It's Raining Catsharks and Dogfish
Updated: Jan 13, 2022
When many people hear the term 'shark' they often imagine a toothy, large, dangerous predator, like something they have seen in a James Bond film. However, the vast majority of "extant" sharks are relatively small and completely harmless to humans. Not the kind of shark you might say 'infests' the waters. In fact, there may be more sharks in the water than you expect... in the UK alone, there are as many as 40 different species of sharks, with 20 or more making British waters their permanent home year-round! Allow me to introduce you to some of these adorable little characters...
[Family- Scylliorhindae, Order- Carcharhiniformes]
The small spotted catshark (Scylliorhulnus canicula) is common in British waters year-round and happily, its population size is thought to be healthy. They can be found in the northeast Atlantic and the mediterranean Sea; from the UK, north to Norway, south to Senegal. These catsharks prefer sandy, gravely "substrates" over "continental shelves" and "continental slopes", up to depths of 400m. These sharks are "generalist" feeders; eating all different kinds of animals they find in the "benthic environment, including mollusks, crustaceans, small fish, worms and star fish. They grow to a maximum size of 1m and are not a threat to humans (barring you try to pick one up and get a nasty nip, which would serve you right!).
The nursehound (Scylliorhulnus stellaris) looks very similar to its aforementioned cousin, but differs in being larger (up to 1.6 m total length), having larger spots and having nasal flaps which do not extend to the mouth. They have a similar range to their cousins in the northeastern Atlantic, but are found more commonly amongst rocks or algae, at comparably
shallow depths up to 60m. These sharks are also benthic predators, feeding on bony fishes, crustaceans, cephalopods, and other, smaller species of sharks (Compagno, 1984).
[Family- Triakidae, Order- Carcharhiniformes]
The tope shark is a seasonal visitor to British waters, as it has a global distribution and undergoes large-scale, annual migrations. Tope can reach 2m in length and they feed mainly on "benthic" and "pelagic" fish (meaning those found near the sea floor and those found in the middle of the water column respectively). The tope is commonly targeted in fisheries for its liver oil, fins and meat. In the UK, tope meat can even be found being sold as a replacement for cod or haddock in fish and chip shops! Tope are now classified as 'vulnerable' by the International Union for the Conservation of Nature (IUCN). This means that their populations are declining and conservation measures are required to protect the species (Hobbs et al, 2019).
[Family- Triakidae, Order- Carcharhiniformes]
The smooth hounds are so-called because they often form large groups, like a pack of dogs.
The common smooth hound (Mustelus mustelus) and starry smooth hound (Mustelus asterias) are both thought to be found in waters of the UK, but they are commonly misidentified because of their similar appearances. Both have similar distributions in the eastern Atlantic ocean and the Mediterranean Sea, and both feed predominantly on crustaceans and mollusks. The differ in size; the common smooth hound reaches a maximum size of 2 m, where the starry smooth hound can only reach around 1.4m total length. The noticeable difference between these two species is apparent in their population declines; where the starry smooth hound is considered 'least concern', the common smooth hound is classified as 'vulnerable' by the IUCN. When the smooth hounds are landed in fisheries they are often lumped together as Mustelus spp. in the landing reports, which can make it very challenging to monitor their catches and population declines.
[Family- Squalidae, Order- Squaliformes]
The spiny dogfish (Squalus acanthias) is so named for its two impressive spines which project out of the top of the dorsal fins. These spines can certainly cause you a nasty injury if you ever make the mistake of handling a spiny dogfish. The spines evolved to defend the dogfish and make it unpalatable to predators. Yet, spiny dogfish are formidable predators themselves; hunting in large groups (of up hundreds or even thousands of individuals) for crustaceans, small fishes, squid and jellyfish, and other invertebrates like sea cucumbers. Spiny dogfish were once one of the most abundant shark species globally, but overfishing now means that the IUCN now lists them as 'vulnerable' globally and they are further classified as 'critically endangered' in the northeastern Atlantic (Compagno, 1984 & Lack, 2006).
Fishing is a huge industry in the UK. A recent report by the New Economic Foundation (NEF) found that the UK is responsible for the highest amount of overfishing of any EU country, with 2 million tonnes of fish being landed annually above the level advised by scientists. This makes UK fisheries significantly unsustainable.
"The Government must now demonstrate that it is committed to ending the destructive overfishing... This means making, and sticking to, regional agreements that respect fish population limits."
- Rebecca Hubbard, Program Director of Our Fish Campaign Group
In order to protect endangered sharks and ensure that UK fisheries do not decimate commercial fish populations to the point of collapse, it will be important to ensure sensible quotas (based on scientific advice) are firmly set in the near future.
You can also sign the petition demanding sustainable UK fisheries.
Scientists have actually now discovered that sharks have come back to the River Thames! To learn more you can check out London Calling.
Compagno LJV (1984). Shark of The World: An Annotated and Illustrated Catalogue of Shark Species Known to Date. FAO Species Catalogue. Access online.
Hobbs CAD, Potts RWA, Bjerregaard-Walsh M, Usher J & Griffiths AM (2019). Using DNA Barcoding to Investigate Patterns of Species Utilisation in UK Shark Products Reveals Threatened Species on Sale. Scientific Reports, 9:1, doi: 10.1038/s41598-018-38270-3. Access online.