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Ecology

Survivors of El Niño

Warming of the waters of the Pacific puts the populations of fur seals off the coast of Peru in a critical situation

It is common to associate the disappearance of plants and animals with human action. But at least this time, the death en masse of fur seals from the coast of Peru and the north of Chile seems to be related to a natural phenomenon, El Niño, the increase in the temperature of the surface waters of the Pacific Ocean by as much as 11°C. In 1997 and 1998, the most intense El Niño of last century took to their death some 70% of Peru’s fur seals: of the 24,481 fur seals that used to live there, about 8,200 remained. And, of these, only 2,153 were adults and capable of generating descendants for the next generation – one male pup can take from six to eight years to begin to reproduce. The specialists regard 7 thousand animals of a reproductive age as the minimum figure that a population of vertebrates should have in order to guarantee the perpetuation of the species for 40 generations. The warning was given by a team of researchers from the Biosciences Institute of the University of São Paulo (USP) and the Sea Institute of Peru (Imarpe). “The reduced population of fur seals is a threat to the survival of the species and should be taken into consideration by the Peruvian government when proposing measures for protection and conservation”, says biologist João Morgante, head of the Evolutionary Biology and Conservation of Vertebrates Laboratory (Labec) of USP’s Biosciences Institute and the coordinator of a series of population studies about neotropical vertebrates.

Nor was it imagined that the fur seals of Peru and the north of Chile, which inhabit the waters of the Pacific, were different from the animals from other South American regions. In 2004, during her doctorate, biologist Larissa de Oliveira, from Rio Grande do Sul and connected with Labec and the Rio Grande do Sul Aquatic Mammals Study Group (Gemars), found that she was dealing with a new species, exclusive to these areas and distinct from the one found on the coast of Uruguay and Argentina, of the Atlantic Ocean. This discovery increases the concern with the extinction of these furry fatties that unlike seals, sit on their hind paws, and whose pointed muzzle is reminiscent of the wolf. Larissa proposes that the species of fur seals called Arctocephalus australis be considered only for the fur seals  of the Atlantic coast (Uruguay, Falkland Islands, or Malvinas, and Argentina), while the animals from the Pacific coast of South America (coast of Peru and north of Chile) could be looked at as another species, provisionally called Arctocephalus sp. A.

Skulls and DNA
Working under the orientation of Morgante and Erika Hingst-Zaher, from the Morphometry Laboratory of USP’s Zoology Museum, Larissa arrived at these conclusions after examining 594 skulls of adult males from Uruguay, Argentina, Chile, the Falkland Islands and from Peru, held in museums in America and in Europe. She used a series of measures by means of which the variations in the size and format of the skull are analyzed, availing herself of an as yet little disseminated method, geometric morphometry.

The 594 skulls of the fur seals were photographed from various angles and transformed into 1,027 digital images, which were given 62 points of reference. The analysis of the variation of these 63,674 points showed clearly the differences in the shape and in the size of the skulls of each of the populations of fur seals of South America. The biologist from Rio Grande do Sul then collated the data obtained with the results of the analysis of DNA fragments called microsatellites of 226 fur seals from Uruguay and from Peru, which reinforced the differences between these populations.

Besides the differences in the skull measurements and in the DNA, there are physical and behavioral variations between the fur seals from the two oceans that bathe South America, particularly between the populations of Uruguay and Peru. The animals that inhabit the Pacific have a larger skull, are heavier, longilineal, and have a narrower muzzle than those from the Atlantic. The females in Peru can weigh up to 58 kilograms (kg), while in Uruguay they weigh around 41 kg.

Differences are also manifested between males and females of one and the same region – and it seems to be more intense amongst the fur seals of Uruguay than those of Peru. The Uruguayan fur seals  show differences both in the shape and in the size of the skull, whereas, in Peru, differences are only noted in the size of the skull. “These differences can be attributed to variations in the reproductive system adopted in each population”, she says.
In the Atlantic, a male can literally keep a harem with up to 14 females during the whole reproductive season – there are three months of it, in the summer. Whereas in the Pacific, particularly in Peru, the fur seals  are luckier: each male chooses a rock on the beach and displays himself to the female. As they need to pass through his territory at the moment they go to the sea to refresh themselves and to look for food, the male charges a sort of toll. The female chooses the territory she is going to pass through, and consequently the male with which she is going to mate. “The harem system, which predominates in the Atlantic Ocean (Uruguay), calls for frequent and intense combats amongst the males, and it may have led to the more marked development of structures that are advantageous for combat”, says Larissa. “Whereas on the Pacific coast, combats are not very frequent, and the physical differences between male and female are less marked.”

The pinnipeds? the group to which the fur seals belong, and which includes seals, walruses and elephant seals – arose 22 million years ago on the west coast of the United States. About 3 million years ago, they went down past Central America and colonized South America. It is estimated that there exist today ten different species of fur seals, spread over America, Africa and Antarctica. Around here, there is no record of reproductive colonies of pinnipeds, and the fur seals coming from Uruguay only give the air of their grace during the autumn and the spring, to rest on Brazilian beaches.

One curiosity about these animals capable of reaching almost 2 meters and weighing 159 kg: for at least 300 hundred years, the species of fur seals  studied by Larissa has not inhabited the central region of Chile, an area of around 2,200 kilometers between Mejillones and Chiloé Island, possibly because of the absence of island, the preferred habitat at the time to reproduce and suckle the pups.

Uncertain sea
In the last 400 year, the cyclical warming up of the sea has made fish disappear from the Peruvian coast, in search of colder waters, during the El Niños. At normal times, the sea lion females remain up to three days at sea, after food; in years of the phenomenon, they spend as much as ten days, leaving on the beach their puppies, which end up dying of inanition, since the mothers take time to come back. Without food, the sea lion population diminishes considerably, but it returns to growth as the fish come back. In 1997, the fur seals came close to extinction: “The government thought that the solution for maintaining the fishing business was to cull the fur seals, because animals and fishermen vied for the available fish. Fortunately, they realized that it wasn’t necessary”, says the biologist, who that same year spent 45 days at the Peruvian environmental reserve Punta San Juan monitoring the swings in the temperature of the water and the number of matings and births, besides collecting samples from the fur of the pups for genetic analyses, under deafening protests from the females.

Would a new El Niño be capable of destroying all the fur seals in Peru? “It’s unforeseeable”, Larissa reckons. “As the fish and the fur seals started to reproduce again after the 1982 El Niño, one of the most intense in history and responsible for a high mortality of species, the tendency is for the fur seals to succeed in recovering, if there is no phenomenon so severe in a short space of time.”

The example of the otters
The fur seals, classified as predators at the top of the food chain in the marine ecosystem, eat fish, which devour marine invertebrates, which in turn feed on phytoplankton, responsible for the photosynthesis in the aquatic environment. The extinction of any member of this chain would occasion an imbalance in the environment in which the species lives.

A classic example was the decrease in the otters in Alaska, due to the oil spill from the Exxon Valdez ship in 1989. The mortality of thousands of otters in the region from contamination by heavy metals caused an uncurbed growth of sea urchins, their favorite food. These sea urchins ate the large forests of kelp, a kind of giant algae, and left the bottom of the sea looking like a desert. The algae carry out photosynthesis in the marine environment, and, with their absence, no kind of life maintains itself in the region. After a few years, with the recovery of the otter population, the equilibrium in the local ecosystem was reestablished.

Although the scenario may seem murky, there are alternatives for preserving the animals from the Pacific Ocean that appeared to be fated to extinction. In 1884, indiscriminate hunting almost brought about the extinction of the sea elephants from the north, leaving only 20 specimens on Guadalupe Island, in Baja California. The governments of the United States and Mexico adopted a rigorous policy of environmental conservation and prohibition of the hunting of these animals. Today, more than one century afterwards, the species has recovered and is estimated at about 175 thousand. From what everything indicates, this should be the way for the preservation of the fur seals that inhabit the seas of Peru and Chile.

The Project
Geographical variation in the Arctocephalus australis South American sea lion (nº 00/01340-0); Modality Regular Line of Research Project Grants and Doctoral Scholarship; Coordinator João Stenghel Morgante – IB/USP; Investment R$ 13,808.37 and R$ 105,144.00 (FAPESP) and US$ 1,000.00  (Society for Marine Mammalogy)

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