Impacts of male-only fishing and sperm limitation in manipulated populations of an unfished crab, Hapalogaster dentata

Abstract

We examined how changes in population structure resulting from fishing selectively for males, including a decrease in male size and a skewed sex ratio toward females, might influence the reproductive success of females in fished populations. We used Hapalogaster dentata as a model species for commercially important lithodid crabs. First, to verify the validity of using H. dentata as a model species, we examined the effects of male size and mating frequency on both male and female reproductive potentials of H. dentata. Male and female reproductive potential was very similar to some commercially important lithodid crabs. Male size and mating frequency affected the reproductive success of females, due to sperm limitation. Females had a limited period of sexual receptivity. These reproductive characteristics would be valid for using H. dentata as a model species. Second, to investigate the reproductive success of females in populations, we placed 16 artificial populations of H. dentata in artificial cobble plots similar to their natural habitat. The male size and sex ratio of these populations were manipulated. A sharp decrease in female reproductive success in response to their mating timing was observed in the populations comprising small males with a sex ratio skewed toward females. Additionally, the mean reproductive success of females in manipulated populations (i.e. SB population) decreased gradually as the reproductive season progressed. Our results indicate that a decrease in male size and a sex ratio skewed by male-only fishing would sharply decrease the reproductive success of females by sperm limitation. Commercially important lithodid crabs can be similarly impacted unless the legal size limit for males is adequate. © Inter-Research 2006.