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!
IceFishingFool, CO 4/23/2013 11:40:38 AM
Good news, and Thanks to all.
Reifer, CO 4/23/2013 11:50:41 AM
Very nice write up. I enjoyed it. where do we look to see the numbers stocked by lake over the past few years?
nightangler, CO 4/23/2013 12:33:49 PM
Awesome article!!! Thanks to everyone's hard work making it so we can keep catching eyes in CO!!!!
Ben Swigle (Swigs), CO 4/23/2013 1:58:46 PM
Reifer....whats your email.
Fishful Thinker, CO 4/23/2013 2:02:11 PM
Thanks Swigs for all your efforts, and for sharing your info here! CL
opencage, CO 4/23/2013 2:02:43 PM
Great blog. I've never heard the process so well explained with details like these. Thank you for the info and thank you to everyone involved. Fun fishing!
Coyute, CO 4/23/2013 2:03:58 PM
Excellent information. Thanks Swigs. :)
FishForAll, CO 4/23/2013 2:28:58 PM
Thanks for sharing. A tremendous effort by so many people to make this happen every year. Walleye fishing in Colorado has never been better.
Neyet Stalker, CO 4/23/2013 2:31:55 PM
The "Team" has been doing an incredible job for many years. Providing us with great opportunity on an ongoing basis. In my experience the "Marble Eye" is #1. I have had many wonderful nights stalking this supreme specie! Thanks to all of you for your continued efforts. And thanks Mr Swigle for writing/sharing some valueble insight!! Go Walleye!!!
Raptor22, CO 4/23/2013 5:17:27 PM
Thanks for the information, what is it about Colorado waters that makes them unsuitable for natural walleye spawning?
Ben Swigle (Swigs), CO 4/24/2013 6:36:03 AM
It's not just Colorado waters I always wondered why anglers were allowed to fish the dam at McConaughy. Later I learned that reproduction was essentially non-existent thus there was zero reason not to allow fishing.
There is no a single parameter but likely a combination of factors that limits natural reproduction.
1. Habitat. In their native range, walleye will travel to tributary streams to lay their eggs over clean cobble. Generally, inlet streams in Colorado are irrigation ditches. In the great lakes, walleye will spawn over wind swept shoals which contain cobble materials that are kept free of silt by the wave action. Sure, some of these habitats occur in Colorado Reservoirs but represent such a small portion of the available habitat it's not enough to make a difference.
2. Turbidity. Many of Colorado Reservoirs, especially those out east, are turbid. What can happen is a tiny piece of silt "clogs" the macropile where a single sperm would normally fertilize the egg. Thus many eggs go unfertilized. The extremely clean and clear water in Horsetooth and Carter is an advantage in this aspect. Carter has only been stocked twice with walleye, 1974 and 1976.
3. Water level fluctuation. In general, water levels in Colorado Reservoirs is low during the spring in order to catch the runoff. Lower water levels means a portion of rip-rap might be out of the water. But keep in mind, the A+ preferred spawning substrate is the smaller cobble material over a natural inlet or shoal, rip-rap is not preferable thus you see poor natural reproduction.