366 K. Çiçek et al.
TABLE 1 Parameters of the matrix model for the harvested population of Anatolian water frogs (Pelophylax spp.) in southern Turkey. Survival rates
Reproduction
Year 2013
2014 2015
Mean3
Mean, corrected for emigration4 Standard deviation
Juvenile (Sj) Adult (Sa) Number of adult females1 0.430
0.331 0.288 0.350 0.400 0.073
0.576 0.612 0.498 0.562 0.612 0.058
1,758 1,680 1,389
Number of juveniles1 1,588
1,872 770
F × Sa
0.532 0.229 0.381
0.214
1Calculated with CAPTURE (maximum of the estimates for the three seasons). 2Calculated by dividing number of juveniles in a year by the number of adults in the previous year (see text for details). 3Survival rates are before correcting for emigration (i.e. apparent survival rates). 4Upper bound of mean survival rate, corrected by assuming 5% emigration (see text for details).
are based on the apparent survival rates (f) calculated using the Cormack–Jolly–Seber model, but modified as follows. As this model cannot distinguish between emigration and mortality, apparent survival rates underestimate true sur- vival to a degree dependent on emigration. We did not have data on emigration (or data that would allow a spatial Cormack–Jolly–Seber model). Based on the high site fidelity and the typical home range size of amphibians (Smith & Green, 2005) compared to the size of our sampling areas, we assumed the emigration rate to be 0–5%, and estimated survival rates Sj and Sa as the sum of the corresponding apparent survival rate and emigration rate. We used annual total population sizes (N) calculated using CAPTURE as the initial population size in the population viability ana- lysis. For all model parameters we pooled the data from the five of the 10 locations that had harvest pressure. We in- corporated natural temporal variability (using the estimated standard deviations between years), demographic stochas- ticity and ceiling-type density-dependence (Akçakaya, 1991, 2013). Carrying capacity was set at half the observed popu- lation size (because we modelled only females). We simu- lated the dynamics of a harvested population for 50 years and 1,000 replicates (iterations) using RAMAS Metapop (Akçakaya, 2013).
Modelling harvest impacts
To explore the effects of harvest on population dynamics,we constructed amodel of a non-harvested population. Because we did not have sufficient data from non-harvested areas,we assumed that our catch effort and efficiency were compar- able to harvest effort and efficiency, and inferred survival rate in a non-harvested population (S′) based on our catch rates. This is a reasonable assumption because we used the same effort and methods for catching as those used by har- vesters. However, harvesters may be more efficient than we were and thus we consider our catch efficiency to be amin- imum bound of the efficiency of actual harvest. To calculate survival rate in a non-harvested population (S′), we assumed
that naturalmortality (1−S) andmortality as a result of har- vest (H) are independent. In this case, survival rate (S)in a
harvested population is S = S′(1−H). Thus, survival rate in a non-harvested population is S′ = S/(1−H). Here, H is the proportion of individuals of a pre-harvest population that
arekilled by harvest. Since thedata wehaveis the ratio, T, of the number of harvested individuals to the post-harvest population size (i.e. population already reduced by harvest), we calculated harvest mortality as H= T/(1 + T). To explore the impact of different harvest levels, we developed models with estimated survival rates for a non-harvested popula- tion, and ran simulations with harvest mortality varying from 0 to the value we estimated for the study populations. Because the type of density dependence may influence the impact of harvest, we used two types: a ceiling model, and a contest-type model (Akçakaya et al., 2007; see Results for details).
Harvesting history and export statistics
Frog trade data were obtained from the Turkish Statistical Institute (TÜİK). We also checked newspapers for trade news, most of which show illegal harvesting. This helped us supplement the statistical reports with information on illegal and off-the-record harvesting. In addition, during fieldwork we talked to exporting companies, local people and harvesters about their businesses and livelihoods (Sup- plementary Material 1).
Results
Demography, population viability analysis and harvest modelling
During the 3 years of fieldwork we captured and marked atotal of 13,811 Anatolian water frogs, of which 10,295 were adults. The mean weight of all sampled frogs was 19.46 g; only 19% of the captured individuals were .30 g, which is the minimum weight at which frogs may be harvested
Oryx, 2021, 55(3), 364–372 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605319000176 2
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