Thorny Skate | Oceana Canada

Sharks & Rays

Thorny Skate

Amblyraja radiata

Also known as

Thorny back, thornback, maiden ray, starry ray, starry skate

Distribution

North Atlantic; Northwest Atlantic from Greenland and Hudson Bay South Carolina

Ecosystem/Habitat

Soft bottoms

Feeding Habits

Active predator

Conservation Status

Special concern/data deficient

Taxonomy

Order Rajiformes (skates & relatives); Family Rajidae (skates)

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Skates may look similar to flatfish, but they are actually much more closely related to sharks. Like sharks, a skate’s skeleton is made up of cartilage, which is softer and more flexible than bone. Skates commonly have small spines or modified scales on their bodies, but the thorny skate is aptly named because it is practically covered in these tiny thorny looking spines. They have a row of 10 to 20 large, conspicuous spines that run along their midline down their back and reaching their tail. They also have one large spine in front of and one behind each eye, large spines on each shoulder, and numerous smaller spines on their snout, pectoral fins and tail.

Thorny skates are flat and shaped like a rhomboid. They have a bluntly triangular snout and tail that is shorter than their body, with two dorsal fins at the end. Their eyes are on the dorsal (top) side of their body and their gills and mouth are on the ventral (under) side. Thorny skates are typically brown on their dorsal side with irregular dark spots, while their ventral side is white. They are rather large and can grow to just over 100 centimetres long from their snout to the tip of their tail; however their size varies greatly depending on geography.

Thorny skates, like many other sharks, skates and rays, are slow-growing, late to mature and long-lived. It is believed that thorny skates can live to be at least 28 years old, however 16 to 20 years old is more common. They reach maturity at around 11 years and are able to reproduce year-round. Females lay approximately 40 to 56 egg cases per year, which are also called “mermaid’s purses.” These egg cases are rectangular capsules with tendrils at each corner to help secure them to seaweed or rocks. Each containing a single skate embryo, or baby skate, which will feed off of the yolk sac inside the egg capsule. When the baby skate reaches about 10 to 12 centimetres long it is fully formed and will emerge from the capsule. At this stage, the young skate mainly feeds on amphipods, which are extremely small, shrimp-like crustaceans. As they grow, their diet shifts more toward other bottom-dwelling organisms including polychaete worms, decapods (such as crabs, lobster, shrimp) and fish. 

Currently, there is only one active fishery that targets thorny skates, which occurs on the Grand Banks off the southeast shore of Newfoundland. There also used to be a mixed fishery for both thorny skates and winter skates on the eastern Scotian Shelf, however that fishery was closed after both species saw great declines in abundance. Even so, thorny skates are caught as bycatch (incidental catch) in trawl, long line and gillnet fisheries across their range. Oceana Canada is campaigning to reduce bycatch in Canadian waters and help protect species like skates.

Thorny skates were assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as of Special Concern in 2012. They were assessed as such because of population declines from the 1970s to 1990s due to high fishing pressure from groundfish fisheries. Population declines leading to closure of many groundfish fisheries in the 1990s has halted the decline of thorny skates in many regions. Although many populations of are now considered stable, they are still found in low numbers compared to historical averages. Bycatch is the greatest threat to the recovery of thorny skates in Canada today. 

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