eight half-sibling juvenile genotypes. Although the spawning ground was restricted to a limited area, genetic diversity was maintained at a relatively high level (observed heterozygosity from 0.698 to 0.787 and expected heterozygosity from 0.763 to 0.787) and inbreeding coefficients in each year-class ranged from -1% to 9% (low to modest detrimental effects on offspring). A parental inference analysis revealed that Chinese sturgeon have a breeding interval of 2-6 years, indicating that it has the potential to feed, accumulate nutrition in the ocean, and then migrate back to the Yangtze River for iteroparous reproduction. The annual effective number of breeders in the Yangtze River ranged from 14 to 161 during the study period, and it decreased by 62.1% from the 2011-2014 year-classes. This sharp population decline likely contributes to the reproduction failure. However, the ratios of effective to census population size (Ne/Nc) were all larger than 0.20 after the 2010 year-class, indicating relatively even reproductive success. Based on these results, a suggested approach to protect this species is to restock parent fish to increase the reproductive stock size and optimize the discharge of the Three Gorges Dam to reduce the unsuitable hydrological conditions and rehabilitate spawning ground habitats.