Droppings help Otter researchers

Verrіterische Nachlassenschaften provide new information about otter population

Using two new methods, UFZ researchers were able to obtain more accurate figures on the population of the otter in the Upper Lusatian heath and pond landscape biosphere reserve for the first time. © André Künzelmann / UFZ
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Researchers have developed two new methods to better assess the European otter population (Lutra lutra) and its impact on the pond economy. In this way they succeeded for the first time to obtain more accurate figures about the existence in the biosphere reserve Oberlausitzer heath and pond landscape.

The genetic analyzes of the feces used here can be a promising approach to investigate otter populations, write the scientists of the Helmholtz Center for Environmental Research in the journal Conservation Genetics. The new method can be used not only for otters but for all vertebrates. This information is needed to ensure effective conservation. Accurate information on the stock size of the otter makes it possible to calculate the amount of fish eaten per pond and thus the damage done to the pond economy in an area.

How common are otters?

Adequate compensation for damage improves the acceptance of the otter in the local pond industry and thus the protection of this endangered species, which is required by national and international laws. To determine the stock size, the classical method of catching, marking and restoring is extended by modern DNA analyzes.

How often the otter visits and hunts a lake can be estimated by taking into account the age of the feces traces. The second new approach makes it possible to significantly improve the accuracy of visitor rate tracking in many situations and is not limited to droppings, but can also be applied to other types of animal tracks (food marks, footprints and dwarf lanes), according to the international research team.

Gourmets with brown fur

At some point in the dusk, he strikes: Fish leftovers testify the next morning from the fish otter's meal. Since the nocturnal and dusk-active animals are particularly demanding of their environment, Lutra lutra is one of the most endangered mammal species in Central Europe. The gourmets with the brown fur and the many long felt hair on the mouth are extremely shy. Watching them is hard to catch them almost impossible. display

Detailed information on the size of the fish otter makes it possible to calculate the amount of fish eaten per pond and thus the damage done to the pond economy in an area. This is important for the appropriate compensation for damages and thus for the acceptance of this endangered species. Andr K nzelmann / UFZ

But how should the otter be effectively protected, if there are only very vague guesses about its existence? Experts estimate the stock of otters in the biosphere reserve Oberlausitzer Teichlandschaft at about 200 to 600 specimens. Fors of damage caused by otters in fishery businesses are compensated by the Free State of Saxony. Therefore, a favorable and simple method is needed, with which one can estimate the occurrence of otters, so that one knows, how much money one should pay as compensation, "describes Bernd Gruber of the UFZ one of the problems.

In practice, however, it is difficult to verify the actual damage. Otherwise someone would have to go every time to look at the fish and check for otter tracks - that's hard to do. "

The victim on the track

Like every bird, the otter leaves its mark. The researchers are now using these to better estimate the number of animals in an area than was previously possible. Up to thirty times a day, an otter makes a sign to show potential partners or competitors who is traveling in the area.

"The practical thing about the otter is that he uses his slogan - ie the feces - as a social means of communication and therefore puts him out exposed, which makes finding it extremely easy, " says Simone Lampa, who along with her UFZ Colleagues over the past two years has collected over 400 fecal samples in Upper Lusatia. As vertebrate cells on the surface of the intestine renew themselves and old ones are repelled, tiny traces of DNA are found on every piece of faeces, thereby betraying the sender.

Faternity test for otters

As with a paternity test, a swab is made using a cotton swab, which ends up in a plaster tube that goes to the lab. Compared to blood or tissue, however, DNA is only represented by very few cells. This makes the process difficult. "In addition, there is the problem that a high number of proteins, bacteria and enzymes in the feces end up in the detection process", reports Marion H hn, who is already testing the populations of Australian lizards by genetic testing Has. You need to get the DNA out and copy it several times to make it visible at all. This is fraught with big mistakes. The process must then be repeated several times to obtain the actual genotype.

Accordingly, researchers are glad that they could more than double the success rate compared to previous procedures. But her new method brings yet another decisive step forward: it combines modern genetics with the classic method of animal counting by catch and recovery. For this purpose, the animals have been caught, marked, released, caught again and eventually noted whether the animal was already marked or not.

"Genetic Fingerprint" is caught

After several fishing periods, it is possible to calculate by mathematical methods how many animals are there. Provided that enough copies go online. For the shy otters, this method is out of the question. Therefore, not the animal itself, but so to speak, its "genetic fingerprint captured" by the Kotspuren be evaluated.

For the accuracy of population estimation, it is important to collect the same points every day at equal intervals. The recovery rates should be as equal as possible, so as not to falsify the result by chance finds. The cost was about 30 euros per fecal sample.

"This is still cheaper than hiring a dozen people watching the area around the clock. It does not necessarily have to be feces, it is also hairy. You just have to get to the DNA. It will certainly be a matter of course in a few years time to estimate the size of the population, "Gruber suspects. But as everywhere else, the devil is in the detail here: attempts to determine the size of wild cat populations in this way failed a few years ago, because not enough cat hair stuck to the laid out adhesive strip.

Method suitable for each vertebrate species

Despite such setbacks, Lampa is also optimistic that genetic methods will reveal much more about animal populations in the future: "In principle, our method is applicable to every vertebrate species. You just have to design the genetic markers that mark the crucial DNA sections in the genome for each species. But many mammals already have it. "

How many otters now live exactly in Upper Lusatia, the researchers can not yet say. For this they still have to collect feces in many places. But at least for a small area there are now the first safe data: on the 305-acre study area between Hoyerswerda and Bautzen live 32 to 40 otters. There will be a residual amount of uncertainty in the future. Nevertheless, the new method has helped significantly to find out more about the elegant nocturnal swimmers in the fish ponds of Lusatia.

(idw - Helmholtz Center for Environmental Research, 06.06.2008 - DLO)