Cheyenne River, rainbow smelt became less important and the diet of walleyes was primarily comprised of freshwater drum (Aplodinolus grlUlllie1Lf), yellow ...
/I/f?-/ 331
Changes in Walleye Food Habits Throughout Lake Oahe, South Dakota, in August 1991 JEFFREY J. JACKSON, DAVID W. WILLIS, and DAVID G. FIELDER _.
Deparunent of Wildlife and Fisheries Sciences, South Dakota State University, Brookings, SD 57007 (JJJ. DWW) South Dakota Department of Game, Fish and Parks, 523 East Capitol, Pierre, SD 57501 (DGF) ABSTRACT - Walleye (Slizosledion IIitrelUll) food habiu were detennined at nine sites throughout the South OakOIa ponion of Lake Oahe in August, 1991. Walleyes were primarily piscivorous; however, food habits varied among walleye length groups and Ihroughout the reservoir. Consumption of rainbow smelt (Osmerus mordax) was limited to three sites in the lower ponion of Lake Ow. Above the Cheyenne River, rainbow smelt became less important and the diet of walleyes was primarily comprised of freshwater drum (Aplodinolus grlUlllie1Lf), yellow perch (ferCiJ fUlIIeSCe1Lf), and white crappies (PomoxisaMularis). Macroinvertebrates were not a substantial ponion of the diet of walleyes in August. Walleyes preyed predominantly on ageoO fishes except at Peoria Flats and Cow Creek, where adult rainbow smelt were consumed.
Key words: Sliumedioll vitrelUll, walleye, food habiu, Lake Oahe, South OakOIa
Lake Oahe is a 126,OOO-ha mainstem reservoir on the Missouri River. The maximum depth of the reservoir ranges from 56 m in lower Lake Oahe (near the • dam) to 15 m at the upper sites (Selgeby and Jones 1974). The reservoir stratifies thermally with the strength and duration of stratification greatest near the dam (Selgeby and Jones 1974). Burczynski etal. (1987) found that in August rainbow - smelt (Osmerus mordox) occupied only the hypolimnion in these stratified areas. The Lake Oahe prey fish base is comprised predominantly of rainbow smelt. spottail shiners (Nolropis hudsonius). emerald shiners (Notropis anlherinoides). yellow perch (Percajlavescens). white crappies (Pomoxis aMularis). and freshwater drum (Aplodinotus grUMiens) (Johnson et aI. 1992). The purposes of this study were todetennine how walleye (Slizosledion vitreum) food habits changed throughout the reservoir in August. and to evaluate the importance of individual prey fish in the diet of walleyes.
Prairie Naturalist 25(4): December 1993
332
MATERIALS AND METHODS
We collected walleye stomach samples during the annual fish population survey conducted by the South Dakota Department of Game, Fish and Parks in August 1991. Walleyes were collected with nylon multifllament mesh gill nelS at nine fixed sites distributed throughout the South DakOla portion of Lake Oahe (Johnson etal. 1990, 1992) (Fig. 1). Gill net dimensions were 91.4 m x 1.8 m, with
South
Figure 1. Gill netting stations at which walleyes we.e collected for food habits analysis from Lake Oahe, South Dakota, in August 1991.
Jackson, Willis, and Fielder: Walleye Food Habit5
333
I5.2-m panels of the following bar mesh sizes: 13, 19,25,32,38, and 51 mm. Six gill nets were set on the bottom and fished overnight (approximately 20-24 hr) at each site, with three nets set from 0-10 m and three from 10-20 m.
Walleyes were measured (total length) and the stomach excised and preserved in formalin. Stomach contents were flushed into a petri dish, and prey organisms were counted and identified to the lowest necessary taxon using keys by Merritand Cummins ( 1984),Pennak (1989), and Eddy and Underhill (1978). When possible, prey fish were identified as age 0 or age 1 and older. Yellow perch and rainbow smelt were identified as age 0 at total lengths less than or equal to 75 and 55 mm, respectively. Overall dry weight for each prey taxon, excluding zooplankton, was determined for each stomach. Samples were dried at 60°C for 24 hr in a drying oven. - Zooplankton lengths were measured using a digitizing pad and a computer software program (Daniel B. Hayes, National Marine Fisheries Services, Woods Hole, MA, pers. common.). Length-to-dry weight regressions (Bottrell et al. 1976) were then '\I used to approximate the dry weight of each zooplankton taxon. We evaluated food habits as percent by weight (PBW) for each prey taxon by each walleye length group. Walleye length groups were 10-18, 18-31,31-41, and greater than 41 cm. These length group separations were used because they depicted the age distribution for age-O, age-I, age-2and age-3 and older walleyes in the lower portion of Lake Oahe (Johnson etal. 1992).
RESULTS We sampled 1402 walleyes from the nine sites on Lake Oahe in August; of these, 346 (25%) contained identifiable prey (Table 1). Pollock Age-O walleyes (10-18 cm) preyed predominantly on Leptodora (pBW=99) • at Pollock (Table 1). Freshwater drum were important for most other walleye length groups. Although ephemerids and chironomids appeared to be important for walleyes that were 18-31 cm, this may have been the result of a small sample size. Grand River White erappies were the primary prey for most walleyes at the Grand River site (Table 1). However, white crappies became less important for walleyes 31-41 cm and greater than 41 em, and freshwater drum and age-O yellow perch were the predominant prey. Blue Blanket
Walleye food habits at Blue Blanket were similar to the Grand River in species composition, with freshwater drum, white crappie, and yellow perch predominating in the diet (Table 1). Age-O yellow perch became increasingly important for
Table 1. Percent by weight of prey consumed by length (em) groups of walleyes collected from lake Oahe, South Dakota in t: August, 1991; percent by weight values of 0 are 41
POl
10-18 18-31 31-41 >41
GRR
10-18 18-31 31-41 >41
BLB
10-18 18-31 31-41 >41
MOR
10-18 18-31 31-41 >41
WHB
7 2 16 2
6
20
26
11
8
5 2
10 100
6 4 5 4 8 37 6 0
12
44
99
o
o
o
3
4
19
80 100
12
24 25 3 3
1 94
46 48 13 5
66 74
17
39
49
61 15
14 27 52
8
o
2
o 43
84 100 75 47 48 5 40
11 25 32
21
49
3
83 6
o
7 50
2
.
5 2
o
~
'iii n
""IS
2
Table 1. (cont.) Length
Site
10-18 18-31 31-41 >41
BUS
10-18 18-31 31-41 >41
CHR
10-18 18-31 31-41 >41
CDC
10-18 18-31 31-41 >41
PEF
N
WHB
FWD WHC
YEP1
YEP2
EMS
STS
RBS1
RBS2
5MB
IDD
EPH
CHR
LEP
DAP
DIA
~ Fa· I»
0 20 22 1 19 6 6 2
J
27 9
71
15 12
2 1 100 21 35 5 13
2
27
13
c.. ....,
0
8 64
iir
c: ID
0
~
0
78 10
[ 98
0
2
100 100 100
8
~
iii ~
30
25 24
87
16 15 9 1 10 17 12 8
19
100 8
83 100 100
0
~
ij-'
0
0
1-'80 0 200Aae 1 and older
w w
V'I
336
Prairie Naturalist 25(4): December 1993
walleyes less than or equal 10 41 em. For walleyes greater than 41 cm, white bass and adult yellow perch were the primary prey. Age-O walleyes consumed primarily white crappie (pBW=61). with zooplankton (Leptodora and Daphnia) being of secondary importance. Moreau River White crappies were the predominant food item for all walleye length groups at the Moreau River site (Table 1). Other fISh species were of minor importance. This was the only location other than the Cheyenne River where walleyes preyed on smallmouth buffaloes (Ictiobus bubalus). and they were only found in walleyes greater than 31 cm. Whitlock's Bay Whitlock's Bay was theonly location on Lake Oahe where macroinvertebrates were found in the diet of most walleye length groups (Table 1). All length groups had similar food habits, containing white crappies, age-O yeUow perch, and ephemerids. Age-I and older yellow perch were only important for walleyes 31-41 cm. Walleyes sampled that were greater than 41 cm contained no identifl8ble prey. Bush's Landing The Bush's Landing site was a transition area along the main river channel. Food habits were diverse, and this site was the furthest up the reservoir that rainbow smelt consumption was observed (Table I, Fig. 1). There were no age-O walleyes sampled at this site and only one walleye greater than 41 cm. The remaining two length groups had similar food habits, with white bass (Morone chrysops), age-O yellow perch, and age-O rainbow smelt predominating; however. age-l and older rainbow smelt composed a higher proportion of the diet for walleyes that were 3141 cm. This was the only location whereage-O rainbow smelt were found in the diet of walleyes that were greater than 31 cm. Cheyenne River All length groups of walleyes preyed on freshwater drum (PBW ranged from 5-35) at the Cheyenne River site (Table 1). Walleyes that were 10-18 cm preyed predominantly on white crappies (pBW=78), with freshwater drum being of minor importance. The three larger length groups had similar food habits, each containing freshwater drum and yeUow perch. Age-l and older yellow perch become increasingly important for larger walleye length groups. Smallmouth buffalo appeared in the diet of walleyes 18-31 cm, and white bass were important for walleyes 31-41 em (pBW=71). Peoria Flats and Cow Creek Rainbow smelt were the most imponartt prey consumed by all length groups of walleye at Peoria Flats and Cow Creek (Table 1). Walleyes that were 10-18 cm
Jackson, Willis, and Fielder: Walleye Food Habits
337
primarily consumed age-O rainbow smelt at both locations. At Peoria Flats. the diet of 18-31 cm walleyes was more diverse than at Cow Creek and included age-l and older rainbow smelt(pBW=78).age-Osmelt(pBW=8),age-Oyellowperch (pBW=8), and some macroinvertebrates. In both locations, the diet of walleyes greater than 31 cm consisted entirely of age-l and older rainbow smell DISCUSSION We found that walleyes at all sites were primarily piscivoreus in Lake Oahe in August, which corresponds to conclusions drawn by most authors (Forney 1974. Swenson 19TI. Colby etal. 1979,Knightetal.1984,Mero 1992). Macroinvertebrates were not a substantial part of the diet of walleyes. At Whitlock's Bay, the occurrence of macroinvertebrates in the diet of walleyes was probably due to ephemerid distribution. Swanson (1967) reported that Hexagenia were primarily • located in bay areas that lacked current in Lake Sharpe, South Dakota, on the Missouri River. Rainbow smelt occurred in the diet of walleyes at three sites on the reservoir. In August, these areas were the only sites where water temperatures were within the range (5· 14°C) preferred by rainbow smelt (Burczynski et al. 1987). Mere (1992) found that rainbow smelt were the most important prey of walleyes near the dam at Lake Sakakawea. North Dakota, in August but were less important further up the reservoir. He attributed the decreased importance of rainbow smelt to an increased diversity of the prey base, turbidity, and water temperatures. In Lake Oahe, the increased importance of age-O rainbow smelt in the diet of walleyes at BUS could be due to a lower abundance of adult smelt, or there may have been differences in the distribution of age-O smell Stone and Burczynski (1991) found that age-O rainbow smelt were more abundant in trawl samples above the Cheyenne River compared to lower Oahe. Zooplankton wereooly preyed upon by walleyes that were 10-18 cm and then primarily at sites in upper Lake Oahe. Generally, piscivory is initiated when walleyes are between 30 and 60 mm in total length (Bulkley et al. 1976, Johnson et . al. 1988. Jackson et al. 1992). In Escanaba Lake, Wisconsin, the growth of age-O walleyes was inhibited when zooplankton were a substantial part of their diet after a total length of 60 mm (Morsell 1970). Young-of-the-year fishes were the predominant item preyed upon by all walleye length groups in Lake Oahe in AuguSL However, stomach samples were primarily obtained from walleyes less than 41 cm. Parsons (1971) and Knight et al. (1984) found that walleyes were size-selective predators, which would govern the maximum length of prey fish available to walleyes; thus, the importance of age-l and older fishes for larger walleyes may not be represented. Yellow perch were consumed by aU length groups of walleyes at sites above the Cheyenne River. Other studies of walleye food habits have indicated the importance of yellow perch (parsons 1971, Forney 1974, Nielsen 1980). In Lake
338
Prairie Naturalist 25(4): December 1993
Oahe, age-l and older yellow perch were primarily important prey for walleyes
greater than 31 em. White crappies and freshwater drum were also consumed by walleyes at and above the Cheyenne River. As with yellow perch, most white crappies and freshwater drum consumed by walleyes were age O. Notropis spp. were not important prey for walleyes in Lake Oahe in August This was unexpected because spottail and emerald shiners were abundant in seine samples collected in August (Johnson et al. 1992). Because this was a one-time sample, the importance of these species during other months is unknown. Swenson (1977) found that electivity for Notropis spp. was negative during periods of high yellow perch abundance and positive or zero during reduced perch abundance in Lake of the Woods and Shagama Lake, Minnesota. Knight et al. (1984) found that electivity values for spottail and emerald shiners were positive in the spring, but values varied from -1.00 to 0.66 during summer and autumn in western Lake Erie. We found that walleye food habits varied substantially among sites on the reservoir. Some of this variability may be due to differences in prey fish distribution, which are additionally impacted by the thermal characteristics of Lake Oahe. A more thorough evaluation would determine walleye food habits throughout the year to evaluate seasonal changes in food habits along with the differences throughout the reservoir. ACKNOWLEDGMENTS
We would like to thank Wayne Plucker, Danny Isaak, Tracy Hill, and South Dakota Department of Game, Fish and Parks personnel for their assistance with data collection. Manuscript review was provided by Steven Mero, John Lott and Christopher Guy. This paper was approved for publication by the South Dakota Experiment Station as Journal Series 2700. Partial funding for this project was provided by the South Dakota Department of Game, Fish and Parks through Federal Aid in Spon Fish Restoration Project F-15-R-1544. LITERATURE CITED
Bottrell, H.H., A. Duncan, Z.M. Gliwicz, E. Grygierek, A. Herzig. A. HillbrichtIlkowska, H. Kurasawa, P. Larsson, and T. Weglenska. 1976. A review of some problems in zooplankton production studies. Norw. J. Zool. 24:419456. Bulkley, R.V., V.L. Spykermann, and L.E. Inmon. 1976. Food of the pelagic young of walleye and five cohabiting fish species in Clear Lake. Iowa. Trans. Am. Fish. Soc. 105:77-83. Burczynski. J J .• P.H. Michaletz. and G.M. Marone. 1987. Hydroacoustic assessment of the abundance and distribution of rainbow smelt in Lake Oahe. N.
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339
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Swanson. G.A. 1967. Factors influencing the distribution andabundance of Hexagenia nymphs (Ephemeroptera) in a Missouri River Resecvoir. Ecology 48:216.225. Swenson. W.A. 1977. Food consumpion of walleye (Stizostemon vitreum vitreum) and sauger (S. canadense) in relation to food availability and physical conditions in Lake of the Woods. Minnesota. Shagawa Lake. and western Lake Superior. J. Fish. Res. Board Can. 34:1643-1645.
Received 21 December 1992. Accepted 3 August 1993.
