Marine conservationists have expressed concern over the declining number of endangered sea turtle sightings along the coasts of the UK and Ireland. 

A study of the record, dating back to more than a century from 1910-2018 by the University of Exeter scientists, shows that the turtle's sightings have dropped since 2000. "The reasons for this are unclear," they said. 

"Lots of factors could affect the changing of numbers of sea turtles sighted," said Zara Botterell of the University of Exeter and Plymouth Marine Laboratory. "Climate change, prey availability and environmental disasters such as the 2010 Deepwater Horizon oil spill could all influence turtle numbers and behavior."

The record shows a dramatic increase in the turtle sightings in the 1980s and 1990s, which researchers attribute to the rising public interest in conservation activities and a better reporting mechanism. 

Of the seven different sea turtle species, six of them – green, hawksbill, kemp's ridley, leatherback, loggerhead, and the olive ridley – are found in both warm and cold water oceans in many countries. But the flatback turtles reside only in Australia, Indonesia and Southern Papua New Guinea.

In the UK and Ireland, leatherback sea turtles are regularly spotted, making up 1,683 of the 1,997 sightings since 1910. These turtles visit the country's ocean during the summer months to feast on jellyfish. 

The record shows spotting of 240 loggerheads, 61 Kemp's ridley turtles during winter months. These turtles might have been carried on currents and are stranded in cold waters. But only 11 green turtles, one hawksbill and one olive ridley sightings were found in the record. 

Most of the recorded sightings of turtles in the UK and Ireland were along western and southern coasts. Of the 1,997 turtles sighted, 143 were "bycatch" (caught accidentally) in fishing lines, nets and ropes – and the large majority of these were released alive.

But researchers claim that the sea turtle populations in the North Atlantic are mostly stable or increasing. "The apparent decrease may represent reduced reporting rather than fewer turtles in our seas," said Botterell.

"One reason for this could be that fewer fishing boats are at sea now than in the past – and fishers are the most likely people to see and report turtles," she added. 

Concerned over the depleting population of sea turtles, the International Union for Conservation of Nature (IUCN) has already declared kemp's ridley, hawksbil and green sea turtles critically endangered, seeking the intervention of the governments.

Leatherback, olive ridley, green and loggerhead turtles have been placed under the endangered list. There is not enough data available about flatback turtles.  

"We have been lucky to analyze this unique dataset that exists because Britain and Ireland are a real hotbed of engaged citizen science, said Professor Brendan Godley, who leads the Exeter Marine research group. "Members of the public report their sightings in schemes supported by conservation charities and government bodies."

(Cover: Researchers measuring a leatherback sea turtle in the UK. /Jane Newman)