. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. SEA OTTER SEX DETERMINATION FROM SKULLS 181 selected on each graph such that most male measurements were plotted above it and most females below. The selected point, or "Key Value", was picked to produce the fewest incorrect or uncertain measurements. Since sea otters in the northern parts of their range are larger than those from southern locations (Roest 1973,1979), separate bar graphs were constructed for skulls from diff
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. SEA OTTER SEX DETERMINATION FROM SKULLS 181 selected on each graph such that most male measurements were plotted above it and most females below. The selected point, or "Key Value", was picked to produce the fewest incorrect or uncertain measurements. Since sea otters in the northern parts of their range are larger than those from southern locations (Roest 1973,1979), separate bar graphs were constructed for skulls from different parts of the range. These geographic groupings represented specimens from California (119), British Columbia-Washington-Oregon (9), Prince William Sound (22), the Alaska Peninsula (36), Adak Island (39), and Amchitka Island (101). Data are not available for sea otters from the Russian parts of the species' range. A bar graph developed for condylobasal lengths for sea otters from California illustrates the method (Figure 2).. FIGURE 1. Skull measurements used to determine the sex of a sea otter skull. Cd = canine tooth diameter; C8L = condylobasal length; MW — mastoid width; SkL = total skull length; ZW = zygomatic width; bo and bs indicate the basioccipital and basisphenoid bones, between which lies the BO/BS suture. This suture is not visible in adult skulls. In attempting to work out a relatively simple system for sexing otters, various combinations of these five measurements were tried, to see if a single value or formula could be developed. The most effective combination proved to be a simple summation of all the measurements, with one adjustment. Since the first four measurements all have values near 100 mm, while the canine tooth diame- ter is usually near 10 mm, the relative value of the canine in a summing combina- tion is only one-tenth that of the others. To equalize the relative values of the measurements, the first four were converted to one-tenth their act
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