THOMTON, J. D.*; TAMONE, S. L.; Univ. of Alaska, Fairbanks; Univ. of Alaska, Fairbanks: Measuring ecdysteroid levels to assess physiological state in Alaskan Dungeness crab populations

Research on Dungeness crab (Cancer magister) has revealed a significant difference in the reproductive and growth cycles between populations of crabs in Alaska versus Washington, Oregon and California. Understanding the reproductive biology of C. magister in Alaska is important for managing the fishery and may lend clues to the thermal tolerance of this species. This research aims to elucidate the temporal physiological changes associated with reproduction and growth in Alaskan C. magister through the quantification of molting hormones (ecdysteroids) in hemolymph. The reproductive cycle (molting, mating, egg extrusion, and brooding) occurs annually in southern populations, however Alaskan C. magister exhibit both annual and biennial cycles. Mating in this species occurs soon after the female molts (June-July) and is in the soft shell condition. During that same year, an unknown percentage of females undergo oogenesis and fertilization of eggs during autumnal extrusion. The following year some females molt and may extrude while others skip-molt and may extrude by utilizing stored sperm. By measuring levels of ecdysteroids, molting probabilities can be determined. Hemolymph samples were collected from wild female crabs and analyzed for ecdysteroids using an enzyme-linked immunosorbent assay (ELISA). Preliminary results reveal that 94% of the sampled females had low levels of circulating ecdysteroids (<50 ng/ml) and large mature ovaries. The remaining 6% had high levels of ecdysteroids (>300 ng/ml) with no ovarian development and were in late-stage premolt. The females with low levels of ecdysteroids had worn carapaces indicating a skip-molt cycle, which along with mature ovaries supports a biennial growth cycle for 94% of the female crabs sampled.