358 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



they very soon found and attached themselves to the fish 

 that had been caught. The whelk proceeds by boring a 

 hole through the skin, inserting its snout, and then 

 devouring all the muscular tissue, leaving nothing but 

 skin and bones. The mollusc will not touch rotten fish, 

 but experiments have shown that it will devour anything 

 so long as it is fresh. Often enough, 10 to 20 whelks 

 would be found attached to a plaice, and the fishermen 

 estimated that one-third of the year's catch was lost in 

 the region investigated (Thisted Bredning, in Denmark). 



The experiments carried out by Petersen were of a 

 two-fold nature — (1) to determine the number of whelks 

 in a certain area, and (2) to find out whether these could 

 be economically exterminated by capture. The first 

 part of the work was carried out by using an instrument 

 called the "bottom-sampler," and also by the employ- 

 ment of a diver. The latter caught from 106 square 

 metres 100 whelks, 36 square metres 128 whelks, 106 

 square metres TO whelks, 106 square metres 97 whelks. 

 In the last two cases the man reckoned that he had 

 only taken one-third of the whelks present. From the 

 results it was calculated that 130 million whelks were 

 present in the region (an area of 65 million square 

 metres) . 



One motor boat, with 240 traps, was able to catch 

 3,845i bushels (45 tons of whelks !) in the same district, 

 between April 5th and November 8th. 



On the whole, it was concluded that the extermina- 

 tion by catching would not be an economic method, 

 especially since there did not seem to be any great use 

 for the whelks caught in the district. Petersen also 

 states that six or seven whelks' opercula may be found in 

 one cod's stomach, and comments on the rarity of any 

 remains of the shells. 



