The Census of Marine Life - IELTS Listening Answers & Explanations

Host: "How many fish in the sea?" is a hot topic for many scientists. Today we have invited a famous scientist who spent 10 years in studying marine life to give us an introduction of the latest survey called "The Census of Marine Life". Let's welcome Alok Jha.

Alok: Thanks Ella. The Census of Marine Life has been the biggest and most comprehensive attempt ever to answer that question—how many fish are there in the world's oceans? The Census of Marine Life, which hopes to indicate a baseline of marine life, estimates that there are more than 230,000 species in the seas. The study covers from coast to the open ocean, from the shallows to the deeps, from little things like microbes to large things such as fish and whales. Our team of over 360 scientists from all over the world have spent the past ten years surveying 25 regions, from the Antarctic through the temperate and tropical seas to the Arctic to count the different types of plants and animals. The findings indicate that crustacean such as lobsters, crabs, krill and barnacles accounts for a fifth of the number of species in the world's oceans and half of the world's marine species is mollusc (squid and octopus) and fish (including sharks). The charismatic species usually used in propagating environmental protection for example whales, sea lions, turtles and sea birds account for less than 2% of the species in the world's oceans. The study has also focused on major fields of concern for conservationists. In every region, they got the same experience of a major collapse of what we were usually very abundant fish stocks or crabs or crustaceans that are now only 5-10% of what they used to be. The main reasons include overfishing, degraded habitats, and pollution. But more problems are presented: rising water temperatures and acidification brought by climate change and the growth in areas of the ocean that are low in oxygen and, therefore unable to support marine life. The Census of Marine Life shows that enclosed seas such as the Mediterranean Sea, Gulf of Mexico, China's shelves, Baltic, and the Caribbean have the most threatened biodiversity. The pollutions in enclosed seas are mainly from chemicals or garbage that people throw into it. Dense coastal populations of humans also tend to be packed along enclosed seas, meaning rising contaminations and extraction of more biodiversity from the water.

The Mediterranean Sea, which contains around 17,000 identified species, has been a region with high threat. Scientists in our team studying the Mediterranean identified problems related to increased litter from shipping and munitions across the sea as well as bombs discharged during the Kosovo war. The Mediterranean also has to face problems with invasive species displacing the creatures that already live there. The Census of Marine Life shows that the Mediterranean Sea has the most alien species—more than 600 among all the 25 regions that have been surveyed. It looks like that the region with coral reefs has always had a very high rate of speciation. It also has a very diverse range of habitats from the deepest regions of the oceans to large regions of shallow seas, which can afford coral reefs.

The most diverse regions identified by The Census of Marine Life are around Australian and Japanese waters which contain more than 30,000 species each and are among the most biologically diverse in the world. Next in line are the oceans off China, the Mediterranean sea and the gulf of Mexico. Besides algae and the seabirds and mammals that travel around the sea viperfish has been regarded as the most "cosmopolitan" marine creature by The Census of Marine Life. Its presence was recorded in around a quarter of the world's seas.

And for every marine species of all kinds known to science, scientists of The Census of Marine Life estimate that at least four have yet to be discovered. For example, about 70% of species of fish have been discovered but for most other groups likely less than one-third are known. Our research team has found the number of marine fish species was about 16,764, and was growing at around 100 a year. So scientists estimate that there are almost 22,000 fish species in the world's oceans. The most fruitful potential areas for discovery include the tropics, deep seas and southern hemisphere. Although most ocean organisms still remain nameless and their numbers unknown at the end of The Census of Marine Life, we still gained an important and exciting start.

Host: Definitely. That's a great achievement.

Alok: Thank you very much.

Host: OK. Thanks to Alok for giving us the amazing information about marine life. Next week we will (fade)...