How well do you know your Batoids?

When people think of sharks, they think of the majestic White (Carcharodon carcharias), the sleek Blue (Prionace glauca), or the fast Shortfin mako (Isurus oxyrinchus).

White shark; photo credit: Raul Touzon

White shark; photo credit: Raul Touzon

Blue Shark

Shortfin mako

 

What is a Ray?

However, many people do not know that sharks have other relatives. Elasmobranchs refers to fishes that have a cartilaginous skeleton, no swim bladders, and have five to seven gill slits. We will be focusing on the batoids, aka ‘flatsharks’. People might be familiar with the word ‘ray’, but what defines a ray? A ray is a flattened shark, with the gill slits only visible on the ventral side. Currently, there are six orders of elasmobranchs taxanomists have defined as batoids. They include: Pristiformes (Sawfishes), Rhiniformes (Wedgefishes), Rhinobatiformes (Guitarfishes), Torpediniformes (Electric Rays), Myliobatiformes (Stingrays), and the Rajiformes (Skates).

Here are what some of these batoids look like:

Dwarf sawfish (Pristis clavata)

Black Spotted Torpedo Ray (Torpedo fuscomaculata)

Shovelnose guitarfish (Rhinobatos productus)

Bowmouth guitarfish (Rhina ancylostoma)

Smoothnose wedgefish (Rhynchobatus laevis)

As you can see even these flat sharks are variable in morphology! If you are interested in how these orders are related in-depth, please check out the Tree of Life! We will go through all these different orders at a later time, but let’s focus on two orders: Myliobatiformes (Stingrays), and the Rajiformes (Skates). People often confuse these two groups, since they have similar body plans, but let’s take a closer look at their differences.

Stingray vs Skate

Difference between Stingrays and skates. Photo credit from: http://www.flmnh.ufl.edu/fish/education/questions/raybasics.html

On the left is a stingray or ray, and on the right is a skate. Skates lack the venomous stingers on their tails; instead they have thorns on their body and tail. Some skates also have thorns on the edge of their wings. Skates have a longer rostrum or snout, and are completely flat compared to stingrays. Dentition (teeth) also differ in these two orders. Skates have small single cusp teeth to feed on benthic invertebrates, while most rays have fused dental plates used to crush invertebrates such as crustaceans, bivalves, and snails. Manta rays (Manta alfredi, M. birostris) have teeth on the lower jaw, but rely on their gill rakers to collect plankton.

Dentition of the Big skate (Beringraja binoculata). Photo credit: Cathleen Bester

 

Dental plates of the Spotted Eagle Ray (Aetobatus narinari). Photo credit: Cathleen Bester

Another difference between these groups is their mode of reproduction. Skates are oviparous (egg-laying). They lay egg capsules that are commonly found along the beaches called mermaid purses. Stingrays on the other hand, are viviparous (live-bearing).

Various stages in the development of Arctic skate (Amblyraja hyperborea). From developing embryos to neonate (Photo: Arve Lynghammar)

Neonate Round stingray/ Haller’s Round Ray (Urobatis halleri); photo credit: Tennessee Aquarium

Species of Concern

As diverse as these groups are, all batoids face a common threat. Many are caught as bycatch, species that are targeted in commercial fisheries, by longlines and trawl nets, and discarded back to sea. These incidents commonly occur where fishing practices are not regulated or heavily enforced. Many of these discarded species do not survive. Like sharks, many batoids are also long-lived and do not mature till very late, increasing their vulnerability to being overfished.

Different species of batoids and fish discarded, mortality is very high in bycatch. Photo credit: Brian J. Skerry

Save the Rays, be aware!

As consumers, it is important to know where your seafood is from and how it is practiced. For more guidance about how to be seafood savvy, please check out Seafood Watch, OceanWise, and Oceana for updated information. Our batoids friends need your help to protect them! After all, who doesn’t want to see these smiling (skate) faces greeting you at aquariums and out in the wild?

Neonate skates swimming around. (Photo credit: Mandy Reid)

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