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Marine Life & Conservation Blogs

Creature Feature: Big Skate



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 the Big Skate, a species which might just have the most self-explanatory of all common names. It’s big and it’s a skate.

The largest species of skate in North American waters, the largest Big Skate (Beringraja binoculata) on record was measured to be 2.4m long! Found only in the north-eastern Pacific Ocean, these skate can be found at depths anywhere between 3-800m, although they are more commonly found shallower.  Big Skate have a distinctive diamond-shaped body and likely have the largest eggcases in the Rajidae family, measuring 22.8-30cm long!

In addition to their great size, their eggcases are remarkable because they usually contain 3-4 embryos (up to 8!), making them one of the only species of elasmobranch to contain multiple embryos in their eggcases! They have been known to produce up to 360 eggcases per year in captivity. Now let’s assume an average of 3.5 embryos per eggcase, then in one year, they have the potential to produce 1,260 babies! It is therefore one of the most reproductive of all elasmobranchs[1]. In the wild of course, not all of the embryos would be successful due to predation and other natural factors. Elephant seals have sometimes been recorded to eat Big Skate eggcases.

Like many other species of skate, they have large ‘eyespots’ on the pectoral fins which are thought to be used to deceive predators and make them more hesitant to attack. This is a form of mimicry and can be found in butterflies, reptiles, cats, birds and fish. A great example are the eyespots on the feathers of peacocks!

One theory behind their function is that the resemblance of the eyespots to the eyes of predators’ own predators produces an intimidating effect[2]. But other theories argue that it is simply how noticeable they are to predators that stimulates avoidance behaviour[3]. Other studies have found that it can be a form of ‘self-mimicry’, wherein the eyes draw the predator’s attention away from its most vulnerable body parts. They can also play a role in courtship behaviours.

Scientific Name: Beringraja binoculata

Family: Rajidae

Maximum Size: 290cm (total maximum length)

Diet: Marine invertebrates such as shrimps, worms and clams, sometimes small fish.

Distribution: North-eastern Pacific Ocean, from Alaska to Baja California.

Habitat: At depths of 3-800m. Commonly founder shallower – between 100-200m in sandy/muddy coastal bays and estuaries.

Conservation Status: In general, the Big Skate is not a major fishery target, although there are commercial and recreational fisheries in Californian waters where it is commonly landed as bycatch. Together with Longnose Skate*, these two species account for 99% of the skate landings in British Columbia[4]. They are currently listed as Least Concern on the IUCN Red List, however there are a lack of species-specific stock assessments in certain areas, and so this is just an estimate.

IUCN Red List Status: Least Concern

*Note, the common name ‘Longnose Skate’ can refer to several species of skate. In northeast Atlantic and Mediterranean waters, it refers to Dipturus oxyrinchus. In southeastern Australian coasts, the skate is Dentiraja confusa. In the northeast Pacific, the name refers to Beringraja rhina.

For more great shark information and conservation visit the Shark Trust Website

Photo Credits: Andy Murch

[1] Wallace, S. (2006). Seafood Assessment: Longnose Skate and Big Skate Raja rhina and Raja binoculata. SeaChoice. Blue Planet Research and Education.

[2] Karin Kjernsmo et al. Resemblance to the Enemy’s Eyes Underlies the Intimidating Effect of Eyespots, The American Naturalist (2017). DOI: 10.1086/693473

[3] Martin Stevens, Chloe J. Hardman, Claire L. Stubbins, Conspicuousness, not eye mimicry, makes “eyespots” effective antipredator signals, Behavioral Ecology, Volume 19, Issue 3, May-June 2008, Pages 525–531,

[4] Wallace, S. (2006). Seafood Assessment: Longnose Skate and Big Skate Raja rhina and Raja binoculata. SeaChoice. Blue Planet Research and Education.

The Shark Trust is the leading UK-based shark conservation charity. The team works globally to safeguard the future of sharks, and their close cousins, the skates and rays. Engaging with a global network of scientists, policymakers, conservation professionals, businesses and supporters, to further shark conservation. Established in 1997 to provide a voice for UK sharks, the Shark Trust has an ever-growing number of passionate supporters. And together we're creating positive change for sharks around the world. Want to join us and help protect sharks around the world? Click here!

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.


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),

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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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