Population structure of daytime surface swarms of Nyctiphanes simplex (Crustacea: Euphausiacea) in the Gulf of California, Mexico

During February, March and April, 57% of the euphausiids were in breeeding condition; males possessed developed spermatophores while females were carrying eggs and metanauplii. Sex ratios of female:male were between 1:1 and 2:1. Swarm samples contained high numbers of eggs and metanauplii. Swarming is related to reproductive activity, but analysis of one swarm sample of N. simplex showed that only 8% were in breeding condition. Highest biomass found was 32.6 g wet wt m^-3, correlated with the high trophic activity observed in the sample area. -from Author