他们的方法并不是要评估特定海域鱼种的实际生物量，而是评估在这一段时间内生物量的变化。
知识点解析
这是一个简单句，但是宾语是两个，一是the actual biomass(the amount of living biological matter) of fish species in particular parts of the ocean，一是changes in that biomass over time。
rather意为“宁愿；有点，相当”。I’d rather stay at home.（我宁愿呆在家里。）He is rather lazy.（他有些懒。）有时rather在句中表示转折，或者对前文进行纠正（经常与or连用)。There are five, rather six, persons killed in the traffic accident.（在这场车祸中，共有5人，应该是6人死亡。）
According to their latest paper published in Nature, the biomass of largepredators (animals that kill and eat other animals)in a new fishery is reduced onaverage by 80% within 15 years of the start of exploitation. In some long fished areas, it has halved again since then.
