Fisheries biologists can record tlie deptlis 

 and distribution of fisii wittt tlie "sharl< 

 recorder", an eclio sounder towed beliind a 

 boat. It produces an echogram (left) which 

 shows a shoal of fish near the bottom. Some 

 fish in deep water, at the left of the 

 echogram, are moving toward the surface. 



A small (legally undersize) plaice escapes 

 from the net and has an opportunity to breed. 

 Fish conservation depends largely on regu- 

 lating the mesh size of nets, which can be 

 measured by a gauge (right) . 



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