New study furthers understanding of Atlantic bluefin tuna genome
by NOAA Fisheries 21 Nov 2023 19:47 UTC
Atlantic Tuna © iStock
The commercially important Atlantic bluefin tuna (Thunnus thynnus), a large migratory fish, has experienced notable recovery aided by accurate resource assessment and effective fisheries management efforts.
Traditionally, this species has been perceived as consisting of eastern and western populations, spawning respectively in the Mediterranean Sea and the Gulf of Mexico, with mixing occurring throughout the Atlantic.
However, recent studies have emerged challenging this assumption by revealing weak genetic differentiation and identifying a previously unknown spawning ground in the Slope Sea used by Atlantic bluefin tuna of uncertain origin. To further understand the current and past population structure and connectivity of Atlantic bluefin tuna, we have assembled a unique dataset including thousands of genome-wide Single Nucleotide Polymorphisms (SNPs) from five hundred larvae, young of the year and spawning adult samples covering the three spawning grounds and including individuals of other Thunnus species.
Our analyses support two weakly differentiated but demographically connected ancestral populations that interbreed in the Slope Sea. Moreover, we also identified signatures of introgression from albacore into the Atlantic bluefin tuna genome, exhibiting varied frequencies across spawning areas, indicating strong gene flow from the Mediterranean Sea towards the Slope Sea. We hypothesize that the observed genetic differentiation may be attributed to increased gene flow caused by a recent intensification of westward migration by the eastern population, which could have implications for the genetic diversity and conservation of western populations. Future conservation efforts should consider these findings to address potential genetic homogenization in the species.
Read the full study here...
Fun facts about Atlantic tunas
In celebration of our Atlantic Tunas Art Contest, we wanted to share some interesting facts and hopefully inspire this year's young artists!
1. Tunas come in many sizes
Western Atlantic bluefin tuna are the largest of the Atlantic tuna species. They can grow up to 13 feet long and weigh up to 2,000 pounds! They have a long lifespan, living 20 years or more, and generally don't spawn until they are 8 years old.
Atlantic skipjack tuna are among the smallest, weighing in at 40 pounds and measuring around 3 feet long. They grow up fast, spawn when they are 1 year old, and have a relatively short lifespan of 7 years.
2. Tunas are very fast swimmers
Thanks to their unique torpedo-shaped bodies, smooth skin, and streamlined fins, tunas are fast swimmers. Albacore tuna can swim faster than 50 miles per hour. This helps them catch prey, avoid predators, and cover a lot of ground quickly during annual migrations.
3. Bluefin tunas are warm blooded
Some tunas—like bluefin tunas—are warm-blooded, like mammals. They are able to keep their body temperature warmer than the water around them thanks to a specialized blood vessel structure, called a countercurrent exchanger. This gives them several advantages over cold-blooded fish.
Regulating their own temperature means tuna can live in a wide range of conditions, and can be found in arctic and tropical waters. The extra heat in their muscles gives them a boost in power and speed. It also helps them dive deep, reaching depths of 500 to 1,000 meters to search for food and to avoid predators.
4. Albacore tunas, like all tunas, never stop swimming
If you could follow an albacore tuna around the ocean, you would notice something strange: it never stops moving. Like all fish, they need oxygen to fuel their bodies, pulling it from the water through special organs called gills. Unlike other fish, they lack the structures needed to pump water over their gills.
Instead, albacore tuna swim with their mouths open, allowing water to flow in and wash over their gills. They have adapted to life on the go, with their very long pectoral fins allowing them to save energy by "gliding" through the water.
5. Tunas travel the oceans in schools that can number in the thousands
Tunas travel together in groups called schools. They migrate great distances between hunting grounds and spawning grounds. These schools can include hundreds or thousands of fish. For example, albacore tunas travel together in schools that can be up to 19 miles wide!
Swimming in schools gives tuna an edge over prey when hunting. Having many eyes scanning the sea also helps them spot and avoid predators. It's not unusual to see schools that include a variety of tuna species including albacore, skipjack, yellowfin, and bluefin.
6. Tunas are known for being top predators—but they are also prey
All tuna species are predators. Their torpedo-shaped bodies give them an advantage over slower, less maneuverable species and their sharp vision helps them catch prey. Tunas eat a varied diet including fish, crustaceans, and squid. The smaller skipjack tuna are opportunistic feeders, preying on a variety of fish including herrings, crustaceans, cephalopods, mollusks, and sometimes other skipjack tunas.
Tunas are also a favorite prey species for top ocean predators. A tuna's speed and agility comes in handy when avoiding hungry sharks, billfish, and toothed whales. Smaller tuna species (like skipjack) and juveniles also have to avoid other larger tunas looking for a meal.
7. Tunas have their own day!
May 2 is World Tuna Day—named by the United Nations to highlight the global importance of sustainably managing tuna fishing stocks in the world's oceans. This ensures they will be swimming in the world's oceans long into the future. NOAA Fisheries, with the help of tuna fishermen, sustainably manage tuna fisheries in U.S. waters.
8. Fishing for tuna is an ancient practice
Cave paintings found near Sicily provide the best evidence that humans have been fishing for tuna for a long time. The paintings feature bluefin tuna and date from around 9200 years BCE. Archeologists believe tuna were actively fished in the Mediterranean and have found evidence of this in Greece, Croatia, France, and Spain.