272 THE PLACUK OF OCTOPUS ON THE SOUTH COAST, 



of the sea along the whole English coast from Start Point to the Straits 

 of Dover is very slightly in excess of 52° Eahr., as recently determined 

 by Dickson;* whereas west of that line the mean annual temperature 

 of the coastal waters on the English coast rises from 52°*1 at the Start 

 to 53°'9 in the Scilly Isles. 



On the Erench coast the mean temperature is naturally somewhat 

 higher than the temperature even of Devonshire and Cornish waters, 

 and is not usually subject to so much depression during the winter 

 months. It is probably this difference which, more than any other, 

 renders impossible the permanent acclimatisation on the Devonshire 

 and Cornish coasts of animals which are common on the opposite 

 shores and rarely found on our own. The warm summers and mild 

 winters which we have recently experienced have enabled the octopus 

 temporarily to maintain themselves on our shores under pressure of the 

 exceptional circumstances prevailing on the Erench coast; but the 

 normal conditions of temperature will, in all probability, reassert 

 themselves during the next year or two, in which case the disappearance 

 of the octopus will almost certainly ensue. 



Great damage to the shell fisheries may unfortunately take place in 

 the meantime, and it is very desirable that the situation should be 

 carefully considered. If the figures given in Table I., p. 265, afford any 

 indication of the injury done to the fisheries in other localities as well 

 as Plymouth, the question arises whether it would not be better for 

 the fishermen to suspend all fishing for crabs and lobsters during the 

 continuance of the plague, and to turn their attention temporarily to 

 other kinds of fishing. By continuing to set their baited pots for shell 

 fish they will obtain very meagre catches of uninjured crabs and 

 lobsters so long as the octopus abound, and will at the same time 

 place a far larger number at the mercy of the octopus without any 

 chance of escape. As shown in Table I., fourteen out of every seven- 

 teen crabs and lobsters caught in October fell victims to the octopus, 

 whereas if they had not been imprisoned in the fishermen's pots they 

 would have been free to avail themselves of their natural methods of 

 concealment and protection. Many of those which are now killed in 

 the fishermen's pots would doubtless survive under natural conditions 

 until the octopus disappear again, and would thus add to the breeding 

 stock next year. It is to be feared that this stock, as well as the 

 abundance of young crabs, must have been seriously reduced during 

 the past summer. It is consequently to the fishermen's own interests 

 to avoid all unnecessary waste of those which remain, since it is on 

 them that the fisheries depend for their replenishment during the 

 coming years. 



* H. N. Dickson, Q. J. R. Mel. Soc., xxv., Oct., 1899. 



