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Episode 238: Bye Bye Bluefin Tuna

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While tuna is a fish many eat around the world, these fish are heading towards extinction. This is especially true of the most prized Bluefin Tuna. In fact, one 600 lb. Bluefin Tuna sold for $3 million USD at a market in Japan making this fish one highly sought after. The result is, Bluefin Tuna now number only 3.3% of their historic population. This is also distressing because tuna are some of the most unique and amazing fish in our world’s oceans. They exhibit especially unique physiology and behaviors not observed in other fish. The good news is, conservation efforts are being made around the world to not only protect Bluefin Tuna, but the other tuna species. We have so much to learn about our oceans and all the species that inhabit it.

Blue Fin Tuna History

Fish are some of the oldest animals on Earth. Specifically, Bluefin Tuna belong to the class Actinopterygii, which are the ray finned bony fishes. Fish first appeared around 530 million years ago! It was during tis period where the planet experienced the Cambrian Explosion, which took place over 25 million years, and many species to include bony fishes emerged. Fish were present before there were even trees on the planet, which first emerged 385 million years ago.

Tunas did emerge until after the last great mass extinction, 55 to 60 million years ago. Today’s “true tunas” did not emerge until around 10 million years ago. They belong to the Scombridae family, which is the “mackerel” family. The tribe is called Thunnini, and is where tunas are classified. The species include:

  • genus Thunnus: albacores and true tunas
    • subgenus Thunnus (Thunnus): bluefin group
    • subgenus Thunnus (Neothunnus): yellowfin group
  • genus Katsuwonus: skipjack tunas
  • genus Allothunnus: slender tunas
  • genus Auxis: frigate tunas
  • genus Euthynnus: little tunas

Blue Fin Tuna Physiology

Tuna are some of the largest fish in the ocean, to even include sharks. The Atlantic Bluefin Tuna are the largest of any tuna species. They can reach a length of 15 feet (4.5 meters) and weigh upwards of 2000 lbs. (900 kg). However, due to overfishing and the massive decline in tuna around the world, it would be quite rare to find a specimen this large today.

Another fascinating fact about the Bluefin Tuna is they are some of the fastest fish in the ocean. They can swim up to 43 MPH (70 KPH). The body shape of a tuna has evolved to be as streamlined as possible allowing them to swim this fast. Additionally, their muscling allows them to swim over great distances, and is one reason they are so prized by humans. The red muscling is used for sustained swimming and provides greater oxygen to their muscles to aid them. White muscling, seen in many fish species, is for more quick and short bursts of speed.

Tuna are considered “semi warm blooded.” Most fish are cold blooded, meaning their blood temperature matches the water they are swimming in. However, tuna are very unique, in that their muscles generate body heat that is sustained in the blood. Through a counter-current exchange blood system, the heat produced by their muscles while swimming circulates in their bodies. This helps them maintain a body temperature above that of the ambient water. This also helps them swim faster and longer.

From: The Tuna Fishing Industry: A New Outlook on Fish Protein Hydrolysates N. Huda Herpandi, A. Rosma, W.A. Wan Nadiah

Bluefin Tuna are considered an apex predator in our oceans. They eat a variety of prey as they mature, but as adults they focus on squid and particularly herring and sardines. Not much can prey upon an adult Bluefin Tuna due to their size and speed. Humans are their main threat.

Blue Fin Tuna Conservation

Almost all species of Tuna are being overfished in our world’s oceans and heading towards extinction  Some stocks are fished sustainably. Of the “true tunas” they are classified as:

  • Southern Bluefin Tuna – Critically Endangered
  • Atlantic Bluefin Tuna- Endangered
  • Pacific Bluefin Tuna- Vulnerable
  • Albacore Tuna- Near Threatened
  • Bigeye Tuna- Vulnerable
  • Yellowfin Tuna- Near Threatened
  • Blackfin Tuna- Least Concerned

Of the other tuna species, the one highly consumed is Skipjack Tuna. They are classified as Least Concern and the one currently fished at sustainable levels.

Bluefin Tuna are at around 3% of their historical populations. They are in serious trouble. However, Japan and other countries are working hard to conserve what Bluefin Tuna are left. Japan has turned to aquaculture to meet the large demand for Bluefin Tuna across the world.

You can read more about where we are with our fish stocks in the world’s oceans by going HERE


July 28, 2021
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