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.

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.