Potential mechanism underlying the decline in kuruma prawn Penaeus japonicus: effects of loss of large females on reproductive traits and recruitment success

Le résumé fourni par la source

Despite the disproportionate contribution of large females to reproduction via, for example, the female size-fecundity relationship and maternal influences, larger individuals are more likely to be caught than smaller ones. Removal of larger females that tend to spawn earlier in the spawning season is expected to shorten the spawning season and delay its commencement, which may have a significant effect on recruitment to the population. To elucidate the mechanisms underlying the recent decline in Penaeus japonicus resources, we investigated the temporal trend in female body size and the effects of loss of large females on reproductive traits and recruitment success using fish market surveys, a field survey, a field experiment, and a mark-recapture experiment in the Seto Inland Sea, Japan. Female body size has decreased significantly over the last 20-30 yr. The loss of large females (>220 mm body length) was associated with a shortened spawning season and delayed timing of spawning season commencement. The delay in postlarval settlement likely resulted in a decrease in recruitment success through seasonal changes in predation pressure on juveniles. In addition, loss of large females is expected to decrease and cause fluctuations in the reproductive and recruitment success through the size-fecundity relationship and maternal influences. Our findings suggest that loss of large females has unexpectedly serious effects on reproduction and recruitment by altering female reproductive traits. Preservation of female reproductive traits while maintaining the population size structure should be recognized as an important goal for the sustainable resource management of P. japonicus.

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