為什么海牛的數(shù)量會(huì)受到威脅

為什么海牛的數(shù)量會(huì)受到威脅

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.

長(zhǎng)期以來(lái)，海牛一直在努力與人類共存，如今，國(guó)際自然保護(hù)聯(lián)盟(IUCN)已將這三種海牛列為瀕危物種。雖然它們沒(méi)有被正式列為瀕臨滅絕的物種，但這并不意味著它們脫離了危險(xiǎn)。根據(jù)世界自然保護(hù)聯(lián)盟的說(shuō)法，西印度海牛、亞馬遜海牛和非洲海牛在不久的將來(lái)仍然面臨著“滅絕的高風(fēng)險(xiǎn)”。在這三種海牛中，只有西印度海牛被劃分為亞種，佛羅里達(dá)海牛和加勒比海牛都被列為瀕危物種。

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.

每一種海牛仍有幾千只，但它們的數(shù)量估計(jì)往往受到缺乏數(shù)據(jù)的阻礙，而且即使是最樂(lè)觀的情況也不能為它們面臨的威脅提供多少緩沖。據(jù)倫敦動(dòng)物學(xué)會(huì)(ZSL)稱，非洲海牛的數(shù)量不足15000頭，而亞馬遜海牛的數(shù)量在8000到30000頭之間。上世紀(jì)70年代，佛羅里達(dá)海牛的數(shù)量下降到只有幾百頭，當(dāng)時(shí)它被列入美國(guó)瀕危物種名單，但根據(jù)美國(guó)魚(yú)類和野生動(dòng)物管理局(FWS)的數(shù)據(jù)，自那以后，保護(hù)努力幫助它回升到大約6600頭。這導(dǎo)致魚(yú)類和野生動(dòng)物管理局在2017年將佛羅里達(dá)海牛從瀕危物種降級(jí)為瀕危物種，盡管許多自然資源保護(hù)人士反對(duì)，認(rèn)為此舉為時(shí)過(guò)早。人們對(duì)加勒比亞種的了解較少，但它的種群被認(rèn)為更小更稀少。

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

海牛面臨的威脅

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.

海牛幾乎在它們生活的任何地方都面臨著人類的威脅，但根據(jù)物種和地點(diǎn)的不同，風(fēng)險(xiǎn)也會(huì)有很大的不同。以下是人類對(duì)海牛的主要威脅。

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.

人類有捕獵海牛的歷史，但是今天，海牛受到的威脅更多的是人類的無(wú)知和粗心，而不是蓄意的捕食。人們通常在海牛的棲息地使用機(jī)動(dòng)船只傷害或殺死它們。這個(gè)問(wèn)題對(duì)西印度海牛最為嚴(yán)重，尤其是居住在人口密集的沿海地區(qū)的佛羅里達(dá)海牛。

Fishing Gear

漁具

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.

和許多海洋哺乳動(dòng)物一樣，被魚(yú)線和漁網(wǎng)纏住對(duì)海牛構(gòu)成另一個(gè)嚴(yán)重威脅。雖然人們?cè)谝恍┑胤綍?huì)用陷阱、網(wǎng)和帶餌的魚(yú)鉤瞄準(zhǔn)海牛，但它們也會(huì)被用于其他動(dòng)物的漁具殺死。這種情況可能發(fā)生在成年和幼年海牛身上，除非人類及時(shí)找到它們來(lái)幫助它們，否則被纏住的海牛通常存活的機(jī)會(huì)很小。許多海牛溺水而亡，那些設(shè)法浮上水面呼吸空氣的海牛可能仍然無(wú)法輕易地四處走動(dòng)，無(wú)法存活很長(zhǎng)時(shí)間。

Habitat Loss

棲息地的喪失

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.

棲息地的喪失已經(jīng)成為世界各地瀕危物種面臨的最普遍威脅之一，海牛也不例外。在佛羅里達(dá)州，人口的快速增長(zhǎng)導(dǎo)致了河口和沿海濕地附近廣泛的沿海開(kāi)發(fā)，往往以犧牲重要的海草床和溫泉水為代價(jià)。例如，坦帕灣在1900年到1980年間損失了大約80%的海草，主要是由于水質(zhì)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

非法捕獵

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.

許多海牛的數(shù)量還沒(méi)有從過(guò)去人類的密集捕獵中恢復(fù)過(guò)來(lái)，這使得它們?cè)诂F(xiàn)代的威脅中更加脆弱，比如船只、棲息地的喪失，甚至是小規(guī)模的本地捕獵。這三種海牛現(xiàn)在都受到了法律的保護(hù)，但這些法律并不總是被執(zhí)行，非法捕獵海牛在非洲，尤其是南美仍然很常見(jiàn)。事實(shí)上，國(guó)際自然保護(hù)聯(lián)盟(IUCN)將非法狩獵列為亞馬遜地區(qū)海牛的頭號(hào)威脅。在那里，捕獵者通常用魚(yú)叉捕獲海牛，然后將其肉和其他部分出售給當(dāng)?shù)鼐用袷秤谩?/p>