Translation Series No.1211

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experiment were about 40 per cent and 60 per cent, respectively (1958 to
1960). . •
It is.possible to recognize the effect of fishing rather more
unambigUously, when adult salmon have been tagged in the sea. Blair (1955)
tagged in June 1940 6.8 salmon and 386 grilse in the sea near Newfoundland.
After one year 41.2 per cent of the salmon were recaptured and 1.5 per cent
in the second year. For grilse the corresponding figures were 36.6 per cent
(1st year), 2.6 per cent (2nd year) and 0.3 per cent (3rd year). Belding
arid Préfontaine (1961) tagged in June 1938 195 salmon at the northeast
6(0
coast'of Newfoundland, of which 21.8 A were reported back. Along the Irish
coasts 4562 salmon and grilse have been tagged between 1948 and 1961. The
average rate. of recapture was 26.4 per cent (A. E. J. Went 1964). In Nov-
ember 1960 and in December 1962 we have tagged on board of salmon cutters
86 salmon of the sea year class A.1+ and 13 fish of the sea year class A.+.
During tlie first year 18.6 per cent of the older fish were . reported from
the Baltic Sea and 9.3 per cent from rivers or their estuaries of the Gulf
of Bothnia. The recaptures of the gmall fish amounted to 15.4 per cent in
the Ilaltic Sea during the first year. A division of the larger salmon int o .
those that were liberated in good condition and others that were in medium
condition when liberated, gives for the first group 20 per cent recaptures
from the Baltic Séa and 13.3 per cent from the rivers. This material by
*itself is too small for the derivation of the mortality coefficients. It
may, however, be of some value for comparison with other results.-Wé obtain
(Pss
the wes4e through fishing with the aid. of a proportion (Beaverton and Holt
1957). The total number of thé dead stands in the same proportion to the
number of captured fish as the total mortality.to that caused by fishing.
No-Nt Z
F
11 . number at the time t 0 -
Nt = number at the time t..