Unusual Loggerhead Turtle

Donegal Bay

A physically anomalous loggerhead turtle (one of the largest hard-shelled turtle species in the world) discovered in Donegal in the 19th century.

By Wian Joseph

What does the specimen look like?

The Natural History acquisition register reads:

“1890:73 Logger-head Turtle juv. (Thalassochelys caretta L.) presented by Dr J.W. Tate, Mullaghmore, Co. Sligo. Donegal Bay. Found alive on 7th April. The specimen is of interest in that 4 inframarginal scutes on left side & 3 on right, 22.ix.1965. Length of shell - 8 1/4 ins (210 mm). Width - 6 3/4 ins (173 mm). do incl. head -10 ½ ins (268 mm) ”

The specimen consists of the whole animal, which has been preserved by drying and is now housed in a cardboard storage container. It is approximately 268mm long and 173mm wide and still maintains much of its original pattern and colouration.

How did it end up in the Museum?

This animal was found stranded on Donegal Bay on the 7th April 1890, but subsequently died and was donated to the museum collection on 11th April 1890 by Dr M.J. Tate. This particular specimen is of scientific interest, as it is representative of an anatomical anomaly and an ecological phenomenon.

What makes it so unusual?

Loggerhead turtles are the largest, hard shelled turtle species in the world. The shell is made up of the carapace (top half) and plastron (bottom half), which are covered in keratin plates called scutes. The carapace and plastron are held together by special plates called inframarginal scutes, which are located between the front and back flippers of the turtle. Loggerhead turtles typically have 3 pairs of inframarginal scutes, however this specimen has one extra scute on its left side; this is an anatomical anomaly.

Why was this turtle stranded?

Loggerhead turtles around Irish coasts are mostly brought here by a warm ocean current called the Gulf Stream that has its origins in the warm waters of the Caribbean. Loggerhead turtles are exothermic, depending on their surrounding water temperature to regulate their body temperature. When there is a sudden sustained drop in the water temperature turtles can experience cold-stunning. Cold-stunning similar to hypothermia in humans, symptoms include lethargy, reduced feeding and diving behaviour, prolonged surface floating, paralysis, stranding and death. Younger turtles are more susceptible to cold-stunning due to their smaller size, compared with an adult. Many juvenile turtles, like this museum specimen, are found stranded after a cold-stunning event.

Is it an important part of our collection?

For scientists specimens such as this provide a valuable insight into the effects of water temperature changes on local ecology and it also help to map out effects of water temperature changes over time.

Learn More...

This specimen is part of the Museum’s scientific research-collections, and is not accessible to the public. However, in the Irish Fauna exhibition on the ground floor of the National Museum of Ireland - Natural History you can observe a mounted example of a loggerhead turtle, which was also found stranded on the Irish coast (Co. Galway).

• Spotila, James R. (2004) Sea Turtles, a complete guide to their biology, behaviour and conservation, Baltimore: The Johns Hopkins University Press and Oakwood Arts.