Translation Series No.1211

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were caught with seines in Mar. Since they are not being fished at present,-
one must reckon with 1000 fish in the'region in question, these Must have
eaten at least 500 tagged fish.
Brook trout of a length of 23 to 33 cm are represented as the •
most important predators of salmon. These robbers retain the tags in their
stomachs for at least four months. Of the fish examined (total number un-
known), ,20 fish . contained 134 tags. Since the brook trout forms . a strong
stationary stock, one can reckon with 1000 fish, who consumed a total of
2000 tagged salmon.
With these minimum assumptions one obtains the number of 2800
tagged salmon that had been eaten by the predators cited. That corresponds
to a loss of 54 per cent in the estuary alone and principally within,four
months. As has been mentioned above, it is true that a series of parr have
been included in the investigations 16 .
7.3.2. The mortality until the beginning of exploitation
The above statements of the present paper show that the numbers
of salmon in the recruitment phase are being reduced quite heavily. With-
out doubt, the decisive losses take place during the period bêtween eMie
ration and the transition to pelagic fish food. The smolt at that time
constitute a' disturbing element in the equilibrium of the population mech-
anism of the-other dwellers in the sea. They are being forced to learn
an entirely new behaviour for their conduct in life. Instead of the pos.-.
sibilities of hiding that they had in the rivers, now only speed is of
avail against predators. The relations.between predator and prey have
16 According to Piggins, the smolt losses have to be set at 70 per oent
(personal communication).