The study, published today in the journal PLOS Biology shows that the average body size and number of sharks and other marine predators—vital to maintaining healthy ocean ecosystems—fell significantly near cities with more than 10,000 people and associated fishing boats.

The minimum distance from people and fishing which had no measurable effect was 1,250 kilometers. This is far further than previous studies have suggested and probably reflects the increased distances fishing boats can now travel. As a result, sharks were only observed at 12% of sites monitored.

Lead author Dr. Tom Letessier said, ''Human activity is now the biggest influence on sharks' distribution. Just 13% of the world's oceans can be considered 'wilderness' but sharks and other predators are much more common and significantly larger at distances greater than 1,250 kilometers from people. This suggests that large marine predators are generally unable to thrive near to people and is another clear example of the impact of human overuse on our seas. ''

To collect their data, the team analyzed videos taken at 1,041 sites across the Indian and Pacific Oceans, selected to test the biggest possible range of conditions and habitats. Sharks and other free-swimming predators were studied using cameras attached cannisters(炮筒)filled with bait. In total, the team recorded 23,200 animals representing 109 species. These included 841 individual sharks from 19 different species.

Dr. Letessier added, ''Our study also found that shallower water environment, of depths less than 500 meters, were vital for marine predator diversity. We therefore need to identify sites that are both shallow and remote and protect them. However, there are still numerous shallow hot spots near human markets that are not appropriately protected, and this must change. ''

On December 26, 2004, an earthquake along the Indian Ocean caused a huge tsunami (海啸) that killed thousands of people in Asia and East Africa. However, wildlife officials at Sri Lanka's Yala National Park reported no mass animal deaths. Yala National Park is home to hundreds of wild animals.

Some researchers believe the animals at the park were able to sense the earthquake and moved to higher ground before the earthquake hit. Animals have good senses that help protect themselves from being hunted by their natural enemies. It is thought that their senses might also help them sense the coming disasters. Several countries have done research on the prediction (预测) of earthquakes by animals. There are two theories about how animals may be able to sense earthquakes. One theory is that animals sense the earth's shake. The other is that they can sense changes in the air. However, so far there has been no strong evidence about how animals may be able to sense earthquakes.

Other researchers are skeptical (怀疑) about using animals for earthquake predictions. The United States Geological Survey (USGS) officially states, "Changes in animal behaviors cannot be used to predict earthquakes. Even though there have been many cases of unusual animal behaviors before earthquakes, a connection between a specific behavior and an earthquake has not been made. Because of their fine senses, animals can often feel the earthquake at its earliest stages before the humans. That's why people say that the animal knew the earthquake was coming. But animals can also change their behaviors for many other reasons. If an earthquake can shake millions of people, it is likely that a few of their pets will, by chance, be acting strangely before the earthquake.”

Although scientists disagree on whether animal behaviors can be used to predict earthquakes, they all agree that it is possible for animals to sense changes in the environment before humans. Researchers around the world are continuing to study the connection between animal behaviors and earthquakes. It is hoped that these studies will help to predict earthquakes.

The average chicken will live for anywhere from three to seven years. That is mostly because there are so many different kinds of chickens living under a wide range of conditions.

In humans’ ongoing exploration to satisfy our desires for chicken noodle soup, wings, and legs, scientists have had to re-engineer the food chicken. In just 70 years, we’ve managed to build a brand-new chicken. It’s a bird with feet that never leave the ground, wings that scarcely shake, and stomaches that only grow bigger. It’s the hybrid ( 杂 交的) hen — perhaps the world’s first purpose-built animal.

As a result, the modern broiler chicken has a life expectancy of around seven weeks. Because that’s about when we like to eat them. Egg-laying chickens have similarly shortened lives. In contrast, what’s known as a heritage hen is similar to the chicken your grandmother may have had. They’re often kept in backyards, where there isn’t such an urgency to maximize egg production. Nature alone influences their genes, and thus heritage hens can live about eight years.

Although the variety is a pretty crucial factor, there is another issue that affects how long a chicken will live. Chickens get diseases, too. For instance, fowl cholera (禽霍乱) goes mostly for a chicken’s organs and joints. It can bring about sudden death in affected birds. Hens don’t have to stress out quite so much, as the disease is known to affect roosters more often than hens. Another life-shortening disease is salmonellosis (沙门氏菌病), a bacterial disease affecting young chickens. In itself, it may not directly kill a chicken. But since humans are sensitive to salmonella-infected meat and eggs, an outbreak could result in a massive killing at its source.

There are a lot of people trying to keep chickens safe. Additives in food, particularly those that strengthen the immune system, and vaccinations may play an important role in keeping a chicken around longer. But it’s also important to keep a chicken healthy, happy, and sheltered.