by Michael Carey, July 04, 2017
Perhaps you’ve heard the news that WDFW have planted triploid kokanee in Lake Roosevelt. Anglers that have are probably dreaming of monster triploid kokanee, similar to what they have seen for the triploid rainbow trout program. The fact vs. fiction however is much more interesting. When I recently confirmed with WDFW that triploid kokanee were also planted in Lake Cavanaugh I knew I wanted to find out the rest of the story. Justin, a Fish Biologist at WDFW was very generous with his time as he explained the history of triploid kokanee and how the program is progressing in Washington.
First off, let’s learn just what a triploid kokanee is and how they are created. Triploid kokanee, like triploid trout, are produced at the egg stage of the fish production. The Kokanee eggs are harvested from returning adults, shocked to produce the triploid mutation, and reared to the eyed egg stage at Lake Whatcom Hatchery. They are then shipped to other facilities to grow and stock: Arlington Hatchery for Lake Cavanaugh and the Spokane Tribal Hatchery for Lake Roosevelt.
Idaho and British Columbia were the first to experiment with making a triploid kokanee. Fisheries biologists there have been working to determine the benefits and disadvantages of managing Kokanee fisheries with triploid fish. Pre Justin, British Columbia has found that in small lake fisheries most male triploid still mature and die by three years old, but females do not and continue to live for about five years. Idaho has also observed longer lived fish, but results for survival and growth, which appear to be lower for triploid fish until adulthood at age 3, have been obscured by competition between triploid and diploid fish in the same lakes. Little difference has been observed between maximum sizes of diploid and triploid fish, which isn’t surprising since Kokanee are highly density dependent and growth is directly related to the number of mouths, are feeding on a finite food supply. Idaho is currently working on a before-and-after study in multiple lakes to better evaluate physical and fishery performance of switching to triploid fish, but we haven’t seen the results from that work, yet.
I asked Justin what were the advantages and goals of producing triploid kokanee? He stated that “The primary advantages to triploid Kokanee are longevity and reduced risk of genetic integration with wild stocks. Longer lived fish are more likely to recruit to the fishery and increase harvest of stocked fish, which is why we stock them in the first place. Stocking sterile fish that are marked allows managers to offer mark-selective recreational opportunity while protecting both the genetic integrity and survival of wild fish.”
“The intended outcomes of this program are that the longer lived fish will be more likely to be caught by anglers before they die naturally, recruit to the fishery in the winter, and possibly grow larger than diploids. It is still unclear if enough fish will survive to noticeably affect the Cavanaugh fishery, but we do know that some did because two ad-clipped Kokanee (13 inches long) were observed in July 2016.”
“We are still in the early phases of building our understanding of these characteristics. To date, our efforts in Cavanaugh have focused on consistently producing the fish. I haven’t spoken with eastern Washington bios about Lake Roosevelt, yet. The next phase in Cavanaugh is to evaluate the triploid Kokanee population and we are still developing those strategies.”
WDFW began producing triploid Kokanee in 2014 and first stocked them in Cavanaugh in September 2015. All Kokanee fry stocked in 2015 and 2016 were triploid fish and numbered 24,000 and 29,000. Stocking occurs in September when fry are about 3 inches long and their adipose fins are then clipped.
My own fishing experience on Cavanaugh was in the fall of 2016.My wife and I encountered some beautiful 14-16” kokanee. After talking with Justin and looking back at pictures and I noted those fish all had intact adipose fins. If you do catch a triploid kokanee out of Cavanaugh or Roosevelt the fin will be clipped. Justin told me WDFW is hoping anglers will help them better understand the results of the program.
“We are still in the trial-and-error development phase the program. Evaluation of success is passive at that moment as we rely primarily on angler reports of fishing success. As you probably know, we have little staff time available to directly monitor the fishery, though we are able to free up a staff person on occasion to check things out as in July 2016 when we utilize the gap between peak periods for surveying streams for Salmon. I hope to improve our monitoring program as the fishery develops, but the likelihood of additional funds in the near future is low. Any help you or others can provide in encouraging the angling community to report their successes and failures in lake fishing greatly help us in our mission to provide successful fisheries to the public.”
The Lake Cavanagh Kokanee fishery is currently sustained by both natural reproduction and stocking. Prior to 2012, the fishery was sustained primarily by natural reproduction. Angler reports indicate kokanee were present in the 1970s. Kokanee were stocked once in 2004. A regular stocking program for Kokanee was established in 2012 to increase the abundance of Kokanee in the lake to meet expected increased angler demand and provide consistency to the fishery.
Here’s a couple more “fun facts” about triploid kokanee.
Do triploids change into spawning colors? After all, they are sterile fish. Justin told me “Males do according to the work from B.C., but females do not.”
Is there a cost difference to make triploid kokanee? “The additional cost is minimal and involves some additional staff time to shock the eggs and remove dead ones from rearing trays because mortality is considerably higher. Once they reach the eyed egg stage, they are reared the same (feed, flow rates, water temperatures, etc.) as other Kokanee fry.
Is there any downside to producing and planting triploid kokanee that WDFW is aware of? “We are still in the process of identifying disadvantages to a triploid Kokanee program. Triploids have a lower rate of survival (and possibly growth) to adulthood (age 3), males have been known to live a normal lifespan and doesn’t benefit the fishery from a longevity perspective, and rearing space at our facilities is limited which limits our ability to add new programs”.
As Justin previously noted, British Columbia has found that in small lake fisheries most male triploid still mature and die by three years old, but females do not and continue to live for about five years. That would infer an additional two years of growth for female kokanee that would translate into the potential for large kokanee.
What are long term plans of WDFW for triploid kokanee stocking? “We are still in the trial-and-error phase. Contribution fish to the fishery, survival, growth rate, longevity, the presence of wild stocks, and hatchery capacity will all be used to guide future decisions about the program.”
How can anglers help WDFW with this program? “Anglers are integral to inland fisheries management. To date, our efforts at Cavanaugh have been to establish consistent hatchery production and we are currently developing strategies for evaluating the efficacy of producing and stocking triploid Kokanee at a larger scale. Anglers can help us evaluate the program by recording and reporting their observations and activities (number of fish by species, number of adipose clipped Kokanee, lengths of caught fish, time actively fishing, etc.). “
Did I just hear an invitation for anglers to go fishing? I think I can get on board with that program! I hope to see some reports on Northwest Fishing Reports this year with triploid kokanee pictures in them. Let us know how you do!