Pw. Seelbach, POPULATION BIOLOGY OF STEELHEAD IN A STABLE-FLOW, LOW-GRADIENT TRIBUTARY OF LAKE-MICHIGAN, Transactions of the American Fisheries Society, 122(2), 1993, pp. 179-198
I examined the characteristics and dynamics of a population of wild st
eelhead Oncorhynchus mykiss in the Little Manistee River, an extremely
stable-flow, low-gradient (sandy) tributary of Lake Michigan. I monit
ored autumn parr populations by electrofishing (1981-1983), and I moni
tored spring emigrant populations at a weir near the river mouth (1982
-1984) and both autumn- and spring-returning adults at this weir (1979
-1987). Relative to other Great Lakes populations, steelhead in the Li
ttle Manistee River had several notable characteristics that are proba
bly linked to abundant groundwater and stable flows: (1) high abundanc
es of age-1 parr, smolts, and adults, (2) constant autumn age-1 parr d
ensities, (3) few emigrant parr, (4) fast growth when in the stream en
vironment, and (5) relatively late age at maturity (after 3 years in t
he lake). An excessive sand bed load occurs in the low-gradient sectio
ns of the river, limiting gravel spawning areas to higher-gradient sec
tions. This limited spawning area likely caused the relatively low abu
ndance of age-0 parr, and may also be a factor in late age at maturity
. Abundance and age structure of returning adults varied because of (1
) variable survival during the presmolt winter (13-90%), (2) variable
survival from smolt to maiden adult (6-29% for spring-run maiden spawn
ers), and (3) variable survival to repeat spawn (3-58%). Most adults r
eturning from a marked smolt cohort originated in the Little Manistee
River (mean +/- 95% confidence limit, 71 +/- 28%). Management of such
populations needs to focus on protecting and enhancing the stream envi
ronment, and on managing sport harvest. Modeling population dynamics w
ill require development of long-term data sets.