Relationship of molting, gonadosomatic index, and methyl farnesoate in male snow crab (Chionoecetes opilio) from the eastern Bering Sea

Abstract

Snow crabs, Chionoecetes opilio (Fabricius, 1788), have a complex mating system, and understanding their reproductive physiology is paramount to crab fishery management. Mating and molting are inextricably linked, so the energetically demanding molting process may compromise male mating potential for some period prior to and after the molt. Recently molted, new-shell males are targeted preferentially during the commercially valuable eastern Bering Sea (EBS) fishery. Old-shell males, or males that have not molted within the last year, are not as visually appealing, but may have greater reproductive capacity and can contribute disproportionately to the genetic stock. We measured a crustacean reproductive hormone, methyl farnesoate (MF), and reproductive fitness, using gonadosomatic index (GSI) as a proxy, in EBS male snow crab to determine differences in reproductive potential between adolescents and adults. We compared these reproductive indices in new- and old-shell males as a broad estimate of the effect of molting biology on reproduction. Circulating MF was significantly higher in new-shell adolescent males compared to old-shell adolescent males and old-shell adult males, suggesting a juvenilizing rather than gonadotropic role for MF in C. opilio. New-shell males had a significantly lower GSI compared to old-shell males for both adolescent and adult males. The lower GSI measured in new-shell adults compared to the significantly higher GSI levels measured in old-shell adults suggests that new-shell males harvested during the commercial fishery lack the reproductive capacity of the old-shelled adults and therefore may not be contributing equally to the population.