Creature Feature - The Thornback Ray
Creature Feature Week 4
This week, diver, freediver and snorkeller Anya is introducing us to another underwater resident: "I am lucky enough to spend my working days on and under the water and get to spend time in a wonderful environment. I'd like to introduce you to a majestic and elegant creature that I will never get tired of seeing - the Thornback Ray – "Raja clavate".
We have several different rays in our waters, but the Thornback is the most often encountered by divers and fisherman. This nocturnal hunter spends the day buried in the sand and has evolved over time so when buried, as they prefer, their breathing holes called spiracles are located behind the eyes and above the sand. These also help with a developed sense of smell that they use to hunt prey, preferring to eat crustacea, worms, molluscs, and echinoderms.
They have a very distinctive flat diamond shaped body with tail. Juveniles have small black spots which change as they grow to form a pattern across the light brown or grey body. The patterning on a thornback will extend all the way to the edges of its wings, so is a great way to tell it from other species. The common name comes from the large thorn like projections across its back and along the tail, scattered in young rays but which fully develop into lines as an adult that extend down the tail.
Like all sharks and rays, they start life in an egg case called a Mermaids Purse. Each purse contains just one embryo which develops in the case for between 4-6 months. After that time, a perfect miniature ray will hatch out to begin life. They may start small but the largest ever recorded weighed an immense 18kg. Living for up to 12 years, most reach about a metre across. One adult is likely to lay only 140 eggs a year and males do not reach maturity until 8 years old, that is potentially as few as 560 rays that he will sire in a lifetime.
Photos: Cat Briggs / Anthony Mills