By saying these figures are conservative （Line 1, paragraph 3), Dr. Worm means that ___

By saying these figures are conservative (Line 1, paragraph 3), Dr. Worm means that ________.

[A] fishing technology has improved rapidly

[B] then catch-sizes are actually smaller then recorded

[C] the marine biomass has suffered a greater loss

[D] the data collected so far are out of date

请帮忙给出正确答案和分析，谢谢！