The rarest seal species in the world started its population decline millennia ago, possibly due to the rise of ancient human civilisations.
Mediterranean monk seals (Monachus monachus) are exceptionally endangered. Once widespread throughout the Mediterranean Sea, Black Sea and warmer North Atlantic coastlines, there are currently only a few hundred left in disjointed populations.
Previous research has shown that these groups have low genetic variation, leaving them susceptible to disease and other threats. But it wasn鈥檛 clear precisely how these seals became so vulnerable.
Advertisement
at the Paul Sabatier University in France and his colleagues sought to answer this by delving into the animals鈥� genetics. The team collected DNA from samples of the skin, hair, faeces and bones of 383 monk seals, both from current and extinct populations. After analysing the DNA, they used models to infer the timing of past drops in the number of seals and their genetic diversity.
Surprisingly, the team didn鈥檛 see signs of population declines during major climatic disruptions 20,000 years ago, which dropped the sea level in the Mediterranean by more than 120 metres. Nor did they see much impact on genetic diversity from a mass die-off of seals at Cabo Blanco on the northwestern coast of Africa in the 1990s. More than two-thirds of a group of 350 seals perished at Cabo Blanco, the only place in the world where the animals still form a true colony.
Instead, many monk seal populations shrank to a tenth of their original size or less between 800 BC and AD 600 鈥� a period that saw the rise of civilisations and widespread seafaring in the Mediterranean basin. The researchers suspect that聽 hunting of seals by people for meat and oil could have baked diminished genetic diversity into the future of the animals. The team points to the Roman Empire鈥檚 large-scale exploitation of wildlife during this period, already known to have precipitated localised extinctions of other species.
at the University of Edinburgh in the UK, who wasn鈥檛 involved in the research, says the monk seals鈥� story of ancient decline is quite different from other pinnipeds, whose present-day genetic profiles 鈥渃an largely be explained by the commercial exploitation that occurred over a relatively constrained time period in the 18th and 19th century, and whose populations have since rebounded鈥�.
Conserving the remaining monk seals may require interbreeding the now fragmented populations, given how genetically homogeneous they have become, the researchers argue.
Reference: bioRxiv, DOI:
Sign up for Wild Wild Life, a free monthly newsletter celebrating the diversity and science of animals, plants and Earth鈥檚 other weird and wonderful inhabitants
