No abstract

The management of endangered species is complicated in the marine environment 26 owing to difficulties to directly access, track and monitor in situ. Population genetics 27 provide a genuine alternative to estimate population size and inbreeding using non-28 lethal procedures. The long-snouted seahorse, Hippocampus guttulatus, is facing 29 multiple threats such as human disturbance or by-catch, and has been listed in the red 30 list of IUCN. One large population is found in the Thau lagoon, in the south of 31 France. A recent study has shown this population belongs to a genetic lineage only 32 found in Mediterranean lagoons that can be considered as an Evolutionarily 33 Significant Unit (ESU) and should be managed with dedicated conservation 34 strategies. In the present study, we used genetic analysis of temporal samples to 35 estimate the effective population size of the Thau population and correlations between 36 individual multilocus heterozygosity and fitness traits to investigate the possible 37 expression of inbreeding depression in the wild. Non-invasive sampling of 172 38 seahorses for which profiles were pictured and biometric data recorded were 39 genotyped using 291 informative SNPs. Genetic diversity remained stable over a 7-40 year time interval. In addition, very low levels of close relatedness and inbreeding 41 were observed, with only a single pair of related individuals in 2008 and two inbreds 42 in 2013. We did not detect departure from identity equilibrium. The effective 43 population size was estimated to be Ne= 2742 (~40 reproductive seahorses per km²), 44 larger than previously thought. No correlation was observed between heterozygosity 45 and fluctuating asymmetry or other morphometric traits, suggesting a population with 46 low variance in inbreeding. Together these results suggest this population does not 47 meet conventional genetic criteria of an endangered population, as the population 48 seems sufficiently large to avoid inbreeding and its detrimental effects. This study 49 paves the way for the genetic monitoring of this recently discovered ESU of a species 50 with patrimonial and conservation concerns.