Michigan Department of Natural Resources
Fisheries Research Report No. 2029, 1996.
Age and Growth of Chinook Salmon in Lake Michigan:
Verification, Current Analysis, and Past Trends
Jay K. Wesley
Abstract.-Chinook
salmon Oncorhynchus tshawytscha from the Lake Michigan sport
fishery were studied to determine if changes in age and growth
occurred with recent forage shifts from alewife Alosa
pseudoharengus to bloater chub Coregonus hoyi. A decrease
in growth may indicate that forage shift stress caused the outbreak
of bacterial kidney disease (BKD) Renibacterium salmoninarum.
Known age chinook salmon implanted with coded-wire tags
were collected in 1994 to validate aging techniques and to compare
growth between fish collected by anglers and gill nets. Scale and
vertebra aging were 95.6% and 93.9% accurate, respectively. There
were no differences in age, gender, and maturity specific mean back
calculated lengths (mm) between harvest gears. There was also no
difference in mean back calculated length between sexes; however,
immature age-0.2 fish were smaller than mature age-0.2
fish. Mean back calculated total lengths and Fulton Indices of
condition were used to analyze historic growth using data and scales
from the Michigan Department of Natural Resources Lake Michigan Creel
Survey from 1983 to 1993. Average age decreased from a high in 1986
of 2.59 years to a low of 1.53 years in 1993. Mean length and
condition declined recently for age 0.1. Mean length increased from
1983 to 1993 for age 0.3. Condition increased after BKD for age 0.3
and 0.4 chinook salmon. The increase in length and condition of age
0.3 and 0.4 chinook salmon may be a competitive release and/or size
differential mortality in response to BKD. A reduction of chinook
salmon stocking in Lake Michigan might restore growth and reduce
mortality associated with BKD.