TAMONE, S/L; ANDREWS, A; MONDRAGON, J; NIELSEN, J; TAGGART, S/J; University of Alaska Southeast; USGS Alaska Science Center; USGS Alaska Science Center; USGS Alaska Science Center; USGS Alaska Science Center: Circulating Ecdysteroids In Tanner Crab, Chionoecetes bairdi are Indicators of Molting Probability.
Tanner crab, Chionoecetes bairdi , is a commercially important crab fished in southeastern Alaska. The legal size for this crab in this fishery is 130 mm. These crabs increase by shedding their hard exoskeleton in a process termed molting. Female Tanner crabs are known to undergo a terminal molt, which coincides with sexual maturity. Males on the other hand molt more times than females and can thus attain larger carapace widths than females. Males undergo a morphometric change in chelae size that is not linked to reproductive maturity. This change, however, has been hypothesized to occur during the male�s terminal molt. Male Tanner crab with morphometrically large chelae occur over a broad size range (55-200 mm). Ecdysteroid hormones regulate molting and circulating ecdysteroid concentrations can serve as an indicator for molting probability of crabs. We collected Tanner crabs from Glacier Bay and recorded the carapace width, chelae height and shell condition. Males sampled in this study ranged in carapace width from 37 to 174 mm. Blood samples (1.0 ml) were collected and assayed for ecdysteroids using an enzyme-linked immunoassay (ELISA). Crabs with low ecdysteroid levels and large chelae size (CH:CW ratio < 0.19) were assumed to have undergone a terminal molt, which allowed us to estimate the proportion of the population that was terminally molted. Circulating ecdysteroids were significantly higher in crabs with small chelae than terminally molted crabs (177.9 � 15.4 ng/ml; 11.1 � 3.4 ng/ml). Considering crabs with small chelae circulating ecdysteroids correlated well with shell condition. Crabs most likely to molt (old shelled) had the highest levels of hormones. Crabs with very old shells (terminally molted and those with small chelae) had significantly lower levels of ecdysteroids, indicating that these crabs maintained a low probability for molting.
