Use of otolith microstructure to study life history of juvenile chinook salmon in the Strait of Georgia in 1995 and 1996

Abstract

The pattern of otolith daily increments was used to identify hatchery-reared, wild ocean-type and wild stream-type chinook and study their life history in the Strait of Georgia. In 1995 and 1996, almost all of hatchery-reared and wild stream-type chinook entered the Strait of Georgia in May and June, while wild ocean-type chinook entered from April to August. Upon ocean entry stream-type fish were the largest and wild ocean-type the smallest. Hatchery-reared and wild ocean-type chinook leaving fresh water later in the year were larger than those leaving earlier. The mean length of wild stream-type chinook was not related to the time of ocean entry. All the life history types maintained their size differences throughout the summer and fall despite some differences in rates of size increase. Hatchery-reared and wild stream-type chinook grew faster in 1995 than in 1996. Wild ocean-type grew at about the same rate. During early summer, the percentage of wild ocean-type chinook was low in contrast to the percentage of hatchery-reared and wild stream-type chinook in 1995 and 1996, respectively. In September of both years, the percentage of wild ocean-type chinook increased and the percentage of hatchery-reared and wild stream-type chinook dropped. By November in both years, the percentage of hatchery-reared chinook increased, especially in 1996 when the percentage exceeded 80%. After the first ocean winter, the percentage of hatchery-reared fish remained high.