AND ITS EFFECT ON THE CRAB AND LOBSTER FISHERIES. 271 



only point to the well-ascertained facts concerning the plagues and 

 migrations of lemmings* and locustsf in support of this statement.;|: 



The information we possess concerning the present plague of octopus 

 points to a precisely similar conclusion — viz. an abnormal multiplication 

 of these creatures on the French shores of the Channel and in the 

 Channel Islands, dating back with some degree of probability to the 

 year 1893, and followed in 1899, when the plague on the French coast 

 had reached its height, by migrations outwards from the overcrowded 

 centres of multiplication. 



I have no detailed information as to the devastation effected by these 

 creatures on the French coast (beyond the statement that they have 

 done enormous damage to the shell fisheries in general), but the changes 

 they have already wrought in our own waters are sufficient to show 

 their probable character. In Plymouth Sound they have not only 

 attacked the edible crabs {Cancer pagurus) and lobsters (Homarus 

 vulgaris), but have temporarily exterminated the larger swimming crabs 

 (Portimus p2iher and dcpurator) which in previous years have always 

 been found in great abundance in the harbour. During the last few 

 months it has been impossible to obtain more than isolated specimens 

 in the shrimp trawl, although in previous years scores, and even 

 hundreds, at a time could be obtained. In the Laboratory aquarium the 

 octopus attacked and devoured all the specimens of the commoner 

 British octopod, Eledone cirrlwsa, which were living in the same tank. 



III. Eemedial Measures. 

 There is no reason to believe that the present plague of octopus will 

 continue for more than one or two seasons, since the creature would 

 long ago have established itself on our shores if the conditions had 

 been suitable for its permanent residence. The species is a warm-water 

 animal, and belongs, like many other occasional visitants of our south- 

 western shores, to an assemblage of types which are distributed from 

 the Mediterranean to the southern shore of the English Channel. The 

 extension of these types to the north and east is usually limited by a 

 line drawn from Start Point to the Cherbourg peninsula. As types of 

 this fauna may be mentioned the ormer or ear-shell {Haliotis tuhcrculata), 

 the crayfish {Palimirus vulgaris), the cotton-spinner {Holothuria nigra), 

 and the pilchard or sardine {Clwpea pilchardus). The barrier to the 

 north-east, constituted roughly by the Start-to-Cherbourg line, is largely 

 one of temperature. Eastward of that line the mean yearly temperature 



* CoLLETT, Myodes leramus, its Habits and Migrations in Norway. Cliiistiania 

 Videnskabs-Selskabs Forhandlinger, 1885, No. 3. 



t MuNRO, The Locust Plague and its Suppression, London, 1900. 



i Cf. Latter, The Recent Plague of Wasps, Natural Science, iii., Oct., 1893, p. 273; 

 also cf. vi., 1895, p. 178. 



