Sharks are the world’s most frightening and impressive fish. They are believed to have been in existence before the dinosaurs. In fact, scientists guess that the earliest shark species were swimming in the earth’s waters some 420 million years ago.

The shark species are different in terms of their physical appearance, diets and habits. Different shark species prefer different waters, but, generally, sharks are found all over the world. They live anywhere between relatively shallow depths and about 2,000 meters from the surface.

The shark’s body is streamlined (流线型的) to allow these effective hunters to slide through the water smoothly. Sharks that swim around on the ocean floor usually have flat bodies, allowing them to slide across the sand unnoticed. Unlike other fish, which have both bones and cartilage (软骨), sharks only have cartilage, increasing their flexibility and decreasing their weight to allow even faster movement. Their replaceable rows of teeth are used only for catching their prey (猎物) and tearing off large pieces of flesh. They do not chew their food, but swallow it whole.

All sharks are meat eaters. However, their diets are varied. Sharks are believed to be relatively intelligent.

There have been several shark attacks on people, usually resulting in severe injuries or death. The bull shark is the most common killer for bathers, as it swims in the shallow waters. To avoid attacks by such sharks, it is necessary for bathers to stay within the swimming confines (界限) set by lifeguards and for bathers to get out of the water immediately if they have a bleeding injury.

Sharks continue to be threatened by hunting and pollution, yet remain one of the most fascinating (迷人的) creatures.

Between July and December 2021, more than 11 million young oysters (牡蛎) were put into the Hudson River. They are part of a plan to create a healthier ecosystem in the river by increasing the oyster population.

The waters used to be full of oysters, which were collected for food and shells too much. Weather got warmer and New York City also dumped waste water and harmful chemicals into the river. By 1927, most of the oysters had died. Now, oysters may help to restore the waters and bring back marine life. How do oysters do it?

Oysters help clean water. They are filter feeders, taking in water through their gills (鳃) and filter out the food they eat, such as plankton (浮游生物) and algae (海藻). A single adult oyster can filter up to 189 litres of water in a day. They also filter other harmful things out of the water, one of which is nitrogen, a chemical often found in fertilizers (肥料). Sometimes nitrogen gets washed into rivers and oceans when it rains. Too much nitrogen in the water causes large amounts of algae to grow. The algae use up the oxygen in the water, harming other marine life. Oysters filter nitrogen out of the water and use it to grow their shells.

Oysters also build reefs, benefiting the whole ecosystem. Oysters attach themselves to hard surfaces underwater like rocks. Then more oysters attach themselves on top of those, and more on top of those. As the oysters grow, their shells combine together to form a reef. Oyster reefs provide homes for plants and animals, thus creating more biodiversity. Reefs also serve to protect the shoreline. Large reefs weaken the shock of waves coming in from the ocean, and help lessen flood disaster and prevent gradual destruction of the coast.

It will take decades before the new reefs grow as big as the reefs destroyed long ago, but signs show up that the ecosystem is getting healthier.

“You’re as stupid as a goat.” It is a common insult (侮辱) in Nigeria. Recently a study published in Animal Behaviour suggested that’s just not true.

Alan McElligott, associate professor of animal behavior and welfare in City University of Hong Kong conducted a study in cooperation with Marianne Mason, an expert in the cognitive (认知的) abilities of goats in England.

In the experiment, a speaker was hidden to play a recording of a human saying “Hey, look over here!” with two versions—a happy one and an angry one. When the study’s 27 goat participants entered the pen one by one, the speaker would play either the positive or negative version 9 times in a row. At first the goats would respond by looking up and even looking for the source of the sound. But after a few repetitions, they would just stop paying attention. Then the speaker switched to play the opposite version three times. 71% of those disinterested goats lifted their ears and looked up in the direction of the sound. Among those newly engaged goats, some started to investigate the source of the sound longer than in the initial stages of the experiment, suggesting they noticed the emotions had changed.

The finding is a case in point of the intelligence of goats. Actually, experienced goat farmers have already known that their livestock (家畜) are discriminating listeners and respond well to kind treatment. So why do such a study if that’s already known? “By showing this ability in goats, we’re trying to move the needle in terms of opening people’s eyes to the cognitive abilities of livestocks. Our overall goal is to get people to think about animals in a different way, to treat them a little bit better.” says Mason. The two researchers hope that people will start to understand these livestocks deserve to be nicely treated, especially as we are using them for our milk products and meat.