PROBABILITY OF FIRST SEXUAL-MATURATION OF MALE PARR IN WILD SEA-RUN BROWN TROUT (SALMO-TRUTTA) DEPENDS ON CONDITION FACTOR 1 YR IN ADVANCE

In three years, in late autumn, underyearling wild sea-run brown trout (Salmo trutta) in a small stream were captured with electric fishing and tagged with microchips (passive integrated transponders). They were recaptured during the following season either as migrating smelts in a trap or by electric fishing in the stream just after the migration period and during spawning (late autumn). At spawning, they were distinguished as sexually mature male parr or immature juveniles. The smelts were longer and heavier at tagging than the mature male parr and the immature parr, which were similar in initial length and weight. The mature male parr had a significantly higher condition factor at tagging than the immature parr. The probability of parr maturation was positively associated with initial condition factor but not with initial body length. Growth of mature male parr and immature parr was similar in the early season but higher for immature parr in the late season. The result indicated that the choice of strategy was made earlier in life than previously recognized.