That means a higher proportion of what is in the sea is being caught, so the real difference between present and past is likely to be worse than the one recorded by changes in catch sizes.
①Dr. Worm acknowledges that these figures are conservative.
②One reason for this is that fishing technology has improved.
③Today’s vessels can find their prey using satellites and sonar, which were not available 50 years ago.
④That means a higher proportion of what is in the sea is being caught, so the real difference between present and past is likely to be worse than the one recorded by changes in catch sizes.
⑤In the early days, too, longlines would have been more saturated with fish.
⑥Some individuals would therefore not have been caught, since no baited hooks would have been available to trap them, leading to an underestimate of fish stocks in the past.
⑦Furthermore, in the early days of longline fishing, a lot of fish were lost to sharks after they had been hooked.
⑧That is no longer a problem, because there are fewer sharks around now
③(并列：分1)今天的船只可以使用 50 年前还没有的卫星和声波定位仪来寻找猎物。