Ancient DNA SNP-panel data suggests stability in bluefin tuna genetic diversity despite centuries of fluctuating catches in the eastern Atlantic and Mediterranean.

Atlantic bluefin tuna (Thunnus thynnus; BFT) abundance was depleted in the late 20th and early 21st century due to overfishing. Historical catch records further indicate that the abundance of BFT in the Mediterranean has been fluctuating since at least the 16th century. Here we build upon previous work on ancient DNA of BFT in the Mediterranean by comparing contemporary (2009-2012) specimens with archival (1911-1926) and archaeological (2nd century BCE-15th century CE) specimens that represent population states prior to these two major periods of exploitation, respectively. We successfully genotyped and analysed 259 contemporary and 123 historical (91 archival and 32 archaeological) specimens at 92 SNP loci that were selected for their ability to differentiate contemporary populations or their association with core biological functions. We found no evidence of genetic bottlenecks, inbreeding or population restructuring between temporal sample groups that might explain what has driven catch fluctuations since the 16th century. We also detected a putative adaptive response, involving the cytoskeletal protein synemin which may be related to muscle stress. However, these results require further investigation with more extensive genome-wide data to rule out demographic changes due to overfishing, and other natural and anthropogenic factors, in addition to elucidating the adaptive drivers related to these.

Forgotten Mediterranean calving grounds of grey and North Atlantic right whales: evidence from Roman archaeological records.

Right whales (Eubalaena glacialis) were extirpated from the eastern North Atlantic by commercial whaling. Grey whales (Eschrichtius robustus) disappeared from the entire North Atlantic in still-mysterious circumstances. Here, we test the hypotheses that both species previously occurred in the Mediterranean Sea, an area not currently considered part of their historical range. We used ancient DNA barcoding and collagen fingerprinting methods to taxonomically identify a rare set of 10 presumed whale bones from Roman and pre-Roman archaeological sites in the Strait of Gibraltar region, plus an additional bone from the Asturian coast. We identified three right whales, and three grey whales, demonstrating that the ranges of both of these species historically encompassed the Gibraltar region, probably including the Mediterranean Sea as calving grounds. Our results significantly extend the known range of the Atlantic grey whale, and suggest that 2000 years ago, right and grey whales were common when compared with other whale species. The disappearance of right and grey whales from the Mediterranean region is likely to have been accompanied by broader ecosystem impacts, including the disappearance of their predators (killer whales) and a reduction in marine primary productivity. The evidence that these two coastal and highly accessible species were present along the shores of the Roman Empire raises the hypothesis that they may have formed the basis of a forgotten whaling industry.