262 THE PLAGUE OF OCTOPUS ON THE SOUTH COAST, 



In the Fourteenth Annual Keport (for 1899) of the Inspectors of Sea 

 fisheries (England and Wales), an exceptional abundance of octopus 

 is recorded by the collectors of fishery statistics for Babbacombe, 

 Torquay, Brixham, Yealm, Mevagissey, Cadgwith, and Mousehole, all 

 of which are fishing ports on the south-east coast of Devon and 

 Cornwall. The collector of statistics at Plymouth reports a lack of 

 evidence as to any exceptional prevalence of octopoda off this port, 

 but the information obtained by ourselves leaves no doubt upon the 

 matter, 



I have attempted below to throw light upon the three practical 

 aspects of this plague of octopus : (1) its cause, (2) its effects on 

 the shell fisheries, and (3) the possibility of arresting its continuance 

 by remedial measures. 



I. Cause of the Plague. 



There can be no doubt from its widespread character that the plague 

 is due in the first place to an exceptional multiplication of octopus in 

 recent years. There is some evidence, as will be shown below, that the 

 octopus move about in marauding bands ; but this is probably a local 

 phenomenon, that cannot account for the exceptional abundance of 

 these creatures on both shores of the Channel. 



The suggestion made in the paragraph from the Western Morning 

 News, above cited, is, in my opinion, nearer the truth, viz. that the 

 cause of their prevalence is connected with the heat of recent summers. 



We unfortunately know nothing directly concerning the rate of 

 growth of this large octopod. Many small mollusks attain their full 

 size and maturity in their second year, as I have myself shown,* but 

 there is abundant evidence that the larger mollusks require a number of 

 years to attain the same condition. This is well seen in those shell- 

 bearing mollusks which form fringes f (varices) on their whorls. The 

 rate of growth in littoral, as well as most land animals, is not even, but 

 is subject to alternating periods of active growth and quiescence, in 

 accordance with the seasons. Consequently the larger fringes on the 

 spiral shells of many mollusks, as well as the "shoots" of an oyster's 

 shell, afford satisfactory indication of the age of these creatures. An 

 oyster ;[ continues to enlarge his shell by annual "shoots" for four or 

 five years, and then ceases to grow except in thickness. The number 

 of spiny varices on the shells of the various species of Murex is never 



* Jour. M.B.A. i., 1890, pp. 447-50. 



t ■Woodward's Manual of MoUusca, 1880, pp. 12, 13, 213. 



X Oysters may produce spat when two years old, Ijut are most prolific in their fourth 

 and fifth years {ftde Hoek. See this Journal, N.S. i. p. 277). 



