What is the Largest Animal in the Sea?

There are some creatures in the world’s seas which can grow to truly gigantic sizes. As the article below discusses the sizes that blue whales, whale sharks and other species (some of which can be found in British waters) can grow to is truly amazing. Indeed, we known so little about some species such as the giant squid that we still do not know the true maximum size that they can reach. Read on to find out more about this topic.

The Biggest Creature in the Sea

Blue whale and Human

Size comparison between a fully grown blue whale and human.

The blue whale (Balaenoptera musculus) is undoubtedly the biggest creature in the sea, and is in fact the largest animal to have ever lived on plant earth – a fully-grown blue whale is double the size of the largest land-dwelling dinosaur that ever lived. They can grow to an absolute maximum of 33 metres in length (108 feet) and weigh 200 tons (400,000lbs), although most blue whales are smaller than this, averaging around 20 – 25 metres when fully grown. The true size of a fully-grown blue whale lends itself to being described in facts and statistics:

  • The arteries of a blue whale are approximately 10 inches wide.
  • The tongue of a blue whale weighs 3 tons.
  • At 10ft in length the blue whale has the largest penis in the animal world.
  • Each testicle of the blue whale weighs around 150lbs.
  • The heart of a blue whale is approximately the size of a saloon car.
  • New born blue whales are around 6-8 metres long at birth.
  • Baby blue whales feed on their mother’s milk – and can drink 50 gallons a day, meaning they can increase their weight by 200lbs every 24-hours!
  • Despite its vast size the blue whale is a filter feeder, eating only krill and other minute sea creatures. They can eat around four tons of krill each day.
  • As well as being the largest animal in the world, the blue whale is also the loudest. Its call can reach almost 190 decibels – to put that into perspective hearing damage beings at under 100 decibels. The loud, low frequency calls of the blue whales are used to communicate with each other, and can be transmitted for hundreds, possibly thousands of miles through the oceans.

While there were around 250,000 – 300,000 blue whales in the world at the start of the twentieth century the industrial hunting of this species led to a massive crash in their numbers.

Whale Graph

By the 1970s and 1980s there were bans and moratoriums on commercial whaling (ignored by Russia, Japan, Norway and Iceland who still hunt whales to this day under the pretence of ‘scientific research.’) However, these bans do seem to have had some effect with a modest rise in blue whale numbers from 5000 in the 1990s to approximately 10,000 – 25,000 alive in the world today. However, blue whales are still currently classed as Endangered by the IUCN (International Union for the Conservation of Nature).

In the discussion of largest sea creatures there is no debate – it is certainly the blue whale.

What is the Biggest Fish in the Sea?

The biggest fish in the sea (understanding fish to be all members of the cartilaginous fishes class of Chondrichthyes, the bony fish class of Actinopterygii and hagfish and lampreys) is the whale shark (Rhincodon typus). Despite its name this species in entirely a shark species, and not a mammal/whale at all.

Whale Shark and Human

Whale shark and human size comparison.

Whale sharks are found in the warm waters around the equator. Fully grown whale sharks can reach an absolute maximum size of 12.5 metres in length and weigh around 40,000lbs. Like the blue whale the whale shark is a filter feeder, with krill, fish eggs and microscopic marine creatures making up the majority of their diet, although they have also been observed feeding on small fish from time to time. In terms of behaviour whale sharks are gentle giants which pose no threat to humans – in fact people have been able to take rides on the back of whale sharks although conservationists and marine scientists take a dim view of this as it is an unnecessary way of disrupting and alarming these creatures. Whale sharks are also thought to live for around 150 years, making them one of the longest living creatures on the planet.

Whale Shark and People

Whale sharks are placid in their behaviour. In this picture tourist snorkel alongside a large whale shark off the coast of Cancún, Mexico.

Whale sharks are commercially targeted and the IUCN classifies this species as being Vulnerable.

What is the Biggest Bony Fish?

If we exclude Chondrichthyes (shark species) we can instead look at what is the biggest bony fish in the world. However, here there is some competition. The European sturgeon is found in the Capsian Sea, Black Sea and Adriatic Seas and migrates into fresh water to spawn. At its very largest the European sturgeon can grow up to 7 metres in length and weigh 4,000 lbs. However, it has been massively overfished and had its breeding patterns disrupted by the building of dams and other structures and the population of this species has declined by around 90-95% in the last few decades. Today the European sturgeon is classed as Critically Endangered by the IUCN and very large sturgeon are incredibly rare.

The ocean sunfish (Mola Mola) also joins the battle for the worlds largest bony fish. Sunfish are very strange looking, with a laterally compressed near circular body. At their largest sunfish can be 14ft by 14ft and weigh around 3,500lbs, certainly putting them up their with the largest bony fish. The other contender is the king of herrings (Regalecus glesne – also known as the Giant Oarfish). This is a mysterious eel-like fish which is poorly understood by the scientific community. However, what is clear is that king of herrings have been confirmed as growing to 11 metres in length, but evidence suggests that they may be able to reach lengths of 17-18 metres and weigh over 1000lbs.

Sunfish and Diver

A diver comes face to face with a sunfish off the coast of the Galapagos Islands.

The issue of the world’s largest bony fish is therefore a difficult and disputed issue. The king of herrings is almost certainly the world’s longest bony fish, but the European sturgeon and sunfish battle it out for the world’s heaviest.

Biggest Sea Creatures from Around the World

Colossal Squid

Colossal squid and human size comparison.

The colossal squid (Mesonychoteuthis hamiltoni) is the largest known squid species and the largest invertebrate known to science. They are thought to be able to reach 15 metres in total length, and weigh over 2000lb (length is from the tail to the end of the tentacles with the mantle (body) making up around half of the total length). Colossal squid are found around the Antarctic and feed aggressively on all manner of fish species they come across. However, they become prey themselves for large sperm whales, which battle and eventually defeat and feed on colossal squid. Indeed, sperm whales have been found with wounds caused by tentacles, indicating that squid may be able to grow larger than fifteen metres in length. The biggest colossal squid ever caught was a 10 metre, 1000lb specimen caught on a long-line off the coast of New Zealand in 2007. This specimen was thought to be a male but actually turned out to be a female, with males growing substantially larger than females this pointed to the fact that the potential size of colossal squid could be much larger than previously believed.

Colossal Squid New Zealand

The preserved carcass of the colossal squid caught off the coast of New Zealand in 2007. The squid was frozen and transported to the shore where it was donated to the Te Papa museum where it is preserved and on permanent display. Unfortunately the arms and tentacles of the squid disintegrated during the freezing process, meaning the specimen is substantially smaller than the 10 metre squid which was captured.

The Southern Elephant Seal (Mirounga leonina) is the largest seal species in the world, and is even larger than the walrus. The Southern elephant seal is found around the freezing waters of Antarctica. This species shows great differences in size between the sexes, with females growing to a (not inconsiderable) 10ft in length and 2000lb, but males growing to many times the size, reaching an amazing 20ft in length and 6000 – 7000lbs. However, in 1913 a Southern elephant seal was shot and killed in Possession Bay in South Georgia which weighed over 8000 tons and was 22ft 6ins in length.

Giant Isopod

Stuff of nightmares – the giant isopod lives on the seabed in deep water, a place where most people will be happy it stays!

Giant Isopod species such as Bathynomus giganteus lives in the deep waters of many of the worlds seas. While it does not sound like a giant at up to 15 inches in length it is when we consider that many isopods are just a few millimetres long, and some are so small they are measured in micrometres (one-thousandth of a millimetre). The giant isopod also truly looks like something out a horror film!

Other Notably Large Fish in British and Irish Waters

As mentioned both the ocean sunfish and the king of herrings have been found in British waters, with sunfish being increasingly common around the south west coast of England, possibly as a result of global warming. However, bluntnose six gilled shark are also present in UK and Irish waters, and may be able to reach 16 feet in length and 3000lb in weight.

Sixgill Shark

Swiss tourist Joe Waldis caught a 1056lb bluntnose sixgill shark in Irish waters in 2009. He was heavily criticised for killing the shark, rather than releasing it.

Indeed blue shark and porbeagle shark all both found in British waters from time to time and can grow to 12 – 13 feet, while another occasional visitor is the shortfin mako which can reach 14 feet in length and weights of over 1000lbs. However, it is the basking shark which grows to the largest sizes. Often sighted off the west coast of Scotland and parts of Ireland this species is a massive filter feeder which can reach, at an absolute maximum, 30 feet in length and 15,000lbs, but is more commonly 25 feet and 8000 – 9000lbs.

Other species can also reach surprising sizes. Cod can reach lengths of just over six feet and over 200lbs, although commercial pressure on this species means that the number of specimens reaching this size is immensely rare. Atlantic wolffish are a rare catch from the UK shore, with the British shore caught record currently standing at 12lb 12oz. However, this is a species capable of reaching lengths of five feet and weights in excess of 50lbs. The conger eel found in British and Irish waters (Conger conger, also known as the European conger eel) is actually the largest species of true eel in the world with eels of 7-8ft and 100lbs being fairly widespread, and evidence existing (in the form of commercial catches) indicating that this species could grow up to 12ft and weights greater than 300lbs. Other smaller, more common species can also reach surprisingly high sizes. Mackerel for example have an average shore caught weight of less than 1lb, with 2lb being an excellent catch from the shore, but the UK shore caught record is a monster mackerel of 5lb 11oz, caught at Berry Head Quarry, Brixham in 1982, with the boat caught record being a specimen of 6lb 2oz caught off the Cornish coast two years later in 1984.

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