Meet the Incredible Venomous Sharks of the Thames River

Written by Kristen Holder
Updated: June 21, 2023
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Key Points:
  • London’s Thames River was declared biologically dead in the 1960s due to pollution in the water. Efforts to remove toxic waste were successful and it is now home to more than 115 species of fish.
  • Spurdogs, also known as spiny dogfish, are venomous sharks that started showing up in the Thames due to warming and rising seawater of their native deep water habitats.
  • Spurdogs’ venom is secreted through their spines to subdue prey. While the potency of the venom is still being studied, side effects from an injection of spurdog venom into a human include severe pain and swelling.

What is a venomous shark? Why are there venomous sharks in the Thames River? It seems incredible that we’d ask these questions. The Thames River runs through London, and it was declared biologically dead in the 1960s. Efforts to re-establish sound habitats for animals have led to a revival of life in the channel.

There are more than 115 species of fish and 92 species of birds now residing in the river system. The river is 215 miles long, and the Thames River becomes an estuary before it reaches the North Sea.

Some of the animals that now reside in and around the Thames are seals, oysters, seahorses, eels … and venomous sharks. What is a venomous shark, and why are they living in London? We’re going to sort out some details now.

The Spurdog

Spiny Dogfish (Squalus acanthias) at the south coast of Norway

Spurdogs, which arrived in the Thames due to warming and rising seawater, secrete venom through their spines.


Spurdogs are also known as spiny dogfish, and they were almost overfished into extinction. These sharks have recently started showing up in the Thames due to warming and rising seawater and are not returning to an ancestral habitat.

Spurdogs are slender sharks with venomous spines — the front part of their dorsal fins sports their little daggers. Like most aggressive adaptations, these spines are meant to help subdue prey.

The venom is secreted through the spines. It comes at its prey in a bow shape so it can use its dorsal spines on its victim. Spurdogs are prey to goosefish, red hake, cod, orcas, and larger sharks.

These sharks prefer deep water, but they come into the shallows to feed and breed. They use the warming waters in the Thames estuary to birth their pups. The pups live in the Thames estuary for up to two years before going back to their preferred deep-water home.

Spurdogs are dogfish because they hunt in packs. They keep schooling fish in a group so they’re easier to feast on. Groups of over 100 individuals get together to hunt like this. They don’t feed much in the winter, but when it’s time to come closer to shore to birth, they participate in this feeding ritual.

What Is a Venomous Shark?

When we think of animals that are venomous, spiders, jellyfish, snakes, and lizards come to mind before a shark. With more than 100,000 venomous animal species on the planet, there are bound to be a few oddities.

Two thousand of those venomous animals are in the same fish family as sharks. The incredible venomous sharks of the Thames River are an example of these fish. There are also venomous weever fish and stingrays in the Thames as well.

If we look at all venomous fish combined, dorsal spines are the delivery system for 95% of fish. On the spurdog, the spine is in front of the dorsal fin with the same curvature as the fin.

Not as much is understood about fish venom in comparison to snake venom, but some scientists are calling for more research since investigations into the venoms of other animals have led to some pharmaceutical breakthroughs.

How Potent Is the Spurdog’s Venom?

Side effects from a successful human injection of spurdog venom include severe pain and swelling. The venom itself hasn’t gone through many scientific tests, but edema can result from envenomation. Future research is being called for so its potential benefits can be explored.

There are some sources out there that say the spiny dogfish’s envenomation has been fatal, but there have been no studies conducted on this topic. Right now, the exact effects, delivery method, and complications are a mystery.

This shark is venomous and not poisonous because it’s not dangerous to touch them. They aren’t coated in anything that makes their normal body inherently toxic.

The spikes inject venom only when the shark intends. A special venom gland below the spikes is responsible for toxin production. Since the venom comes from this gland and through the spike to be injected, it is venom and not poison.

What Other Incredible Sharks Are Found in the Thames?

Tope shark

Tope sharks are nonvenomous and can be found in the Thames.

©D Ross Robertson / This image or file is a work of a Smithsonian Institution employee, taken or made as part of that person’s official duties. As a work of the U.S. federal government, the image is in the public domain in the United States.

Starry smoothhounds and tope sharks are other sharks in the Thames. Neither shark is venomous.

The tope shark grows up to six feet long and weighs up to 106 pounds. It eats crustaceans and fish, and it has never intentionally attacked a human. Tope sharks are migratory, and sharks that were tagged in the UK were spotted in Iceland, the Canary Islands, and the Azores.

Tope sharks like to munch on whatever fish is convenient. Some staples are squid, rockfish, and sardines. They’re eaten worldwide and are sometimes used in fish and chips as a substitute for halibut or cod.

The starry smoothhound reaches up to four feet in length and weighs up to 25 pounds. It chows down on mollusks, crustaceans, lobster, and shellfish. It likes to hang out near the surface and regularly swims to a depth of 600 feet.

Why Was the Thames Declared Dead in the 1960s?

River Thames

The Thames was declared biologically dead due to unbridled sewage disposal over an extended period.

©Csaba Peterdi/

There was so much pollution in the water of the Thames in London that the oxygen levels couldn’t support life. However, the efforts to remove toxic waste from the water have increased the oxygen level enough to support incredible sharks and other marine animals.

One of the major reasons that the Thames was declared dead was unbridled sewage disposal over an extended period. However, the development of sewage treatment plants and laws put in place regarding industrial waste helped to alleviate the problem.

What is the Thames Tideway Tunnel?

London’s current sewer system is from the Victorian era, and excess sewage that the system can’t handle still spills into the Thames. The 150-year-old infrastructure is not only old, but it was also designed to handle only about a quarter of today’s population.

Today, untreated raw sewage still ends up in the river in mass quantities. An almost 16-mile sewage tube is being built under the River Thames to solve this.

This project has been ongoing, and it was originally slated for completion in 2024. As with most major construction problems globally, the disruption of supply chains during the COVID-19 pandemic bumped the expected completion date to 2025. The Thames Tideway Tunnel will solve the pollution issue. It will catch 95% of the waste that now spills into the Thames Estuary and keep it from polluting the river.

The photo featured at the top of this post is © Csaba Peterdi/

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About the Author

Kristen Holder is a writer at A-Z Animals primarily covering topics related to history, travel, pets, and obscure scientific issues. Kristen has been writing professionally for 3 years, and she holds a Bachelor's Degree from the University of California, Riverside, which she obtained in 2009. After living in California, Washington, and Arizona, she is now a permanent resident of Iowa. Kristen loves to dote on her 3 cats, and she spends her free time coming up with adventures that allow her to explore her new home.

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