Wetenschap - 23 maart 2012

New blood will help otter population

The otter is doing well in the Netherlands. But danger lurks in the form of inbreeding.


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Otter expert Dennis Lammertsma of Alterra says this in response to an alarm call to state secretary Henk Bleker made in a letter from the Das&Boom and the Dutch Otterstation foundations. According to these foundations, the otter is in danger of dying out again if the right steps are not taken. Lammertsma wants to put this alarming message into perspective.
According to Lammertsma, the otter population in the Netherlands and their natural habitat are still growing. However, a possible threat is looming up: the consequences of inbreeding. 'Inbreeding is a process which lessens genetic variation. That isn't really a problem in itself. The danger is in a so-called inbreeding depression. This means that the negative effects of inbreeding will lead to mortality and less procreation. But I don't see any indications that this is a serious problem at this stage.'
New blood
Inbreeding itself can be easily 'countered' by bringing in new blood. The easiest way is to introduce new and genetically unrelated animals. Das&Boom calls on Bleker to take immediate steps in the process of rehabilitation. It points to the (international) obligation that the Netherlands has to protect the otter and its habitat. Das&Boom also calls for scientific monitoring of the otters to be resumed. 
Analysis of droppings
Alterra had been monitoring the development of the otter population till the winter of 2010. That was done by collecting and genetically analyzing otter droppings. Then the ministry of EL&I stopped its financial support. Currently, inbreeding has made it impossible to do an adequate parental analysis, says Lammertsma. The animals have become genetically much too similar to one another. 'The resolution needed to differentiate parent-child relationships has become too small. But we can still see how many animals there are and the extent of the inbreeding.'
Lammertsma would very much like to see the monitoring resumed. In fact, this is a prerequisite before new animals can be released, he says. 'You can't release animals into an area already populated by other otters. They won't stand a chance at all. So you need to monitor an area before you release otters.'