The use of consistent baseline numbers for species distributions and population size is of uttermost importance for the definition of sustainable fishing effort. The conventional approach for the estimation of pre-exploitation abundance of species consists in summarizing catch record from logbooks fishery catch data and add those to estimates of current abundance, based in several methods (capture recapture, sightings, census, sampling). However, the time span for which this data is available is incredibly short, without many records from before 1970 and none at all from before 1950. Furthermore, sometimes these numbers are notoriously inaccurate, to hide overfishing of some species. Genomics can assist the fishing industry to maintain productive and sustainable harvests in matters like species identification (both fisheries and by-catches), stock structure, detection of pathogens and invasive species, assessing product provenance, definition of population units and stock assessments, measuring genetic diversity of populations and, if historical samples are used, looking at evolutionary responses to fishing and assessing species genetic diversity prior to overfishing. This is what we aim with this research proposal, to use historical sardine and Atlantic horse and chub mackerel specimens, to look at genetic diversity on two different time points, pre and post-industrial exploitation in an attempt to implement a hindcasting to forecast strategy which will improve our understanding of fisheries and help predict future population fluctuations. Fish bones are very common in the archaeological record, however their use in archaeogenomic studies has been minimal, probably due to its fragmentary nature which makes it difficult to identify species or even genus. Their potential is however enormous, as their assemblies open a new window to understanding subsistence economy, culture, and the diet of past peoples. Here we chose to concentrate on the European sardine (Sardina pilchardus), the Atlantic chub mackerel (Scomber colias) and the Atlantic horse mackerel (Trachurus trachurus), given their huge economic value in Iberia and the unprecedented data available on modern populations distributed throughout the species range. Before the relatively well documented exploitation of the past decades, these fish were already a very important component of human diet. They were used by the Romans, in the making of fish sauces, like garum or liquamen. These species have large effective population sizes, schooling behaviour and great dispersal capabilities, and several genetic markers show low levels of genetic differentiation. However, our recent study based on 103 genomes from across the sardine range clearly show at least three genetic clusters; confirming that high dispersal capability in marine environment does not necessarily translate into high levels of gene flow and lack of structure. In this project we will use aDNA to uncover the pre-exploitation diversity levels of pelagic fish populations. A pilot study done on sardine bones from Adro Vello, Galicia, confirms the feasibility of the research proposal, as we were able to get endogenous DNA from most processed specimens. These historical samples will allow us to open a window into the past, where species were not yet overexploited, granting us a baseline data on populations both in terms of effective population size and in terms of genetic diversity. We hypothesize that genetic diversity was lost over time in response to the unsustainable fishing practices of the last century, so assessing how much diversity was lost in the past millennium and establishing a baseline for these species before commercial fishing started will give us a more accurate perspective of pristine populations, invaluable information for stock delimitation and management and definition of fishing effort in the different Food and Agricultural Organization (FAO) fishing areas.