Marine Life & Conservation Blogs
Creature Feature: Electric Rays
In this series, the Shark Trust will be sharing amazing facts about different species of sharks and what you can do to help protect them.
This month we’re focusing on some shockingly (sorry) awesome rays – the electric rays!
The electric rays (Torpediniformes) are unique – as they are the only rays who have a specialised electric organ. This means they are able to produce a shock of 20-200 volts! Now there are some skates that can do this. But they don’t produce a shock in quite the same way.
Electric ray bodies are thick and flabby. This generally means they’re not popular for human consumption. Combined with their powerful electric shock, fishers tend to avoid them and quickly discard any that are caught as bycatch.
Their ability to produce a coordinated, external electric shock is known as electrogenesis. It’s a complicated process. But essentially – the ray is able to stimulate modified muscle cells to produce the shock. These muscle cells sit in a honeycomb pattern. Within a kidney-shaped organ in the front of either side of the disc. Used as a defensive or predatory reflex, the shock that species can produce can range from a mild warning pulse all the way up to a 200 volt shock used to incapacitate prey.
Marbled Torpedo Ray (Torpedo marmorata)
The Marbled Torpedo Ray is one species of electric ray. It’s found in the coastal waters of the Eastern Atlantic, from the North Sea and English Channel down to South Africa, including the Mediterranean Sea. Nocturnal and solitary, they reside at depths of 10 – 370m on rocky reefs, seagrass beds and sandy or muddy flats.
The species was used in Ancient Greece and Ancient Rome, its shocks used to treat conditions like chronic headaches! In the modern world, along with other electric ray species, it is caught and used as a “model organism” in biomedical research. However, the species is not commercially targeted by fishers, and bycatch is discarded due to its low commercial value.
The Marbled Electric Ray feeds predominantly on bony fishes and can produce a shock of up to 70-80 volts. It ambushes its prey from the seabed, then uses its wings to engulf prey whilst emitting electrical shocks to stun them. New-born rays are immediately capable of using electricity to hunt.
Within the Mediterranean Sea it’s the most common species of electric ray, and the population is considered stable. Despite a lack of largescale fisheries targeting this species, the population is thought to be decreasing outside of the Mediterranean. This is suspected to be due to bycatch mortality and pressure from localised fishing.
SCIENTIFIC NAME: Torpedo marmorata
FAMILY: Torpedinidae
MAXIMUM SIZE: 100cm, usually to 60cm.
DIET: Bony fishes.
DISTRIBUTION: North Sea and English Channel down to South Africa, including Mediterranean Sea.
HABITAT: Coastal Waters – rocky reefs, seagrass and mudflats.
GLOBAL CONSERVATION STATUS: Vulnerable
EUROPE CONSERVATION STATUS: Least Concern
For more amazing facts about sharks and what you can do to help the Shark Trust protect them visit the Shark Trust website by clicking here.
Banner Image: Leopard Torpedo Ray – ©Maya Parf via Shutterstock
Image – Marbled Torpedo Ray – © Kim Briers via Shutterstock
Marine Life & Conservation Blogs
Creature Feature: Dusky Shark
In this series, the Shark Trust will be sharing amazing facts about different species of sharks and what you can do to help protect them.
This month we’re taking a look at the Dusky Shark, a highly migratory species with a particularly slow growth rate and late age at maturity.
Dusky sharks are one of the largest species within the Carcharhinus genus, generally measuring 3 metres total length but able to reach up to 4.2 metres. They are grey to grey-brown on their dorsal side and their fins usually have dusky margins, with the darkest tips on the caudal fin.
Dusky Sharks can often be confused with other species of the Carcharhinus genus, particularly the Galapagos Shark (Carcharhinus galapagensis). They have very similar external morphology, so it can be easier to ID to species level by taking location into account as the two species occupy very different ecological niches – Galapagos Sharks prefer offshore seamounts and islets, whilst duskies prefer continental margins.
Hybridisation:
A 2019 study found that Dusky Sharks are hybridising with Galapagos Sharks on the Eastern Tropical Pacific (Pazmiño et al., 2019). Hybridisation is when an animal breeds with an individual of another species to produce offspring (a hybrid). Hybrids are often infertile, but this study found that the hybrids were able to produce second generation hybrids!
Long distance swimmers:
Dusky sharks are highly mobile species, undertaking long migrations to stay in warm waters throughout the winter. In the Northern Hemisphere, they head towards the poles in the summer and return southwards towards the equator in winter. The longest distance recorded was 2000 nautical miles!
Very slow to mature and reproduce:
The Dusky Shark are both targeted and caught as bycatch globally. We already know that elasmobranchs are inherently slow reproducers which means that they are heavily impacted by overfishing; it takes them so long to recover that they cannot keep up with the rate at which they are being fished. Dusky Sharks are particularly slow to reproduce – females are only ready to start breeding at roughly 20 years old, their gestation periods can last up to 22 months, and they only give birth every two to three years. This makes duskies one of the most vulnerable of all shark species.
The Dusky Shark is now listed on Appendix II of the Convention on the Conservation of Migratory Species (CMS), but further action is required to protect this important species.
Scientific Name: Carcharhinus obscurus
Family: Carcharhinidae
Maximum Size: 420cm (Total Length)
Diet: Bony fishes, cephalopods, can also eat crustaceans, and small sharks, skates and rays
Distribution: Patchy distribution in tropical and warm temperate seas; Atlantic, Indo-Pacific and Mediterranean.
Habitat: Ranges from inshore waters out to the edge of the continental shelf.
Conservation status: Endangered.
For more great shark information and conservation visit the Shark Trust Website
Images: Andy Murch
Diana A. Pazmiño, Lynne van Herderden, Colin A. Simpfendorfer, Claudia Junge, Stephen C. Donnellan, E. Mauricio Hoyos-Padilla, Clinton A.J. Duffy, Charlie Huveneers, Bronwyn M. Gillanders, Paul A. Butcher, Gregory E. Maes. (2019). Introgressive hybridisation between two widespread sharks in the east Pacific region, Molecular Phylogenetics and Evolution 136(119-127), https://doi.org/10.1016/j.ympev.2019.04.013.
Marine Life & Conservation Blogs
Creature Feature: Undulate Ray
In this series, the Shark Trust will be sharing amazing facts about different species of sharks and what you can do to help protect them.
This month we’re looking at the Undulate Ray. Easily identified by its beautiful, ornate pattern, the Undulate Ray gets its name from the undulating patterns of lines and spots on its dorsal side.
This skate is usually found on sandy or muddy sea floors, down to about 200 m deep, although it is more commonly found shallower. They can grow up to 90 cm total length. Depending on the size of the individual, their diet can range from shrimps to crabs.
Although sometimes called the Undulate Ray, this is actually a species of skate, meaning that, as all true skates do, they lay eggs. The eggs are contained in keratin eggcases – the same material that our hair and nails are made up of! These eggcases are also commonly called mermaid’s purses and can be found washed up on beaches all around the UK. If you find one, be sure to take a picture and upload your find to the Great Eggcase Hunt – the Shark Trust’s flagship citizen science project.
It is worth noting that on the south coasts, these eggcases can be confused with those of the Spotted Ray, especially as they look very similar and the ranges overlap, so we sometimes informally refer to them as ‘Spundulates’.
Scientific Name: Raja undulata
Family: Rajidae
Maximum Size: 90cm (total length)
Diet: shrimps and crabs
Distribution: found around the eastern Atlantic and in the Mediterranean Sea.
Habitat: shelf waters down to 200m deep.
Conservation Status : As a commercially exploited species, the Undulate Ray is a recovering species in some areas. The good thing is that they have some of the most comprehensive management measures of almost any elasmobranch species, with both minimum and maximum landing sizes as well as a closed season. Additionally, targeting is entirely prohibited in some areas. They are also often caught as bycatch in various fisheries – in some areas they can be landed whilst in others they must be discarded.
IUCN Red List Status: Endangered
For more great shark information and conservation visit the Shark Trust Website
Image Credits: Banner – Sheila Openshaw; Illustration – Marc Dando
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