Effects of parental and smolt traits on the marine survival of released Atlantic salmon (Salmo salar)

Abstract

Crossing experiment of sea-ranched Atlantic salmon (Salmo salar) was used to study the factors behind marine survival and precocious maturity of the offspring. The compared smolt groups differed in their parental rearing history (wild or reared), and also in their parental age at maturity. The length and potential precocious maturity of the smolts at the time of release was recorded. Altogether, about 18400 externally tagged smolts, derived from different crossing groups, were released into the estuary of the River Kemijoki, in the northern Baltic Sea, in 1986 and 1988. The total tag recovery rate was 15% for both year-classes. The results showed that the rearing history of the parents had a significant influence on both the survival and the precocious maturation of the offspring. Reared parents produced on average faster growing offspring than the wild parents. Precocious maturation reduced marine survival of the offspring in the first hatchery generation, but not anymore in the second hatchery generation. The marine survival of both immature and mature smolts generally improved with increasing smolt size, but still the large precocious males (over 21 cm) had the best survival. Maternal and paternal age at maturity and their interactions had also a significant influence on the survival and precocious maturation of the progenies. The increasing maternal and paternal age at maturity had opposite effects on precocious maturation rate of the offspring. Decreasing maternal age and increasing paternal age both increased the proportion of precocious males among the offspring. The survival of the precocious male offspring of old females (3 sea-winter) and young males (1 sea-winter) surpassed all other offspring groups. The proportion of these precocious males was, however, low consisting only 2% of all offspring. Maternal sea age was more important than maternal rearing history in determining marine survival and precocious maturation of the offspring. Survival was higher and precocious maturation was less frequent for the progenies of older females compared to those of young females. The results as a whole suggest that an increased number of hatchery generations do not necessarily reduce the marine survival of sea-ranched Atlantic salmon, but hatchery rearing may generate selection, which causes significant genetic changes in life history traits, even in one hatchery generation.