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ŠUMARSKI LIST 11-12/2021 str. 25     <-- 25 -->        PDF

To determine the number of lynxes in Central European populations, it is recommended to use a 2.7 x 2.7 km cell grid (Zimmermann et al. 2013), while in the Slovenian part of the Dinaric population, a 3 x 3 km grid was used (Fležar et al. 2019). In this study, it was not possible to cover the entire study area with recommended density of camera traps, due to the financial limitations. Moreover, areas of Kapela and Velebit mountains were partly not accessible due to the danger of mine fields. Therefore, our results present the minimum and not the actual number of lynx individuals present in Croatia in the studied period. Until now, results of population census using camera traps were published for several Eurasian lynx populations. The largest dataset comes from Switzerland, where monitoring with camera traps started already in 1999 (Pesenti and Zimmermann 2013). Weingarth et al. (2012) used camera traps for the estimation of lynx population size in German National park Bavarian forest, Blanc et al. (2013) we considered 4 scenarios comparing low versus high detection probability and small versus large populations and contrasted abundance estimates obtained from both approaches. Standard CR and SECR models both provided minimally biased abundance estimates, but precision was improved when using SECR models. The associated confidence intervals also provided better coverage than their non-spatial counterpart. We concluded SECR models exhibit better statistical performance than standard closed CR models and allow for sound management strategies based on density maps of activity centers. To illustrate the comparison, we considered the Eurasian lynx (Lynx lynx) implemented their research on French Jura Mountains, while Gimenez et al. (2019) estimated lynx population size in French part of Jura and Voges in the period from 2011 until 2016. In these studies, camera traps were active between two and four months per year, mostly during the winter months (January – April), but area of survey were much smaller than the area covered in this study. One of the challenges of population monitoring on such a large area arises from the different terrain configuration and the differences in previously available data for certain areas. For instance, we noticed differences in the quality of results between the two geographical areas - Gorski kotar (i.e. Primorsko - Goranska county) and Lika (i.e. Ličko-Senjska county). In Gorski kotar, a significant number of marking sites were known from previous research period (Kusak 2012; Kusak and Modrić 2012; Kusak et al. 2013; Kusak et al. 2014), while in Lika (except northern Velebit and Plitvice Lakes National Park) photo-traps have never been used before to monitor lynx. As a result, in Gorski kotar (where most of camera traps are placed on marking sites) we have a higher percentage of animals identified based on both flanks, and a lower proportion of animals of unknown sex and those recorded only once. To reach this level of data reliability in Lika, it is necessary to enhance our camera trap network, what was not been possible in all locations within this study.
During the two seasons, we identified a total of 89 - 108 adult lynxes. During the second season (2019-2020) we determined that a minimum of 69 - 82 adult lynxes were present in Croatia. The fact that we conducted monitoring throughout the year and had a high percentage of animals recorded only once (27.8%), indicate that we recorded a certain number of individuals in dispersion. Probably those individuals did not establish a territory in Croatia but were recorded in their search for territory or during the mating season. Another explanation for the low rate of repeated records could be insufficient detectability of lynxes caused by low density of camera traps in some areas, then also partly by eventually high turnover of lynx individuals in Dinaric population. Although 43.5% of individuals identified in 2018 - 2019 were not photographed during the 2019 - 2020 season, we cannot claim that all of those individuals perished from the population but probably some of them were not captured due to the low density of camera traps. Also, results of long-term monitoring in certain areas (Gorski kotar, northern Velebit) suggest that some animals are re-recorded (recaptured) after more than a year of absence from photo-traps (unpublished data).
The actual lynx number is more likely to be closer to older estimation of 130 lynxes (Firšt et. al. 2005), then to later estimation of 40 – 60 individuals (Sindičić et al. 2010). This wide variation in estimates illustrates the importance of properly designed and performed monitoring system. This research presents the first published scientifically – based estimation of lynx population size in Croatia. Thus, we cannot state that there was an increase in lynx population size in Croatia when we compare this study with past results. Future important steps in lynx population monitoring are correcting the deficiencies identified in this study and implementation of methodology that will allow us to use spatial capture recapture models.
We would like to express our gratitude to numerous collaborators who participated in the data collection: Tomislav Rukavina and Josip Frketić Public institution “Nature Park Velebit”; Franjo Špalj and rangers of the Public Institution “National Park Paklenica”; Public Institution “National Park Northern Velebit”; Public Institution “National Park Risnjak”; Public Institution “National Park “Plitvička Jezera” with park rangers Ivica Matovina and Dalibor Vuković, Public Institution for Nature Protection of Primorsko-Goranska county “Priroda”; Ivan Grubišić and Matija Marek from Geonatura Ltd., Zvonimir Kranjčević, Ivica Medarić, Edi Cirka, Dina Botta, Paul Jedriško, Amir