Why do we find young sea turtles on cold, northern beaches?

Young sea turtles are regularly found dead or dying on the shores of the UK. Researchers may have found out why.

liten havskilpadde på en strand
Sea turtles are very susceptible to climate change, as they are highly affected by changes in weather conditions and ocean currents. Foto: Rawpixel.com
Portrettbilde av Bludd, Ellen Kathrine
Bludd, Ellen Kathrine ellen.kathrine.bludd@uit.no Kommunikasjonsrådgiver
Portrettbilde av Kettemer, Lisa Elena
Kettemer, Lisa Elena lisa.e.kettemer@uit.no Stipendiat
Publisert: 16.08.22 15:00 Oppdatert: 23.08.22 10:58
Opprinnelig publisert i sciencenorway.no
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Sea turtles are unexpected visitors in northern Europe, as the waters here are generally too cold. While there are only a few turtles in most years, in some years, beach-goers in the United Kingdom have reported up to 26 small turtles. People wonder where these unexpected visitors come from, are worried about why they are sick or dead, and what may cause the high number of strandings in certain years.

We have tried to find the answer. Due to the efforts of the public in reporting these stranded turtles, we were able to analyze which environmental conditions may cause these incidents. The research was conducted at the GEOMAR Helmholtz Center for Ocean Research in Kiel, Germany, and UiT The Arctic University of Norway in Tromsø.

svømmende skilpadde
Newly hatched sea turtles use ocean currents to reach productive and warm ocean regions where they can feed and grow. Foto: Rebecca Scott

Too small to track

Sea turtles are at risk from climate change impacts, and it is important to understand how they survive in the ocean at a young age. Because they are too small to track and find in the ocean, simulations can help to better understand what is often referred to as “the lost years” - a developmental phase that sea turtles spend in the ocean, away from human eyes.

Using an ocean simulation model allowed us to track “virtual turtles” during this elusive period.

Use ocean for transportation

We used the simulation model to show that ocean currents can transport young turtles from their nesting beaches in the USA across the Atlantic.

Young turtles can swim directly after reaching the ocean when they are only a few centimeters large, but they rely on ocean currents to transport them over long distances in the ocean, usually to warm waters. But sometimes they end up in lethally cold northern European waters.

svømmende skilpadde
Young turtles ride ocean currents and influence their path by swimming actively, but sometimes they get swept away into colder waters. Foto: Rebecca Scott

Stormy weather

During years when the North Atlantic Oscillation (NAO), an indicator for the "mode" of the climate, was high, more turtles were reported in the UK. The NAO describes environmental conditions, such as ocean currents and the occurrence of storms, which may be responsible for bringing many turtles to UK beaches.

In addition, near-shore weather may also influence the number of reports, for example in years with more nice weather days, more people on beaches are more likely to find the stranded turtles.

skilpadde på et isopor fat
Rod Penrose transfers a deceased Kemp’s Ridley turtle to the Zoological Society of London for further analysis. Foto: Lin Gander

Susceptible to change

An increased understanding of the sea turtle lost years is critical for conservation efforts because the population dynamics of marine species with dispersive juvenile stages can be altered by survival rates of early life stages. These organisms are very susceptible to variations in climatic and oceanic factors.

With climate change causing atmospheric and oceanic conditions to change, it is becoming ever more important to understand how organisms with drifting life stages will be affected by future environmental conditions.

Read the scientific publication here: Oceanic drivers of juvenile sea turtle strandings in the UK

Opprinnelig publisert i sciencenorway.no
Bludd, Ellen Kathrine ellen.kathrine.bludd@uit.no Kommunikasjonsrådgiver
Kettemer, Lisa Elena lisa.e.kettemer@uit.no Stipendiat
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