Where’s the catch?

ABOUT 90% of the world’s fish stocks are being fished either to their limit or beyond it. Monitoring fish numbers reliably, though, is no easy matter. Official catch data are often incomplete and sometimes untrustworthy. Moreover, large tracts of the sea are not monitored at all. In order to know which species to conserve, and where, it would be handy to be able to establish fish numbers cheaply and reliably. Now, as they write in PLOS ONE, Philip Thomsen of the Natural History Museum of Denmark, in Copenhagen, and his colleagues think they have taken a step towards this goal.

Scientific surveys of deepwater fish are often carried out by trawling the ocean bed. This means towing a net over a set distance and then hauling it up to count the catch within. That, when due allowance is made for the size of the net’s mouth, yields a figure for the number of each fish species per square kilometre.

Every year a research vessel called Paamiut carries out surveys of this sort in the Davis Strait off south-west Greenland. This year it also had one of Dr Thomsen’s colleagues on board. At each of the 21 places Paamiut dropped her nets, he collected two litres of seawater from the bottom. The…Continue reading

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