As part of the activities Protection and conservation of water and water-dependent ecosystems, which are held by Hrvatske vode, otter and beaver were monitored as the main indicator species of mammals for the project area. The subject monitoring was carried out by the company OIKON d.o.o. – Institute for Applied Ecology, in cooperation with the Public Institution Kopački rit Nature Park. One of the objectives of the research of these two strictly protected species was the capture and marking of captured otter and beaver individuals with GPS devices. One of the objectives of the research of these two strictly protected species was the capture and marking of captured otter and beaver individuals with GPS devices. Telemetry monitoring of these two species is an extremely demanding and complex process for several reasons. These are semiaquatic species that spend part of their lives on land and part in water. Their body structure is such that it is impossible to install a GPS device using a collar, as is the case with wolves, lynxes or bears. In addition, their body mass is smaller, so the GPS device itself must be smaller and lighter, which prevents a longer period of monitoring due to the capacity of the batteries in the GPS device itself, which is limited by mass and size. As part of the project, a total of 5 otters and 5 beavers were caught, and after tagging, they were released unharmed. A hand net was used for catching beavers, and cage traps with flaps on both sides were used for catching beavers, equipped with alarm devices and GSM cameras, so that at the moment of activation, trapping experts would be informed about the activation of the cage trap. The picture from the GSM camera would tell which animal it is. In accordance with the approvals/decisions of the Ministry of Economy and Sustainable Development and the Ministry of Agriculture, captured beavers are marked with GPS devices using the method of affixing them to the fur. The monitoring period was about 20 days. Caught otters are marked by attaching a leather strap to which a GPS device is attached. Each leather strap is equipped with a safety system (drop-off) which has the function that if the animal were to get stuck in the branches, then the animal could activate it with its own strength and the strap would come off the otter. Unfortunately for us, or luckily for one of the captured otters, this system was activated already 36 hours after capture, and the caught otter named Tonka dropped the strap and the strap was found in a thick blackberry with a torn drop off system.

All captured animals were sedated or put to sleep in order to minimize the stress of tagging and to keep the animal healthy and unharmed.

The collected telemetry data will be used to determine the size of the territories of individual species and to help estimate the size of the otter and beaver populations within Kopački rit.

In all phases of the project participated: Ph.D. Duško Ćirović, B.Sc. ing. biol., (Faculty of Biology in Belgrade) Dr. Vet. honey. Vedran Slijepčević (Veleučilište in Karlovac) and Marko Augustinović, mag. ing. silv., (OIKON d.o.o.) and employees of the professional protection, maintenance and preservation service of the Nature Park and the nature guard service of the Public Institution of the Kopački rit Nature Park.