Some fish form huge schools. Could fish set up schools and teach their children how to survive in the ocean? You may ask. No. Here the “schools” are not the places where you study. They are fish shoals (鱼群) that cover tens of kilometers. What causes hundreds of millions of fish to gather and move together is one of biology’s mysteries.
Darkness appears to be the first step to the creation of shoals, according to a study published in the March 27 journal Science. A team of researchers from the Massachusetts Institute of Technology (MIT) and five other institutions studied Atlantic herring (鲱鱼), which forms shoals on a fishing ground off Massachusetts. They used an underwater imaging technology and fish-finding sonar (声纳) to observe the herring over several days in autumn when they spawn (产卵).
They found that, as the sun set, fish in scattered (分散的) groups began swimming much closer to one another than they normally do. When the number of fish reached a certain point in an area, this set off a chain reaction of similar behavior that spread like a sound wave through the water.
The herring’s movement seemed to be started by sunset. The team didn’t record the breakup of these shoals, but a previous study suggested that as the sun rose, the shoals fell apart.
“When the light fades (逐渐消失), it’s safer for the fish to move away from the seabed,” says Nicholas Makris, a professor at MIT who led the research. “Once they have a certain number of other fish, they suddenly come together - forming a shoal covering tens of kilometers within tens of minutes.”
Herring form shoals to migrate during the autumn spawning season. Some shoals were 40 km across and 30 m from top to bottom. They formed in deep water and moved into more shallow waters to spawn.
Forming shoals helps protect them from predators (掠食者) by giving them simple strength in numbers. The ordered movement of the shoal means the fish can reach their spawning ground more quickly and more safely.
Scientists have never before gathered information on so many animals acting together. Understanding these herring shoals could lead to more ideas about what causes animals to move in schools, says Iain Couzin, a biologist at Princeton University, US.
1. Which school in the following expressions is used the same way as the underlined one in the first paragraph?
A. schools of thoughts B. school a horse C. a school of whales D. a medical school
2. Which of the following statements is true?
A. There are more large shoals of herring at night than in the daytime.
B. The research on Atlantic herring was conducted independently by the Massachusetts Institute of Technology.
C. The larger the shoal of herring is, the more slowly it moves.
D. Scientists have found out the reason why fish gather and move together in huge shoals.
3. According to the research, herring tend to get together except ______.
A.when there are predators around B. when they spawn C. when the sun sets D. when the sun rises
4. What seems to be the main reason for herring to gather and move together?
A. To avoid the darkness.
B. To keep other kinds of fish out of their spawning ground.
C. To spawn in the shallow waters.
D. To make themselves feel safe.
的电流变化大于通过
的电流变化，所以根据
可得△U1＞△U2 ，A正确，向右滑动的过程中，总电流增大，所以通过
可得通过电阻R2的功率一定增大，C正确，因为
可得通过电阻R1的功率一直减小，B错误，根据公式
可得当R=r时电源的电功率最大，但是题中没有给出R和r的关系，所以D错误，