Читать книгу Fundamentals of Conservation Biology - Malcolm L. Hunter Jr. - Страница 23

The year is 1960. On the island of Española, a low dry expanse of eroding lava far to the southeast in the Galápagos Archipelago, a giant tortoise rests under a bush and gazes out to sea. The edges of her shell flare out dramatically – a distinctive characteristic of her lineage – but lichens cover it, a sign that she has not met with and bred with another tortoise in decades. Moreover, her head lies weakly on her outstretched forelimbs, her body withering within her shell. Beyond the small bush sheltering her from the blazing sun, hooves of goats thud against rock and dust swirls. Kids bleat hungrily after their mothers. The island is devastated, and even the goats are starving, driven to eat seaweed and drink seawater. The magnificent stands of arboreal cactus that once crowned the island are gone, torn down and stripped of their pads. Gone also is the carpet of fragile herbs and grasses that once covered the island, species that the large tortoises with their soft elephant‐like feet and simple “beak” could only graze, but the toothed and hooved goats could destroy. Even the finches and mockingbirds that flitted about noisily in search of seeds and insects on the leaves of shrubs have mostly disappeared. Little remains but patches of prickly mesquite and expanses of exposed, powdery earth, from which lava blocks protrude polished brightly by the shells and claws of thousands of generations of giant tortoises. But they too are now all gone. Seemingly only the old female tortoise remains.

By the 1950s the Española Island tortoise had been given up as extinct. The island was low and accessible and the first stop for many whaling ships visiting the Galápagos in the 1800s. These sailing ships disgorged hungry sailors, who wobbled on their unstable “sea legs” deep into the trackless island, smoking clay pipes and clutching precious water supplies in fragile, hand‐blown glass bottles. After much searching these sailors would haul tortoises down to the shore, likely thousands of them. Back on their ships the sailors stored the tortoises below decks where they survived for up to a year, without food or water, waiting to be slaughtered one by one to provide occasional fresh meat for the often scurvy‐ridden crew. After decades of such depredations even the whaling ships stopped visiting Española once word got around that there were “no more” tortoises. Introduction of goats to the island (presumably to supply another source of meat for future visits) made matters even worse. By the 1950s boats passing the island reported the enormous goat population and wasted landscape, apparently confirming the demise of the Española Island tortoise.

One person, however, held out hope. In 1959 Miguel Castro was appointed as the first tortoise warden for the newly formed Galápagos National Park, which brought the first protections to these largely abandoned islands. He had a tough task ahead of him: starting the first program to protect these magnificent reptiles, which had been subject to plunder for two centuries and remained mere sources of bush meat for most local people, themselves scratching a living out of this austere landscape. Castro sailed a small boat to Española and made a brief reconnaissance trip in August 1963. Perhaps some tortoises might still exist. After much wandering around he found a single tortoise eating a torn‐down cactus in the company of 15 goats. If there was one, perhaps there might be more? His curiosity piqued, Castro made a second trip in November 1963. Again he saw mostly goats, thousands of them, busily stripping bark from cactus tree roots, causing the cacti to fall over. Remarkably he also found the same tortoise he had found in August. He then found another tortoise, in a different part of the island, living in isolation. The signs were positive that perhaps a small nucleus of tortoises might survive.

Further trips to Española located more individuals. Some 14 were eventually relocated and brought into captivity near Park headquarters on another island. Once together in captivity, mating quickly ensued among the tortoises, who were now enjoying abundant food compared to life on their goat‐devastated island, perhaps the first breeding to occur in a half century!

But producing young tortoises was not easy. Nobody had successfully bred giant tortoises in large numbers before. Even the best zoos of Europe and the United States had tried and failed. Conventional wisdom was that it was not possible. Through trial and error, another park guard, Fausto Llerana, along with many helpers and advisors, gradually developed tortoise husbandry.

One lingering problem was that the small nucleus of remaining adults had a very skewed sex ratio: 12 females and just two males. So the international search for more Española tortoises began. Old records were unclear but suggested that a group of tortoises had been removed from Española and shipped to San Diego, California, around 1935. Perhaps some yet survived 35 years later in distant California? Further investigation revealed that there was indeed a male still alive from that shipment. So‐called “Diego” was large and still extremely vigorous. He was boxed up and after several false starts trying to find an aircraft suitable to transport him, he was finally flown to Ecuador and then sailed back to Galápagos in August, 1977. The captive population became strikingly more productive shortly after Diego’s arrival. Diego is to this day a prolific breeder.

The captive Española tortoises also had a major, unanticipated and ancillary benefit – educational and public relations value. Local people, especially school children, and tourists visited (and still do) the rearing center with its breeding enclosures and incubators. Visitors can still see the hatchlings clustered around their water baths. The breeding program came to serve as a prime example of what could be done to reclaim some of what had been lost in Galápagos. It remains a major attraction to visitors.

Once numbers in captivity had built up and the Española tortoises were out of danger of outright extinction, the Galápagos National Park Service turned its attentions to remedying the problems on the tortoises’ home turf back on Española. During the 1970s, about 3000 goats were eliminated from Española through an intense hunting campaign by park guards. Groups of guards with rifles, stout boots, and jugs of water would go to the field for weeks and even months and hunt down the goats. The terrain was difficult and the comforts few. They lived largely off what they hunted. Huge numbers of goats were culled early in the process but the very last goats took many months to eliminate. The last goats were of course the wiliest ones of all; the hunters knew each by their coat colors. The guards eventually succeeded, through sheer dedication and skill. Now just a few skulls of goats and dessicated goat droppings can be found on the island, weathering to bright white in the blazing sun

After the goats were removed the repatriations of the first hatchling tortoises began in 1975. Areas of the island with the last remaining patches of cactus were chosen as special release sites because the cactus provides critical food, moisture, and shade for young tortoises. Boxes of 5‐year‐old hatchlings were transported first by sea and then up the rocky slopes of the islands in backpacks and released one by one.

The captive population generated over 2000 offspring repatriated to Española. Of the repatriated tortoises, perhaps half died of natural causes but half survived and grew well (Gibbs et al. 2014). Most significantly, after nearly 30 years of reintroductions, some of the first repatriates have grown to adulthood. These repatriated tortoises are now reproducing on Española (Fig. 1.6). Nests can be found and occasionally, a soft‐shelled, tiny tortoise newly emerged from its nest.

Figure 1.6 This Española tortoise was among the very first repatriated to the island as a small hatchling some 25–30 years ago once goats had been removed and the island’s habitat restored. It is likely one of the tortoises now responsible for the new hatchlings appearing again on the island, representing the first reproduction in this population in many decades. At right is Mr Fausto Llerena, a park guard and tortoise keeper of over 40 years, who largely is responsible for figuring out how to breed Galapagos tortoises in large numbers in captivity.

(James P. Gibbs, author)

The population is again secure and sustaining itself. But not all is well. The vegetation has recuperated rapidly now that the goats are gone, but perhaps too rapidly as it has become impenetrable in many areas, even blocking movements by the newly arrived tortoises. The slow‐growing cacti remain scattered and rare but they are showing signs of recovery, now that the tortoises are back to disperse their seeds.