Among the unusual products produced by Colorado Parks and Wildlife (CPW) staff is an annual crop of infant walleye. Producing these fish for the benefit of my fellow anglers provides a particularly gratifying feeling as walleye are Colorado’s second most sought after species to catch behind trout. Natural reproduction by this species is extremely limited thus a team of biologists, volunteers, hatchery personnel, and law enforcement descend upon two Denver metro reservoirs and Pueblo Reservoir to produce walleye each March. This year’s total statewide request was a hefty 100 million eggs, with an addition 20 million eggs requested in trade to neighboring states. The process begins by deploying more than a mile of gillnets at Cherry Creek, Chatfield, and Pueblo reservoirs each evening and soaking the nets overnight. The next morning, CPW crews return to remove the fish; the walleye rarely die because low water temperatures keep the fish from struggling much once they’re snagged. Walleye are attracted to the rock rip-rap along the particular reservoir’s dam; however the nets intercept the fish before the fish unsuccessfully attempt to spawn on their own. Once the holding tank on the boat is flush with walleye, the fish are transported back to the “barge” - a 32 foot floating monster where the walleye are off-loaded and sorted by sex. Video footage of the entire process can be viewed here:
Once all of the nets are removed from the dam, female walleye release their eggs by applying light pressure to the fish’s belly in the direction of a vent, located just in front of the tail. Next, sperm from a male walleye is added to the pan along with 1 gallon of water, to activate the fertilization process. After stirring the mixture for 90 seconds with a feather, a bentonite based fluid mixture of mud is added to prevent the eggs from clumping. The clumps are bad news for the eggs as each individual egg must be oxygenated in order to hatch. Finally the pan of eggs is rinsed with clean water and stored for later transport to a hatchery in Wray or Pueblo. After completing the spawn process all walleye are returned to the lake unharmed.
The hatch rate is a remarkable 80-85% with young walleye and saugeye emerging from the egg stage about 10 days after reaching the hatchery. Roughly 40 lakes and reservoirs in Colorado have already received the young fry while fingerlings walleye, grown to 1.5 inches, will be stocked around June 1. Fingerling saugeye and walleye have a better survival rate but limited hatchery pond space constrains fingerling production to about 1.5 million fish. The gap in fingerling production is met by simply stocking additional fry.
Walleye and saugeye fry are counted by volume at the Wray or Pueblo hatchery and placed in a plastic bag that is heat sealed and inflated with oxygen. Each bag typically contains 100,000 fish which are then placed in an insulated container resembling a pizza delivery box. Once at the lake the bag of fish is acclimated to the particular lake temperature and the fish are released in the middle or "upwind" of any wave action.
Top 10 Walleye/Saugeye Waters by numbers of stocked fry (M=million)
1. Pueblo Reservoir: 12.0M WAL
2. John Martin Res: 6.0M SAG
3. Jackson Reservoir: 5.7M WAL + SAG
4. North Sterling Res: 5.5M WAL + SAG
5. Cherry Creek Res: 4.0M WAL
6. Prewitt Reservoir: 4.0M WAL + SAG
7. Jumbo Reservoir: 3.2M WAL
8. Chatfield Res: 3.0M WAL
9. Aurora Reservoir: 3.0M WAL
10. Meredith Reservoir: 2.0M WAL
Top 10 Walleye/Saugeye Waters by number of stocked fingerlings
1. North Sterling Res: 62,000 WAL + SAG
2. Boyd Lake St. Park: 60,000 WAL
3. Trinidad Reservoir: 60,000 WAL + SAG
4. Narraguinnep Res.: 58,000 WAL (triploid/sterile)
5. Lonetree Reservoir: 52,000 WAL
6. Jackson Reservoir: 52,000 WAL + SAG
7. Martin Lake (Lathrop): 45,000 WAL + SAG
8. Brush Hollow Res: 36,000 WAL
9. Prewitt Reservoir: 26,000 SAG
10. Beckwith Reservoir: 25,000 WAL
*Note: the fry numbers listed above have already been stocked but the fingerling numbers represent what has been requested. The rearing ponds have been stocked at Pueblo for fingerlings production but thoise fish are not yet to size.
On the private sector 120 million walleye eggs would fetch roughly $4.0 million dollars. Because of the efficiency of all team members involved, public volunteers included, CPW staff can stock more than 80 Colorado waters at a fraction of that cost.
On the final day of this year’s spawn at Cherry Creek Reservoir the final tally for the 2013 season read 1,451 male walleye, 375 green females (fish not quite ready to release her eggs), and 352 ripe females were collected, virtually all of which measured greater than 17 inches. The 352 female fish provided 46.7 million walleye and saugeye eggs toward the statewide request. Total walleye mortality was once again minimal; out of the 2,047 walleye handled (Cherry Creek only), less than 50 perished. All nets and equipment were pulled off Cherry Creek, Chatfield, and Pueblo as a secondary peak in the eggs take was starting to take place. However, the goal of 120 million eggs has been reached and no additional tormenting was necessary that that point.
To date, all walleye and saugeye fry that hatched have already been stocked into Colorado waters, thus the 2013 spawn season is almost complete as actually getting the fish in the water ensures we have another year class out there. Go Fish Colorado!
Ben Swigle is an aquatic biologist with Colorado Parks and Wildlife stationed out of the Fort Collins office. Ben holds a BS in biology from the University of Notre Dame and a MS in fisheries science from the University of Nebraska-Lincoln. After working 2 years as a fishery biologist with the USGS in Oregon, he joined Parks and Wildlife in 2005. Ben specifically manages lakes, reservoirs, and streams within the Big Thompson, St. Vrain, and Boulder Creek watersheds.