368 K. Çiçek et al.
TABLE 2 Estimation of harvest mortality and the parameters of the matrix model for a non-harvested population. Year
Capture or harvest T2
2013 2014 2015
Mean5
Mean, corrected for emigration6 Standard deviation
0.420 0.415 0.434
H3
0.296 0.293 0.303
Survival rates1 Juvenile (S′j)
0.611 0.468 0.413 0.497 0.547 0.102
Adult (S′a) 0.818
0.866 0.714 0.800 0.850 0.078
1S′ = S/(1−H), an estimate of the apparent survival rate in a non-harvested population, where S values are from Table 1.
2Number of captured individuals, divided by the total population size as estimated with CAPTURE. 3H= T/(1 + T), an estimate of the proportion of individuals of a pre-harvest population that are killed by harvest (i.e. harvest mortality).
4F × Sa×(S′a/Sa) where F × Sa is from Table 1 (thus, assuming the same F as in a harvested population). 5Mean apparent survival rate and mean fecundity in a non-harvested population. 6Upper bound of average survival rate in a non-harvested population, corrected by assuming 5% emigration (see text for details).
Harvesters must have a licence from the provincial Food,
Agriculture and Livestock authority (Kürüm, 2015). Most harvesters have a low income, no permanent job and no social benefits (authors, pers. obs., 2014;Akın & Bilgin, 2010). For some, frog harvesting is their main source of in- come; it does not require capital investment. Other harvest- ers are seasonal farm workers who hunt frogs for additional income. Harvesters hunt at night, in groups of 3–4. Only one
in a group has a hunting licence, which is legally sufficient. Price per kg depends on demand, but is usually TRY 3–12 (USD 0.6–2.6). Companies offer the harvesters the highest price (12 TRY/kg) in the winter. One person can typically harvest 20–39 kg of frogs per night, but sometimes the har- vest can be up to 60 kg. Harvesters use flashlights or pressur- ized paraffin lamps as a light source (Supplementary Plate 1). One person holds the light and others collect the frogs by hand or net and place them in cloth bags. As the export companies do not buy dead frogs, harvesters keep bags of 3–4 kg (Supplementary Plate 2) in a cool place until the end of a night’s harvest, and they are then despatched for processing and packing (Supplementary Plate 3).
Discussion
FIG. 2 The effect of harvest rate on (a) total harvest over 50 years (thousands of individuals), and (b) probability that the population will fall below 1,000 individual frogs any time in the next 50 years, based on stochastic simulations. The gray shading indicates uncertainty that results from the type of density dependence model used (ceiling or contest).
Our study shows that Anatolian water frogs are harvested at high and unsustainable levels in southern Turkey. Simulations of the harvested population dynamics indicate a 90%risk of extinction within 50 years, with a probable year of extinction in c. 2032. Simulations show that if harvest mortality was to be reduced from the current estimated value of c. 0.3 (H in Table 2)toc. 0.05, not only would the risk of a population crash decline sharply but the total expected harvest over the next 50 years would be much higher (Fig. 2). This suggests that current harvest levels are probably unsustainable and could lead to extirpations of the harvested populations. Because we do not have data on the proportion of popula- tions that are harvested at these levels, we cannot make projections about the status of the species in this region. However, if harvested populations become extirpated, har- vest pressure could shift to, and threaten, other populations that are currently stable. Our results also show that enfor- cing strict harvest regulations would not only protect these frog populations but also help the local economy by pro- viding a source of income that is sustainable in the long term.
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
Reproduction 4
F × S′a
0.753 0.329 0.541
0.300
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