Morphometry and Maturity of Paired Tanner Crabs, Chionoecetes bairdi, from Shallow- and Deepwater Environments

Abstract

Paired male and female Tanner crabs, Chionoecetes bairdi, in a premating embrace were collected from shallow-(< 13 m) and deepwater (> 150 m) benthic environments by scuba and submersible, respectively. Pubescent females were restricted to shallow water; males grasping them were significantly smaller than those grasping oldshell multiparous females with eyed embryos in a large, deepwater mating aggregation. Males appeared to select for large sizes among pubescent females, but not among multiparous females, which were limited in size range. Grasping males were 82.6–166.2 mm carapace width (CW) [Formula: see text] and represented at least three different width frequency modes; all were larger than their female partners. Paired females represented two modes with mean CW ≈ 77 mm for pubescent and 99 mm for multiparous individuals. Only one to three of 176 male graspers were small-clawed (morphometrically immature), a statistically nonsignificant proportion; several others had partially regenerated claws but were otherwise morphometrically mature, as evidenced by the second right merus. These data support the hypothesis that the attainment of morphometric maturity, evidenced by a relatively large chela to body size ratio, is a prerequisite for functional maturity, the ability to mate competitively in wild populations.