51813_Sturgeon biodioversity an.PDF

Table1. Estimates ofthesize ofthe lake Shown inparenthesesare
the 95% confidence intervals

sturgeon population from different sections of the Menominee River.

Year of population estimate

1970 1978 1970 1990 199 I

Low er section 893
(457-1329)
Grand Rapids section 2834 3201
(1729-3939) (2526-3876)

White Rapids section^2865 27493156
(2299-3430) (1997-3501) (2512-3800)

July or August. All sturgeon captured in 1990 and
1991 were measured in both total and fork length
(TL and FL, respectively) to the nearest centimeter,
but prior to 1990 only total length measurements
were taken. A representative sample of sturgeon
were weighed Capture-mark and recapture pop-
ulation estimates were made using the adjusted Pe-
terson estimator (Ricker 1975). Separate popula-
tion estimates were made for each of the three sec-
tions of river. Fish from both the initial and recap-
ture runs were collected with the electrofishing
gear. Recapture took place seven to ten days after
the initial run. All sturgeon ≥ 25 cm TL were includ-
ed and were tagged with either a Monel metal tag in
the base of the dorsal fin or with a Floy dart tag in
the caudal fin or with both. Because the number of
fish recaptured in the various size groups was not
large enough to make unbiased estimates, the num-
ber of fish actually sampled in each 2.5 cm size
group was used to estimate the fraction of the total
population in each size group. This method assumes
that capture efficiencies are equal among the vari-
ous size groups. Although this method does not al-

Table 2. Estimated number of lake sturgeon in the White Rapids

section of the Menominee River, by size group.

TL (cm) 1970 survey 1978 survey 1990 survey

< 107 2680 2543 2423

> 107 185 206 733

> 127 115 105 320

> 140 57 45 121

> 152 20 9 53

> 165 2 0 9

low one to calculate confidence intervals around

the estimates, it is the best estimate possible given

the data available.

Legal harvest of lake sturgeon by sport anglers on

the Menominee River only occurs during a two

month fall season. Since 1983, licensed anglers have

needed a special permit to fish for lake sturgeon in

all Wisconsin waters. In 1974, a minimum size limit

of 127 cm was imposed; prior to that time a 107 cm

size limit had been in effect. In 1992, the bag limit

for an angler was reduced from 2 fish season-1 to I

fish season-1. All legal fish taken in the sport fishery

must be registered and tagged at a Department of

Natural Resources approved station. All fish har-

vested are measured, weighed and checked for tags

at that time. Harvest inform ation from thc vai-ious

tion system.

Angler exploitation for the various sections of

river was obtained by calculating the average an-

nual harvest from registration data and dividing it

by the estimated number of sturgeon over 127 cm

sections of river wasobtained through this registration

Table 3. Estimated number of lake sturgeon in the Grand Rapids

section of the Menominee River, by size group.

TL (cm) 1979 survey 1990 survey

< 107 2584 2867

> 107 250 334

> 127 125 91

> 140 3 7 24

> 152 22 3

> 165 0 0

River section