为什么海牛的数量会受到威胁

为什么海牛的数量会受到威胁

Manatees have long struggled to coexist with humans, and today all three manatee species are listed as vulnerable by the International Union for Conservation of Nature (IUCN). That means they aren't officially endangered, which is one category closer to extinction, but it doesn't mean they're out of danger. The West Indian manatee, the Amazonian manatee, and the African manatee each still faces "a high risk of extinction in the wild in the immediate future," according to the IUCN. Of the three, only the West Indian manatee is split into subspecies, and both of those — the Florida manatee and Caribbean manatee — are listed as endangered.

长期以来，海牛一直在努力与人类共存，如今，国际自然保护联盟(IUCN)已将这三种海牛列为濒危物种。虽然它们没有被正式列为濒临灭绝的物种，但这并不意味着它们脱离了危险。根据世界自然保护联盟的说法，西印度海牛、亚马逊海牛和非洲海牛在不久的将来仍然面临着“灭绝的高风险”。在这三种海牛中，只有西印度海牛被划分为亚种，佛罗里达海牛和加勒比海牛都被列为濒危物种。

Florida manatees, a subspecies of West Indian manatee, are commonly injured by collisions with boats.Robert Bonde / U.S. Geological Survey / Flickr / Public Domain

There are still a few thousand individuals in each manatee species, but their population estimates are often hindered by scant data, and even the best-case scenarios don't provide much buffer from the threats they face. There are thought to be fewer than 15,000 African manatees, according to The Zoological Society of London (ZSL), while the Amazonian manatee numbers anywhere from 8,000 to 30,000. The Florida manatee fell as low as a few hundred individuals in the 1970s, when it was added to the U.S. endangered species list, but conservation efforts have since helped it rebound to about 6,600, according to the U.S. Fish and Wildlife Service (FWS). That led the FWS to downgrade Florida manatees from endangered to threatened in 2017, despite objections from many conservationists who argue the move was premature. Less is known about the Caribbean subspecies, but its population is thought to be smaller and sparser.

每一种海牛仍有几千只，但它们的数量估计往往受到缺乏数据的阻碍，而且即使是最乐观的情况也不能为它们面临的威胁提供多少缓冲。据伦敦动物学会(ZSL)称，非洲海牛的数量不足15000头，而亚马逊海牛的数量在8000到30000头之间。上世纪70年代，佛罗里达海牛的数量下降到只有几百头，当时它被列入美国濒危物种名单，但根据美国鱼类和野生动物管理局(FWS)的数据，自那以后，保护努力帮助它回升到大约6600头。这导致鱼类和野生动物管理局在2017年将佛罗里达海牛从濒危物种降级为濒危物种，尽管许多自然资源保护人士反对，认为此举为时过早。人们对加勒比亚种的了解较少，但它的种群被认为更小更稀少。

Before manatees were widely known, sailors sometimes mistook the mammals for mermaids. David Hinkel / U.S. Fish and Wildlife Service / Flickr / CC BY-2.0

Threats to Manatees

海牛面临的威胁

Manatees are in danger from people virtually everywhere they live, but the risks can vary widely depending on the species and location. Here's a closer look at the major threats humans pose to manatees.

海牛几乎在它们生活的任何地方都面临着人类的威胁，但根据物种和地点的不同，风险也会有很大的不同。以下是人类对海牛的主要威胁。

Boats

船

Humans have a history of hunting manatees, but today, manatees are more threatened by human ignorance and carelessness than deliberate predation. People commonly wound and kill manatees by operating motorized watercraft in their habitats. This problem is most severe for West Indian manatees, particularly Florida manatees living in densely populated coastal areas.

人类有捕猎海牛的历史，但是今天，海牛受到的威胁更多的是人类的无知和粗心，而不是蓄意的捕食。人们通常在海牛的栖息地使用机动船只伤害或杀死它们。这个问题对西印度海牛最为严重，尤其是居住在人口密集的沿海地区的佛罗里达海牛。

Fishing Gear

渔具

As with many marine mammals, entanglement in fishing lines and nets poses another grave threat to manatees. Although people do target manatees in some places with traps, nets, and baited hooks, they are also widely killed by fishing gear intended for other animals. This can happen to both adults and juveniles, and unless humans find them in time to help, entangled manatees generally have slim chances of survival. Many drown, and those who manage to surface for air may still be unable to move around easily enough to survive for very long.

和许多海洋哺乳动物一样，被鱼线和渔网缠住对海牛构成另一个严重威胁。虽然人们在一些地方会用陷阱、网和带饵的鱼钩瞄准海牛，但它们也会被用于其他动物的渔具杀死。这种情况可能发生在成年和幼年海牛身上，除非人类及时找到它们来帮助它们，否则被缠住的海牛通常存活的机会很小。许多海牛溺水而亡，那些设法浮上水面呼吸空气的海牛可能仍然无法轻易地四处走动，无法存活很长时间。

Habitat Loss

栖息地的丧失

Loss of habitat has become one of the most pervasive threats to endangered species around the world, and manatees are no exception. In Florida, rapid human population growth has led to widespread coastal development near estuaries and coastal wetlands, often at the expense of vital seagrass beds and warm-water springs. Tampa Bay, for example, lost about 80% of its seagrass between 1900 and 1980, largely due to poor water quality.

栖息地的丧失已经成为世界各地濒危物种面临的最普遍威胁之一，海牛也不例外。在佛罗里达州，人口的快速增长导致了河口和沿海湿地附近广泛的沿海开发，往往以牺牲重要的海草床和温泉水为代价。例如，坦帕湾在1900年到1980年间损失了大约80%的海草，主要是由于水质差。

One of the easiest ways to help manatees is to give them space and obey boating regulations. Jim Reid / U.S. Fish and Wildlife Service / Flickr / CC BY-2.0

Illegal Hunting

非法捕猎

Many manatee populations still haven't recovered from intensive hunting by humans in the past, leaving them more vulnerable to modern threats like boats, habitat loss, and even smaller-scale local hunting. All three species are now legally protected, but those laws are not always enforced, and illegal manatee hunting remains common in Africa and especially South America. In fact, the IUCN cites illegal hunting as the No. 1 threat for manatees in the Amazon, where hunters typically catch the animals with harpoons, then sell their meat and other parts for local consumption.

许多海牛的数量还没有从过去人类的密集捕猎中恢复过来，这使得它们在现代的威胁中更加脆弱，比如船只、栖息地的丧失，甚至是小规模的本地捕猎。这三种海牛现在都受到了法律的保护，但这些法律并不总是被执行，非法捕猎海牛在非洲，尤其是南美仍然很常见。事实上，国际自然保护联盟(IUCN)将非法狩猎列为亚马逊地区海牛的头号威胁。在那里，捕猎者通常用鱼叉捕获海牛，然后将其肉和其他部分出售给当地居民食用。