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Evaluation of Catch and Release Regulations
On Iowa's Maquoketa River

(Editor's Note: This Iowa Department of Natural Resources Report has been excerpted and edited for space and clarity.)

A catch and release regulation for smallmouth bass was put into efect on a 4.5 mile section of Iowa's Maquoketa Rvier in 1988. Yearly fish samples were conducted from 1987 (before imposition of the new regs) through 1992. Two control areas under the statewide 12 inch minimum size rules were sampled in 1992. Comparisions were also made with a smallmouth population study in 1980-82.

Weight of smallmouth bass increased significantly in the catch and release section during the 1988-92 period. The percentage of smallmouth over 12 inches also increased-- from 5% to 46%. Average annual mortality rate decreased from 53% in the 1980-82 period to only 24% in the 1988-92 period. In 1991, the smallmouth population was estimated at 899 fish, with 522 of these 12 inches or larger. Total weight of smallmouth was 36.0 pounds per acre. The population in the 1980-82 (pre catch and release) period was estimated at 933 fish, but only 128 of these were 12 inches or larger. Total weight of smallmouth during the pre-catch and release period was 11.2 pounds per acre (less than one third of the catch and release period).

Overall Assessment of the Maquoketa's Catch and Release Regulations:

  • The number of smallmouth over 12 inches increased dramatically
  • Relative weight of smallmouth increased
  • The overall number of smallmouth remained constant
  • Growth rates remained constant or slightly improved
  • Total annual mortality decreased
  • Increased numbers of adult fish had no apparent influence on year class recruitment

The extremely postive results of the Maquoketa River regulations were used as a rationale for the expansion of catch of release regulations to two other Iowa rivers, the Cedar and Upper Iowa.

Length-frequency of smallmouth bass sampled from the Maquoketa River catch
and release section, 1987 - 1992.

Length
(inches)
 1987 1988 1989 1990 1991 1992
5"
5
8
18
0
17
13
6"
2
52
30
1
9
69
7"
64
35
19
4
9
81
8"
61
27
21
17
2
32
9"
37
54
24
15
11
10
10"
13
50
18
15
50
5
11"
6
32
16
5
50
12
12"
3
8
6
8
32
21
13"
4
5
1
17
31
38
14"
3
3
0
9
24
37
15"
2
1
0
6
25
35
16"
0
2
0
2
32
20
17"
4
3
1
3
13
18
18"
0
3
0
1
4
5
19"
0
0
0
2
4
8
Total
291
300
164
105
417
443
%5 Over
12 Inches
5%
8%
5%
46%
40%
44%

Conclusions:

After 5 years of a catch and release regulation for smallmouth bass on the Maquoketa Rvier, all biological data indicated very positive results. While the overall population remained stable, the number of fish 12 inches or larger dramatically increased. This was achieved with an increase of relative weight, stable or increased growth rates, a decrease in total annual mortality and no apparent impact on year class recruitment.

During the same period that smallmouth densities increased, the stocking of northern pike and walleye fingerlings also resulted in an increase in the biomass of these two species. Largemouth bass numbers were also high due to their emigration from adjacent Lake Delhi. The increase in three other predator species did not appear to hamper the development of an extremely high quality smallmouth bass population.
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