You might imagine that glistening coral reefs or productive, rich coastal oceans might be the the areas where you could find the greatest abundance of sharks and rays. Yet in reality, of the some 1200 species that are known to science, the vast majority of sharks and rays actually live in the deep oceans. Many of these species remain mysterious and poorly understood thanks to the challenges we face trying to study them in their deep, dark habitats. However, this does not mean that these creatures are safe from human exploitation and many are regularly caught in fisheries all over the world. So which deepsea sharks and rays are targeted by fisheries? Why are they targeted? And is it really a big concern?
Big Blue
Our oceans are incredibly vast! Not only are they wide, but they are also very, very deep. The deepest parts of the ocean (in the Mariana Trench) can hit depths up to 10,935 meters! You might imagine that these alien landscapes are few and far between, but in fact, the "deep ocean" regions (that reach 200 metres or more below sea level) cover a huge area of our planet and they make up 98% of the whole ocean's volume! (Finucci et al, 2024)
In fact, so much of the ocean is inhospitable to humans, that we know very little about what life exists down there and to this day the deep oceans remain some of the least-explored of all ecosystems on Earth (Priede et al, 2006; Finucci et al, 2024).
However in recent years, advancing technology has allowed us to see some more of this mysterious world (to learn more see What Lies Beneath). So we now know that these inaccessible, little-explored regions - far from being dark, dead wastelands - are actually teeming with different species of sharks and rays, in all shapes and sizes (Ebert et al, 2021).
The Weird & the Wonderful
They may not be as iconic or easily recognisable as some of their shallow, coastal cousins, by deepsea sharks and rays are remarkable and very diverse. Ranging from large-bodied sixgills that can be several metres in length, to little catsharks barely reaching a metre from nose to tail. Some are plain in colour, others intricately patterned. In order to see in the gloom of the deep ocean, they are often equipped with especially large, gleaming eyes and some species have even adapted to glow in the dark (Ebert et al, 2021;Â Finucci et al, 2024).
To find out more about some of these fascinating characters head over to Deep Blue Sea and Twinkle, Twinkle, Little Shark.
One feature that is conserved across many of the deepsea sharks and rays, is that they are slow-growing and have a somewhat sedate lifestyle. This is because they live in a cold and relatively "unproductive" habitat, with limited food resources. Many deepsea sharks live on small animals such as invertebrates, like worms, crabs and lobsters. Some are "ambush predators" targeting small fishes and many also scavenge on the carcasses of animals that have sunk to the ocean floor (Ebert et al, 2021;Â Finucci et al, 2024).
From the Bottom to the Top
Sadly, hand-in-hand with our ability to use our advancing technology to learn more about these mysterious, deepsea animals, come those who would rather use it to exploit them.
Deepsea sharks were not regularly fished before 1970, but as our technologies have progressed, these heretofore inaccessible refuges in the oceans have become ever-more important targets for industrial fisheries (Finucci et al, 2024).
Whether they are directly targeted or caught as "bycatch", deepwater sharks and rays have great commercial value because their livers are especially rich in oils (particularly "squalene") which have many commericial uses; for fuel, as lubricants, for beauty products and in medicines such as supplements and some vaccinations (Finucci et al, 2024).
Going Down
A 2024 global assessment of the status of 2746 deepwater sharks and rays discovered that one in every seven species - more than 14% - is now threatened with extinction, according to the guidelines of the International Union for the Conservation of Nature. This is more than double the amount of species at risk compared to a similar study performed 10 years earlier, in 2014. Population sizes for some species have declined by more than 90% over just three generations (Finucci et al, 2024).
"1/7 deepwater sharks & rays are threatened [with] extinction... Â twice the number reported from the first global assessment in 2014"
The species most at risk are gulper sharks (family Centrophoridae), dogfishes (family Squalidae) and hardnose skates (family Rajidae). Yet as their habitats are still challenging to study, there are also many more Data Deficient species that have yet to be assessed, but could additionally be at serious risk (Finucci et al, 2024).
Gone Fishing
The massive declines in the populations of deepwater sharks and rays coincide perfectly with the advent of deepwater fishing. In fact, extraction in fisheries is the single most significant threat for 99% of deepwater sharks and ray species that have currently been assessed by the IUCN (Finucci et al, 2024).
As if this was not alarming enough, this group includes species with some of the most conservative life histories. This means that they are especially slow glowing and long-lived, and reach sexual maturity late in life, so have very low reproductive outputs. This means that their populations are incredibly slow to recover from declines - even more so than other sharks and rays - and they are especially sensitive to overexploitation in fisheries. It could take an incredibly long time for these species to start to rebound from these huge declines (Finucci et al, 2024).
Therefore, scientists are now calling for immediate trade and fishing regulations for deepwater sharks and rays in order to promote their recovery. Not only do these regulations need to be brought in straight away, but they will need to be especially strict in order to adequately protect such sensitive species. Just because they live in the deep oceans, it does not mean these animals are out of sight, out of mind... they are just as important to conservationists as any of their flashier, better known relatives (Finucci et al, 2024).
References
Ebert DA, Dando M& Fowler S (2021). Sharks of the World: A Complete Guide, Second Edition. Princeton University Press: UK..
Finucci B, Pacoureau N, Rigby CL, Matsushiba JH, Faure-Beaulieu N, Sherman CS, Vanderwright WJ, Jabado RW, Charvet P, Mejia-Falla PA, Navia AF, Derrick DH, Kyne PM, Pollom RA, Wills RHL, Herman KB, Kinattamkara B, Cotton CF, Cievas J-M, Dakey RK, Ebert DA, Fernando D, Fernando SMC, Francis MP, Huveneers C, Ishihara H, Kulka DW, Leslie RW, Neat F, Orlov AM, Rincton G, Sant GJ,Volvenko IV, Simpfendorfer C & Dulvy NK (2024). Fishing for oil and meat drives irreversible defaunation of deepwater sharks and rays. Science, 383:6687. Access online.
Gruber DF, Loew ER, Deheyn DD, Akkaynak D, Gaffney JP, Smith WL, Davis MP, Stern JH, Pieribone VA & Sparks JS (2016). Biofluorescence in catsharks (Scyliorhinidae): Fundamental description and relevance for elasmobranch visual ecology. Scientific Reports, 6:24751. Access online.
Priede IG, Froese R, Bailey DM, Bergstad OA, Collins MA, Dyb JE, Henriques C, Jones EG and King N (2006). The absence of sharks from abyssal regions of the world’s oceans. Proceedings of the Royal Society B, 273. Access online.
By Sophie A Maycock for SharkSpeak
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