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— XRXVI — RAPPORT 1905—06 ANNEXE C 
intensity of trawling. Analysis of the returns shows a progressive decrease in the 
proportion recovered each month of the bottles yet unaccounted for, and this is 
very marked after six or eight months. The explanation is easy, since, with the 
knowledge that bottles, after being in the sea for a certain period, must anchor 
from the accretion of weight on them, it is obvious that a cerlain percentage must 
come to rest in rough and otherwise untrawlable spots, whence nothing but a 
cataclysm can restore them to observation. Certainly many trailers of Series B are 
settled in the Oyster Ground, some probably sunk in the Skager Rak depths while 
bottles from Series A must be distributed over almost every rough area of the 
Southern part of the North Sea‘). The following summary shows this progres- 
sive diminution, the returns are divided into an initial period of 5 and 6 weeks 
respectively, followed by equal periods of four months each. It will be seen that 
in Series A the percentage recovered from May to August 1906 is half the percen- 
tage recovered for the same months of 1905, indicating that of the 128 bottles 
unaccounted for on May Ist, 1906, only about 60 were really attainable. Simi- 
larly in Series B it would appear that by March ist, 1906, about 50 bottles had 
disappeared, and by July ist perhaps 80 bottles. No doubt some of the missing 
bottles in this series were cast ashore, and in Series G it seems probable that 
some 40 bottles were cast ashore and not found. 
Again, the high percentages of the first few weeks in Series A and B are in 
no sense errors, but indicate a most important economical fact — that the fishing- 
vessels congregate where the fish are known to be, and there fish them so inten- 
sely that 20°Jo or 25°/o of the whole migrating shoal may be trawled up in a 
month and a half (assuming that a plaice of the size composing the shoal is as 
easy to catch as a trailer). The trailers do not migrate with the fish, and there- 
fore the annual rate of trawling indicated by the bottle-returns is considerably less 
than that to which the plaice are subject. The young plaice which straggle apart 
from the main bodies, in times or areas where they are too rare to be worth 
fishing for, will escape from this intense fishing, but so far as the new generation 
of sizeable plaice can be followed in its migrations and fished at the rate of 20 %/o 
in a month and a half, it will at the end of six months, be reduced to 2/5 of 
its initial numbers, and if the process be supposed to continue for the whole 
year, to 1/6. 
1) As provisional figures, I have arrived at the estimates that on the flat shores of Holland 
etc. about one third are found of the total bottles there cast ashore; and that of the bottles 
trailing on the bottom of the sea about one sixth, in the course of a twelve month, anchor in 
inaccessible places or otherwise disappear. 
