roman mosaic sea monster
© Gianni Dagli Orti/REX/ShutterstockA mosaic showing a 'sea monster' taken from a Roman garrison in North Africa
They are 15 metres long and weigh around 40 tonnes, but two species of whale are mysteriously absent from the Mediterranean Sea.

Now an analysis of bones found at ancient Roman fish factories shows that these whales were common there 2,000 years ago - raising the possibility of a forgotten Roman whaling industry.

The Mediterranean is home to sperm and fin whales, but no gray or right whales are found there and there are no historical records of their presence. This is a mystery to biologists.

"Why are they not there? It seems like a hole in their home range," says biologist Ana Rodrigues of the University of Montpellier, France. She was part of a team of biologists and archaeologists who analysed the DNA of a rare set of presumed whale bones found at Roman fish-processing sites in Gibraltar and northern Spain.

Missing link

Whale bones are seldom found in the archaeological record as they are usually left on beaches and washed out to sea.

The researchers found that three of these bones were from right whales and another three were from gray whales. Radiocarbon tests dated them to the Roman period, around 200AD. "This suggests that these whales were relatively common there at that time," says Rodrigues.

This work not only substantially extends the known historical range of these whales, who likely used the Mediterranean as calving grounds, but also hints at a forgotten Roman whaling industry.

Large-scale commercial whaling was thought to have been started by the Basques around 1,000AD, ultimately wiping out gray whales and right whales from the eastern North Atlantic.

But a thousand years earlier the Romans had established a massive fish-processing industry, often taking large creatures such as tuna and processing the meat in huge tanks up to 18 cubic metres in size, dotted all around the shores of the Mediterranean. Could the Romans processed whale meat too?

Roman whalers?

The written records from this time do not mention whales specifically, only "sea monsters" and "fat fish" but this new bone analysis shows that gray and right whales - both coastal species that are easier to catch than deep water species such as fin whales - were present in Roman times and that the Romans knew of their existence.

"The Romans had the means, the motives - a huge population to feed - and the opportunity for whaling," says Rodrigues, but adds that this doesn't prove that the Romans had a whaling industry.

The researchers are calling on historians to take a second look at ancient records for clues that point to a Roman whaling industry.

This research also raises the possibility that the devastating human impact on whale populations could have started a century earlier than once thought. "The impact could have started way before the Basque whalers," says Rodrigues.

Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2018.0961