RAPPORT 1905—06 ANNEXE C OR 
six months the bottles become anchored, and cease to move. Dr. AzrEN has suc- 
ceeded in obtaining the return of several unopened bottles, and these show good 
reason for their anchoring, in the weight of barnacles and other organisms en- 
crusted upon them. In our preliminary experiments in the Plymouth Aquarium 
Dr. ALLEN and I proved that a very small increase in the dead-weight is sufficient 
to anchor the bottle against even a very strong current’). 
In these returned bottles the end of the wire is ground uniformly to a fine 
conical point, from the dragging through the sand. 
Until the movements of the bottles have been worked out with considerably 
greater detail, the most interesing result is undoubtedly the large number reco- 
vered. The evidence which I have been able to examine appears on the whole 
to favour the supposition that the percentage of bottles in a given area recovered 
by the trawl does not differ largely from the percentage of plaice of 21-26 em. 
in the same area caught by the trawl in the same time. But whatever view may 
be held as to the ratio between recovery of bottom-trailers and destruction of 
plaice, the statistics of bottle-recovery give a certain lower limit for the absolute 
measure of the intensity of trawling. 
In Series A in the first twelve months 221 out of 390 bottles were recovered, 
or .57. If we neglect the first 21/2 months as being exceptionally high, owing to 
the fact that the bottles were deliberately dropped where much trawling was going 
on, the following period of six months shows 90 recovered out of 280 in the sea 
at the beginning of the period, a ratio of .32 for the six months or .54 for the 
year [(1 — .32)? = (.68)? = .46 = 1—.54]. In Series B, in the first twelve months, 
158 out of 270 were recovered, or .59. If we neglect the first 21/1 months, the 
next six months shows 66 recovered (by trawling only) out of 197 in the sea at 
the beginning of the period, a ratio of .34 for the six months or .56 for the year. 
These two experiments, therefore, are very consistent in showing that im the 
Southern part of the North Sea (mainly south of latitude 54°30’), the annual rate 
of collection of inanimate catchable objects by trawlers is greater than 54 per 
cent of those exisling on the bottom at the beginning of the year. Series C shows 
in nine months, out of 129 bottles put in, 27 bottles cast up on the shore, and 31 
recovered in trawl-nets. The latter figure gives .24 for nine months, which is the 
equivalent of an annual rate of .31, or 31°/o, but from the large number of bottles 
found on the shore it seems probable that a larger number were cast up and lost. 
It should be noted, however, that these figures indicate less than the true 
1) Reserving definite statement until after more exact study, there appears in each expe- 
riment to be a tendency for many of the bottles, after being in the water six months and up- 
wards, to segregate in the neighbourhood of lat. 54° N., long. 3° and 4° E. This may indicate 
slack water, or merely rough ground and barnacle-spawn. 
a in 
