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HomeLISTENING Meet the bluefin tuna, the toughest fish in the sea

[Mp4] Meet the bluefin tuna, the toughest fish in the sea

 

What’s as big as a polar bear, swallows its prey whole, and swims at 40 miles an hour? It’s not a shark or a killer whale, it’s the Atlantic bluefin tuna, the largest and longest-lived of the 15 tuna species. The Atlantic bluefin has a unique set of adaptations that make it one of the most dominant predators in the ocean.

 

It starts as a tiny hatchling in the Gulf of Mexico or the Mediterranean Sea, no bigger than a human eyelash. Within its first year of life, it develops something known as regional endothermy – the ability to regulate its body temperature. An Atlantic bluefin gets oxygen from cold ocean water using its gills, this process cools its blood. Then, heat the tuna generates swimming and hunting warms the blood.

 

In most fishes, this heat would be lost back out into the ocean through the gills. But in the Atlantic bluefin, a mechanism called countercurrent exchange traps the heat. Cold blood on its way to the large swimming muscles, passes close to warm blood leaving those muscles, in a specialized network of blood vessels known as a rete mirabile. Here the heat “jumps” to the cold blood and stays in the body.

 

This makes bluefin one of the few warm-blooded fishes, a huge advantage in the marine environment. Cold-blooded animals whose body temperature depends entirely on the environment become sluggish in colder waters. But a bluefin’s ability to keep warm means it has sharper vision, can better process information, and can swim faster than its prey.

 

It thrives in cold, deep, subarctic water. Thanks to their warm bloodedness, their powerful muscles, and their streamlined torpedo shape with fins that fold into grooves to reduce drag, bluefin tuna can reach speeds few other animals can match. Their maximum speed of 40 miles per hour is faster than that of a great white shark or orca whale, and even at their comfortable cruising speed, they can cross the Atlantic in a couple months.

 

All this swimming requires a great deal of oxygen, but the bluefin is adapted for this as well. The faster it swims, the more water passes over its gills, and the more oxygen it can absorb from that water.

 

This need for a constant flow of water means the tuna must always remain on the move. It also means bluefin cannot suck prey into their mouths the way most other fishes do. Instead, they must chase down their prey with their mouths open. They eat smaller prey than most predators their size, including squid, crustaceans, and smaller fish species like mackerel.

 

The bluefin’s temperature-regulating ability doesn’t just make it a superior hunter – it gives it nearly unlimited range. As soon as they’re strong enough to swim against the current, Atlantic bluefin leave the warm waters of their spawning grounds and spend their lives hunting all over the Atlantic Ocean.

 

Tunas from both the Gulf of Mexico and the Mediterranean Sea frequent the same feeding grounds and range from Brazil and Texas to Iceland and Senegal and beyond. But when the time comes to reproduce around age 10, they always return to their sea of origin. Here, groups of males and females release millions of eggs and sperm into the water. They’ll migrate back and forth between feeding and spawning grounds annually for the rest of their lives.

 

Atlantic bluefin can live for over 40 years, growing all the while. The largest specimens are tens of millions of times heavier than when they hatched. The same huge size that makes bluefin tuna indomitable in the ocean has made them vulnerable to one predator in particular: us.

 

Humans have a long history of fishing Atlantic bluefin – it’s even stamped on ancient Greek coins. But in recent decades, demand has skyrocketed as bluefin are hunted for sashimi, sushi, and tuna steaks. An individual fish can sell for $10,000 or more, promoting overfishing and illegal fishing.

 

But if recent conservation efforts are redoubled and quotas are better enforced, bluefin populations can begin to recover.

 

WORD BANK:

swallow /ˈswɒl.əʊ/ [B2] (v): nuốt

prey /preɪ/ [C2] (n): con mồi

killer whale /ˈkɪl.ə ˌweɪl/ (n): cá voi sát thủ

Atlantic bluefin tuna /ətˈlæn.tɪk ˌbluː.fɪn ˈtʃuː.nə/ (n): cá ngừ vây xanh Đại Tây Dương

adaptation /ˌæd.əpˈteɪ.ʃən/ [C1] (n): thích nghi

dominant /ˈdɒm.ɪ.nənt/ [C1] (adj): vượt trội/nổi bật

predator /ˈpred.ə.tər/ [C1] (n): động vật săn mồi

hatchling /ˈhætʃ.lɪŋ/ (n): mới sinh/mới nở

the Gulf of Mexico /ˌɡʌlf əv ˈmek.sɪ.kəʊ/ (n): Vịnh Mexico

the Mediterranean Sea /ˌmed.ɪ.tərˈeɪ.ni.ən/ (n): Biển Địa Trung Hải

endothermic /ˌen.dəʊˈθɜː.mɪk/ (adj): hấp thụ nhiệt

regulate /ˈreɡ.jə.leɪt/ [C1] (v): điều hòa/điều chỉnh

gill /ɡɪl/ (n): mang cá

generate /ˈdʒen.ə.reɪt/ [B2] (n): tạo ra

mechanism /ˈmek.ə.nɪ.zəm/ [C1] (n): cơ chế

countercurrent exchange (n): trao đổi ngược dòng

muscle /ˈmʌs.əl/ [B2] (n): cơ băp

specialized /ˈspeʃ.əl.aɪzd/ (adj): chuyên dụng/chuyên môn

blood vessel /ˈblʌd ˌves.əl/ (n): mạch máu

rete mirabile (n): phức hợp động mạch và tĩnh mạch

marine environment /məˈriːn ɪnˈvaɪ.rən.mənt/ (n): môi trường biển

depend /dɪˈpend/ [B1] (v): phụ thuộc

entire /ɪnˈtaɪər/ [B2] (adj): hoàn toàn/toàn bộ

environment /ɪnˈvaɪ.rən.mənt/ [B1] (n): môi trường

sluggish /ˈslʌɡ.ɪʃ/ (adj): chậm chạp

thrive /θraɪv/ [C1] (v): phát triển/lớn lên

subarctic /sʌbˈɑːk.tɪk/ (adj): cận Bắc Cực

torpedo /tɔːˈpiː.dəʊ/ (n): ngư lôi

fin /fɪn/ (n): vây

fold /fəʊld/ [B1] (v): gập lại

groove /ɡruːv/ (n): rãnh

drag /dræɡ/ (n): lực cản

orca whale /ˈɔː.kə/ (n): cá voi sát thủ

cruising speed /ˈkruː.zɪŋ ˌspiːd/ (n): tốc độ

absorb /əbˈzɔːb/ [B2] (v): hấp thụ

constant /ˈkɒn.stənt/ [B2] (adj): liên tục/thường xuyên

suck /sʌk/ [C2] (v): hút (bằng miệng)

crustacean /krʌsˈteɪ.ʃən/ (n): loài giáp xác

mackerel /ˈmæk.rəl/ (n): cá thu

superior /suːˈpɪə.ri.ər/ [C1] (adj): xuất sắc/vượt trội

unlimited /ʌnˈlɪm.ɪ.tɪd/ [B2] (adj): không giới hạn

the current /ˈkʌr.ənt/ (n): dòng chảy/dòng hải lưu

spawning ground /ˈspɔː.nɪŋ ˌɡraʊnd/ (n): nơi sinh đẻ/nơi sinh ra

Atlantic Ocean /ətˈlæn.tɪk/ (n): Biển Đại Tây Dương

reproduce /ˌriː.prəˈdʒuːs/ [C2] (v): sinh sản

origin /ˈɒr.ɪ.dʒɪn/ [B2] (n): nguồn gốc/nơi sinh ra

release /rɪˈliːs/ [C1] (v): thả ra

sperm /spɜːm/ (n): tinh trùng

migrate /maɪˈɡreɪt/ (v): di cư

specimen /ˈspes.ə.mɪn/ [C2] (n): con mẫu/mẫu vật

indomitable /ɪnˈdɒm.ɪ.tə.bəl/ (adj): không thể bị chế ngự/khuất phục

vulnerable /ˈvʌl.nər.ə.bəl/ [C2] (adj): dễ bị tấn công/dễ tổn thương

stamp /stæmp/ [B2] (v): đóng dấu

skyrocket /ˈskaɪˌrɒk.ɪt/ (v): tăng vọt

individual /ˌɪn.dɪˈvɪdʒ.u.əl/ [B2] (n): cá thể

promote [B2] (v): thúc đẩy

overfishing /ˌəʊ.vəˈfɪʃ.ɪŋ/ (n): khai thác (đánh bắt) cá quá mức

illegal /ɪˈliː.ɡəl/ [B2] (adj): bất hợp pháp

conservation /ˌkɒn.səˈveɪ.ʃən/ [B2] (n): bảo tồn

effort /ˈef.ət/ [C2] (n): nỗ lực

redouble /ˌriːˈdʌb.əl/ (v): tăng cường

quota /ˈkwəʊ.tə/ (n): hạn ngạch

enforce /ɪnˈfɔːs/ [C1] (v): thực thi


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