PRESIDENTIAL ADDRESS. 501 
of fishing which if continued would give us between 80 per cent. and 90 per 
cent. of recaptures in a year. 
Marked fish which have been liberated and yeciptured tell the same 
story of intensity of fishing. 
The intensity of fishing as indicated by the percentage of recaptures 
within twelve months of liberation is shown by the following table * :— 
Percentage 
Off shore Fish undér 25 cm, Over 25 cm, 
Dutch coast . : : = 23°7 20°3 
Deep water, Southern Bight : 13:0 26°6 
Leman Ground (liberated April and May) 18:7 17-4 
Leman Ground (liberated December) . — 21:0 
Horn Reef outer ground . ‘ : : 33:3 23:0 
Obviously, since some fish are known to have been captured but not 
returned to the laboratory, the method gives a minimum estimate. 
By applying the same method to the marking experiments of other 
countries as well as our own, Garstang”* gave the percentage recovered 
within twelve months of liberation of fish over 25 cm. in length as from 
4 per cent. on the Fisher Bank to 56 per cent. in the Skager Rak. 
When we reflect on the chances of these marked fish dying or being eaten 
or losing their labels, it is surely a most remarkable fact, full of significance 
to the practical man, that in the North Sea marked fish of marketable size 
are recaptured at the rate of between 20 and 30 per cent. each year, and 
sometimes at a greater rate. It would seem that each square yard of the 
fishing grounds is swept by the trawl not once, but again and again each 
year. 
Mr. Borley has conducted a large series of experiments to determine 
the vitality of fish after they have been captured by both the beam and 
the otter-trawl. It was necessary to determine the degree of injury caused 
by the actual trawling, the raising of the trawl, and the subsequent expo- 
sure on deck. The larger fish of both sexes were capable of resisting the 
damage to a greater extent than those of smaller size, and the relative 
resistance of the two sexes varied at different sizes, the male showing a 
decline in the increase of its vigour as it approaches maturity. One factor 
which is very deleterious to the fish is the presence of jellyfish in the trawl ; 
these either smother the fish or possibly sting them to death; at any rate, 
the mortality of the fish is enormously increased when medusae are present 
in any numbers. The otter-trawl is also far more harmful than the beam- 
trawl, and exposure on deck to a hot sun is another constant source of 
death, one hour’s such exposure in one series of experiments killing 99 per 
cent. of the smaller fish. In the ordinary commercial operation of trawling, 
whilst the fish are being sorted those that have no market value lie about 
on the deck of the vessel for at least an average period of one hour ; hence 
it is extremely probable that when shovelled overboard practically all are 
dead or dying. 
The work which has been done by our own special steamer has been 
supplemented by records carefully kept by certain selected captains of 
commercial trawlers, which sail from Grimsby or from Lowestoft. In this 
way the details of some 20,000 hauls have been examined, and their results 
tabulated by Miss Lee. 
I have left myself no time to describe the important hydrographical 
investigations carried on by Mr. Mathews into salinity, temperature, etc., 
which show us the conflicting currents at the mouth of the English Channel 
‘ Garstang, North Sea Fisheries Investigation Committee Southern Area, Report 
No. 1. 
2 Provisional Report on the Natural History of the Plaice (Committee B), 
Procés verbaux, vol. iii, 
