374 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



crabs land on city streets and finally even penetrate into houses. 

 This happened in 1931 in Rathenow on the Havel, in 1936 in a suburb 

 of Magdeburg, and in 1938 in Calbe on Saole. The habit of the mitten 

 crabs to leave the river bed led to the main methods used in Germany 

 to control them. Where the mitten crabs leave the river in their 

 efforts to get by the obstructing dam by land, extensive shore regions 

 below the dam are shut off by means of sheet iron and trenches dug 

 in the ground in front of the metal into which the mitten crabs fall 

 while wandering along on the sheet iron. Such a project has been 

 laid out by the Elde rivulet in Doemitz and has already been de- 

 scribed, and also in Garz on the Havel, where 77,100 kg of mitten 

 crabs were caught in 1935 and 58,300 kg in 1936. In Gruetz on the 

 Havel, 12 km above Garz, a conduit has been led along the upper 

 border of the slanting walled riverbank, and into this conduit the 

 climbing mitten crabs fall and are led by it to a large pit in which they 

 collect without being able to escape. A slanting piece of sheet iron 

 between the conduit and the river prevents the crabs from circum- 

 venting the traps. Although here only those crabs are caught which 

 escape the traps in Garz through parallel river beds, nevertheless 

 11,250 kg of crabs were caught in 1935 and 32,400 kg in 1936 (pi. 4, 

 fig. l;pl. 7). 



In Calbe on the Saole, the mitten crabs preferably climb up the 

 rough slanting wall below the dam which affords these adept climbers 

 sufficient grip. Here large wire baskets have been suspended against 

 the wall and at some distance above them sheet iron has been laid. 

 The climbing crabs slide down this sheet iron and fall into the basket 

 from which they cannot escape. In 1936, 47,440 kg were caught in 

 these baskets during the catching period from April to August (pi. 8). 



No special traps need be laid to catch the old downstream-migrating 

 animals. They always move with the strongest current and are 

 therefore caught in front of the turbines and in the eel-basket pots 

 behind the dam outlets. In this way 49,400 kg (about 227,000 

 specimens) were caught in 1935 in the Havel and 4,814 kg (about 

 34,470 specimens) in 1935, and 4,836 kg (about 27,560 specimens) 

 in 1936 in Bremen. 



These numbers do not by any means include all the mitten crabs 

 caught. The young crabs migrating upstream, which pile up in 

 front of the dam, are often caught there in large numbers in the eel- 

 basket pots kept in front of the dam through the summer. Including 

 these catches, the total catch of crabs moving up and downstream 

 was 137,650 kg in the Havel in 1935 and 129,300 kg in 1936. In 

 verified catches in Germany, altogether 262,600 kg were caught in 

 1936 and 190,400 kg in 1937. 



