Zoologists track animals using global-positioning-system(GPS)tags(标签) which then return their data via satellite. Marine(海洋的)biologists have a harder time of it, though, because radio signals can’t pass through seawater. This makes it impossible either to receive GPS signals or to send any data collected back to base.

That does not stop people tagging sea creatures. Data collected and stored in a tag can be sent to a satellite in bursts if the species in question is one that comes to the surface from time to time. A tag may also be recovered if the animal carrying it is caught by a fishing boat. Fisherfolk are typically paid a few hundred dollars per tag returned to its home laboratory.

None of these methods, though, keeps accurate track of where the animal carrying the tag has been. For these and other reasons, it would therefore be useful to have a marine equivalent of GPS. And one is now being employed. The Woods Hole Oceanographic Institution, in Massachusetts, hopes to fill the seas with sonic beacons(声波信标) that will play the role of GPS satellites.

The sea is divided into distinct layers that have different temperatures. During the Second World War, American scientists showed that some of these layers act as sonic waveguides. They called them “sound fixing and ranging” (sofar) channels. Sound sent out in one of these channels echoes(回响) between the layers above and below, thus staying in the channel. Thus constrained(被约束)，a sound wave can travel hundreds of kilometers before it becomes too weak to detect.

The sofar transmitters from Woods Hole are usually at an appropriate depth for the channel concerned. Every 12 hours they broadcast a 32-second-long location signal known as a pong. Pongs are so called because they are similar to sonar “pings”, but of lower frequency. In typical conditions a pong can be picked up 1,000 km away. By listening to the pongs from several beacons a receiver can calculate its location. Existing receivers for the two sofar transmitters are currently carried on free-floating instrument packs. But the plan is to have two more transmitters this year, and more in future years.

In order to learn about advanced scientific technology and ideas for fighting against desertification (沙漠化), Rezaali Pakzad left Iran to study in Northwest China’s Gansu province. He is a 27-year-old doctoral student at Lanzhou University, focusing on soil desertification control.

In his view, Iran, like many countries, faces environmental problems such as desertification. When he did field surveys and research in Minqin county, Gansu, he found that the local desertification characteristics were very similar to those of his hometown. “Minqin is between two deserts. From being ‘about to disappear’to being gradually green, the scientific and effective prevention and control methods of the Chinese government have greatly changed the county, and made me see the hope of improving the ecology in my hometown,” he says.

He believes that China has certainly contributed to the global effort to combat desertification, and that the Chinese contribution is worth learning from. Through in-depth research in recent years, he has learned a lot about China’s new technologies and new ideas for combating desertification.

China has developed advanced technology models, which have introduced more green to deserts. Already among the top nations in the world in the field of combating desertification, China has shared its experience with other countries, carried out international consociation, and contributed to global desertification control.

Rezaali also believes he has made progress during his five years of living and studying in China. He hopes to achieve a lot, at a high level, in his research field and to contribute to international exchanges and cooperation in desertification control. “I want to be an ‘ecological messenger’ by spreading green ideas,” he says.

Finding fish is going to get harder as climate change continues to heat the world’s oceans. A new study finds that warming seas over the past 80 years have reduced the sustainable catch of 124 species of fish and shellfish. Sustainable catch refers to the amount that can be harvested without doing long-term damage to the health of populations of some species.

Overfishing has made that decline worse, researchers say. Overfishing refers to catching so many fish that the size of the population falls. In some parts of the world, such as the heavily fished Sea of Japan, the decrease is as high as 35 percent. That’s a loss of more than one in every three fish.

Researchers examined changes in 235 populations of fish and shellfish between 1930 and 2010. Those fish populations spread far apart across 38 ocean regions. Temperature changes vary from one ocean site to another. But on average over that time, Earth’s sea-surface temperatures have risen by about half a degree Celsius.

On average, that warming has caused the sustainable catch to drop by 4.1 percent, the study found. About 8 percent of the fish and shellfish populations the team studied saw losses as a result of the ocean warming. However, about 4 percent of some populations increased. That’s because certain species have thrived in warmer waters. One example is a kind of black sea fish. It lives along the northeastern U.S. coast. As warming continues, these fish will reproduce faster until they reach their limit.

About 3.2 billion people worldwide rely on seafood as a source of food. That means it’s urgent for commercial fishing fleets and regulators to consider how climate change is affecting the health of all of those fish in the sea.