Skates and rays are flat, cartilaginous fishes related to sharks. The cartilaginous fish are collectively known as Chondrichthyans. They are distinguished from the bony fishes by an internal cartilaginous skeleton and from jawless fishes by their true upper and lower jaw.
The taxonomic Class Chondrichthyes is divided into two subclasses, the Elasmobranchii (sharks, skates and rays) and the Holocephali (chimaeras). The Elasmobranchii are further divided into Super-orders, Orders, families, genera and species. There are about 500 shark species, while Order Rajiformes, the Batoid fishes, includes over 600 species of skates and rays worldwide. About 20 of these species are likely to be encountered in British fisheries, but only seven or eight are common in coastal waters.
The use of the words ‘skates and rays’ can be confusing. In scientific terminology, all members of the Suborder Rajoidei, which includes family Rajidae, are called skates. However, in the UK we traditionally use the name ‘skate’ only for species with long snouts (e.g. the Common Skate). Species with short snouts are usually called ‘rays’ (e.g. the Thornback and Cuckoo Rays). Both terms are given in this guide. Most other batoid fishes are known as rays (including the Stingrays, Cownose Rays, Eagle Rays, Devil Rays, and the Electric Rays or Torpedoes).
The mouth, nostrils and gill slits of skates and rays are always located on the underside of the fish, with the eyes and spiracles on the upper side. Many species also have spines and thorns on the upper surface and tail. It is easy to distinguish mature males, which have a pair of elongated claspers beneath the pelvic fins that are absent in females (and may be very hard to see in juvenile males).
Skates and rays are large, long-lived animals. Depending upon the species, they may take around five to ten years to mature and lay relatively few eggs (40 to 150 a year). Their low reproductive rate makes them particularly susceptible to overfishing, whether by trawls, longlines or set nets, because large juveniles are often caught and kept before they have started breeding and most species cannot rapidly replace the animals that are removed by fisheries. The smallest species tend to grow and breed most rapidly, but are of lower commercial value than larger animals.
For these same reasons, skates and rays tend not to support large commercial fisheries, which means that they have received far less attention from researchers and fisheries managers than the more economically-important bony fish species. These factors make the largest skates and rays among the most threatened species in British waters. For example, the Common Skate, the biggest and formerly one of the more abundant species around the British Isles, is now absent from much of its former range. Conversely, populations of some of the smallest species, such as the Cuckoo and Spotted Rays, are still healthy.
What is the difference between a skate and a ray?
One of the most frequently asked questions about skates and rays, especially those found in UK waters, is what is the difference between a skate and a ray? The problem is made more difficult by the fact that many of the species around the UK coastline are historically misnamed. For example, the Thornback Ray is actually a skate!
Skates differ from rays differ in a way which is especially relevant to eggcases:
Rays give birth to live young (via ovoviviparity) whereas skates give birth to young in eggcases – sometimes called mermaid’s purses (via oviparity). (Most sharks give birth to live young – via viviparity).
Historically however, skates and rays have been named, seemingly arbitrarily, as one or the other with no regard to their taxonomy. This has resulted in Blonde, Small-eyed, Thornback, Undulate, Spotted and Cuckoo skates being known as rays. Consequently, the terms skates and rays are used interchangeably throughout this site to reduce confusion as much as possible.
The method of birth is not the only difference between skates and rays though. The following text comes from the Reefquest Centre for Shark Research website and gives detailed information on how to tell the difference between rays and skates.
“Skates and rays can be difficult to differentiate. Both are flat and (with a few notable exceptions, such as the eagle and manta rays) bottom-dwelling elasmobranchs sharing a similar diamond or rhomboid shape. Some of the most familiar forms occur together in coastal habitats.
Adding to the confusion, the term 'ray' is also used in reference to the electric and torpedo rays (order Torpediniformes); fortunately, torpedinoids are unlikely to be confused with either skates or rays (especially if one handles a live specimen!), being easily identified by the following characteristics: a rounded pectoral disc; soft, flabby body; dorsal fins nearer the pelvic fins than the tail tip; and kidney-shaped electrogenic organs at the base of the pectoral fins."
Distinguishing skates from rays is rather subtle, but once one has learned their respective field marks, it is relatively easy to tell them apart.
Skates (order Rajiformes):
each pelvic fin divided into two lobes
tail relatively stocky, without a stinging spine
tail usually with two small dorsal fins near its tip and a tiny caudal fin (some forms lack dorsal and caudal fins)
many have enlarged, thorn-like scales ('bucklers') along the midline of back and tail; enlarged scales also occur along the side of the body (near the pectoral fin base) in some species
males have rows of enlarged scales near the eyes and wingtips (termed 'malar' and 'alar' spines, respectively)
Rays (order Myliobatiformes):
each pelvic fin with one lobe
tail relatively slender to whip-like, usually with a saw-edged stinging spine midway along its length
tail usually without a dorsal fin (in some forms, a single dorsal fin occurs near the tail base), caudal fin reduced and continuous or absent
no bucklers along the midline of back or tail (although Hypolophus sephen, sometimes called the 'Pearl Ray', has three rounded scales in the midline of its back) or along the side of the body
males lack malar or alar spines
In addition, skates are typically drab, brownish or greyish deep-water inhabitants, while many rays are boldly or colourfully patterned, shallow-water inhabitants. But these are generalizations only. Some skates are attractively blotched or spotted and others occur in shallow and even estuarine water, while some rays are plain greyish above, lighter below, and some live at great depths.”
Skates and Rays
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