SARDINOMICS: Assessing pre-exploitation baseline numbers and population dynamics of the European sardine Sardina pilchardus Walbaum, 1792 using palaeogenomics
Overfishing has been a major problem for several marine species, reducing their effective population sizes to remnants of their pristine levels. However due to the lack of accurate fishery catch data we still have a poor understanding of how these impacted their evolutionary path. One of the most impacted species was the European sardine (Sardina pilchardus), an important pelagic fish resource in Atlantic waters, with enormous economic value especially in Southern Europe and Morocco, where it is the main target of purse-seine fleets and represents a major source of income for local populations. The species is distributed from the southern Celtic Sea and the North Sea to Mauritania and Senegal, including the Azores, Madeira and the Canary Archipelagos, being also abundant in the Mediterranean. In a recent population genomic study, we have characterized 12 sardine populations encompassing the entire species range. Our results clearly show that the species’ genetic diversity can be partitioned in at least three genetic clusters. One including individuals from Azores and Madeira (two archipelagos in the Atlantic), the second encompassing Iberian populations (the centre of the sampling distribution), and the third gathering the Mediterranean and Canary Islands samples, with individuals from Iberia showing some degree of admixture. Here we will use state of the art ancient DNA techniques to look at samples that pre-date periods of intensive fishing and compare those results to the ones obtained from current populations (post exploitation). To do this we have collected specimens from three different Roman archaeological sites within the species distribution range: a) Adro Vello, Galicia, sardine bones date from the 3rd century AD and were collected from the bottom of fish salting vats; b) Tahaddart, Morocco, a population from the Mauretania Tingitana region, the first fish sample collected from this fish salting plant, that was active between the 1st- 4/5th century A.D. ; c) Lobos, Canary Islands, these samples date from the end of the first century BC and beginning of the first century AD, and were collected in a shell midden associated to a Roman purple workshop. We will extract DNA and sequence full genomes from these individuals allowing us to compare this historical pre-exploitation populations to the data obtained in our recent characterization of modern populations. Doing this will enable us to get a more accurate perspective of the effective population size and genetic diversity levels of the species prior to overfishing, invaluable information for stock delimitation and management and definition of fishing effort in the different Food and Agricultural Organization (FAO) fishing areas. This project applies an innovative way of obtaining new genomic information in a broad time frame usually not available to decision makers.