FACTORS ASSOCIATED WITH RECRUITMENT OF SAUGERS IN TENNESSEE AND
CUMBERLAND RIVER RESERVOIRS, TENNESSEE, 1990-1997
Important seasonal fisheries exist for indigenous saugers Stizostedion canadense in
the
mainstream impoundments of the Tennessee and Cumberland Rivers, Tennessee; however,
extreme fluctuations in abundance of sauger populations result in cyclical fisheries.
Experimental
gill nets were used to collect sauger over eight years in four Tennessee River
reservoirs (Watts
Bar, Chickamauga, Guntersville, and Kentucky) and one Cumberland River reservoir (Old
Hickory) during spawning migrations (January - April). Between 1990 and 1997, 634
saugers
were collected from the Cumberland River and 3,179 were collected from the Tennessee
River.
Saugers ranged from age-1 to age-10; however, 97% of the saugers were less than age-4.
Due to
the absence of older saugers, all fisheries were dominated by saugers less than 400 mm
TL. Age-
1 and age-2 sauger catches were used as indices of recruitment in the Tennessee River
and
Cumberland River, respectively. Sauger recruitment was modeled as a function of the
amount of
water discharged and number of fingerlings stocked in previous years. Sauger recruitment
in two
upper Tennessee River reservoirs was related to total volumes discharged the previous
spring
(February to April; r>+0.91; P=0.0001); no significant relationship between spring
discharges and
recruitment was evident in two lower Tennessee River reservoirs or Old Hickory Reservoir
on the
Cumberland River. Current models suggest that February-April discharges between 8.4 x
109 and
15.4 x 109 m3 may enhance recruitment in the Tennessee River; whereas, discharges above
or
below this range are detrimental. Optimal discharges cannot occur simultaneously
throughout the
Tennessee River. Based on empirical relationships between discharge, recruitment, and
river
reaches, we concluded that strong recruitment throughout the Tennessee River cannot
occur in
the same year. Recruitment was not related to fingerling stockings in two upper
Tennessee River
reservoirs; however, age-2 sauger catches in Old Hickory Reservoir on the Cumberland
River
were related to the number of fingerlings stocked two years earlier (r=+0.99; P=0.0001).
Gonadosomatic index values were either zero for immature or spent male and female
saugers, or
>0.075 and >0.025 for mature female and male saugers, respectively. Total length (TL) at
maturity for female and male saugers was approximately 300-325 mm TL and 225-250 mm TL,
respectively. The 381-mm minimum size limit in the upper Tennessee and Cumberland River
protected 73-85% and 32-52% of mature male and female saugers, respectively. The 356-mm
minimum size limit in the lower Tennessee River protected 78% and 47% of the mature male
and
female saugers, respectively. Saugers collected in the upper Tennessee River were
significantly
older and longer, on average, than saugers collected from the lower Tennessee River in
most
years. The pooled average age of saugers in the Tennessee River over their eight-year
study was
1.99 years. We propose that mean ages falling outside the range of 1.5 to 2.5 years (+2
S.D) will
characterize populations suffering from over-exploitation or consistently poor
recruitment. |