Assessment Of The Effectiveness Of Skull Morphometric Indices For Discrimination Of Wild And Farmed American Minks

Many wildlife species which have important economic values are protected from further declining of population size. However, they are still under the pressure of poaching. Farming of wildlife can provide animal products sustainly and reduce poaching pressure. However, the poached products can enter markets in the name of farmed products, making domestication the "umbrella" of poaching. Therefore, it is necessary to develope reliable methods to discriminate wild products and farmed products to fight against poaching and protect wildlife farming. Skulls are the normal physical evidences in the poaching cases. However, methods to discriminate skulls are very limited and need to be developed.This study took the American mink (Neovison vison) as model animal, and proposed the hypothesis that the volume of braincase, respiratory passage indices and zygomatic morphology might be influenced by the differences of behavioral modes, movement intensity, utilization of bitting muscles between animals growing up in the wild and farm environment. To test the hypothesis, measurements were taken on skulls of wild and farmed minks including the median palatal length (MPL), mesopterygoid fossa width(MFW), nasal height (NSH), nasal width (NSW), braincase volume (BRV), zygomatic space (ZAS), zygomatic breadth at A (ZBA) and B (ZBB), condylobasal length (CBL), mandibular length (MDL), postorital constriction (POC) and greatest upper facial breadth (GFB). Fourteen indices were set up, namelyMPL/CBL, MFW/CBL, NSH/CBL, NSW/CBL, BRV1/3/CBL, POC/GFB,POC/CBL,POC/MDL,ZASSQRT/CBL,ZASSQT/MDL,ZBA*CBL/2ZAS,ZBA*MDL/2ZAS,ZBB*CBL/2ZAS and ZBB*MDL/2ZAS. Their effectiveness were tested for discriminating farmed (n=45) and wild animals (n=32). The results showed that respiratory passage, braincase volume and the zygomatic morphology were significantly different between wild group and farmed group (0.000<p<0.05). Among indices based on respiratory passage structure, MFW/CBL was effective with an overall correctness of discrimination 86.4% in two groups; the overall discriminative correctness of BRV1/3/CBL was 84.7%. POCICBL, POCIMDL, ZASSQRT/CBL, ZBA*CBL/2ZAS, and ZBB*MDL/2ZAS out of indices based on zygomatic arch morphology were effective with overall discriminative correctness ranging between 81.8% and 85.5%. Combination of multiple indexes might increase the effective correctness greatly. However, the skulls of farmed group fell into two types. Type Ⅰ had typical properties of farmed animals, while type Ⅱ was very similar to wild group. Therefore, type Ⅱ skull had apparent impact on the discrimination power of above indices. Besides, all indices showed significant sexual dimorphisms. The discrimination power of all indices would be improved in case that sexes were known. The findings of this study had general significance and potentially applicable to other small carnivores for the discrimination.