Testing carapace morphology characteristics for field identification of Chionoecetes hybrids

Testing carapace morphology characteristics for field identification of Chionoecetes hybrids

D. Urban, D. Pengilly, L. Jadamec, and S.C. Byersdorfer

Testing carapace morphology characteristics for field identification of Chionoecetes hybridsThis is part of Crabs in Cold Water Regions: Biology, Management, and Economics
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Description

The ability of Tanner crabs, Chionoecetes bairdi, and snow crabs, C. opilio,to hybridize in the Bering Sea was first recorded in 1969 and biologists since then have struggled with the identification of the various forms of the hybrids. The hybrids are not uniformly intermediate between the parental types, but form a smooth cline of morphological types making the field identification of hybrids a difficult and subjective task. Over 1,000 genetically typed carapaces were examined in an effort to develop an accurate field identification technique for hybrids and their parental species. An ordinal scoring system was developed for six morphological characters with scores ranging from 1 for C. bairdi to 5 for C. opilio, with hybrids being intermediate. Photographs of character variation by crab type are presented. A classification tree and discriminant function analysis were applied to learning sets of carapace scores, and then to test sets, but neither technique could reliably identify carapaces when applied to data outside of the individual learning and test sets. The scoring system developed here can be used with good success for developing a classification scheme for a single scorer, but inconsistency of scorers, as demonstrated by components of variance analysis, proved an impediment to developing a broadly applicable scheme.

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