Contrary to expectations, an international team of scientists has shown that the diversity of sharks and rays has steadily declined since its peak roughly 45 million years ago, highlighting fresh concerns for today’s threatened species.

Led by researchers at the University of Vienna, the study examined fossil records alongside environmental data, showing that, while the mass extinction event 66 million years ago had a limited impact on sharks and rays, the largest radiation occurred in the Eocene and has been followed by a sustained decline. This finding challenges earlier assumptions that cartilaginous fish diversity was stable or increasing in modern times. 

Key findings and implications 

By analysing genus-level occurrence data spanning the Cenozoic Era, the authors identified two major faunal turnover events during the Miocene. Their modelling identified shallow, heterogeneous coastal habitats as critical drivers of diversity—but these very habitats are under severe human pressure today, from development, fishing, warming seas and acidification. 

The study emphasises that current threats—such as overfishing, habitat loss and rapid climate change—pose a more urgent risk because sharks and rays no longer have the geological timescales needed to adapt. More than one-third of modern species are already assessed as threatened.

What this means for diving and conservation 

For the dive community, the findings reinforce the vulnerability of even top predator groups. Sharks and rays, often perceived as resilient, are shown to be subject to long-term decline when habitat integrity, prey availability and environmental stability degrade. The research invites us to treat each sighting, not as reassurance, but as part of a system under pressure.

From a conservation-heritage perspective, the work underscores the importance of protecting shallow coastal zones—seagrass meadows, coral reefs, and mangroves—where elasmobranchs once diversified. For technical divers, marine researchers and heritage practitioners, the message is clear: exploration and monitoring must be coupled with habitat protection, data collection, and long-term planning.

Take-away message 

The story of shark and ray diversity is not one of growth, but of gradual decline. While the fossil record confirms a golden age millions of years ago, today’s species operate in a shrinking ecological niche. Conservation efforts must therefore treat the past not as a benchmark of success, but as a warning of what is being lost.