05-14-2012, 11:23 PM
one8sevenn,
It looks like TubeDude and kokeking answered many of your questions and addressed most of your concerns. I thought I would also just clarify a few myself, but I really appreciate those guys sharing their knowledge.
There are two strains of kokanee in the Gorge. The Kootenai strain is an early run and more prone to spawning in inflows, peaking around the middle of September. The other strain, which we term the Roaring Judy strain, is a late run and more prone to spawning in-reservoir from October-November. Previous research conducted by USU has shown the late run strain (in-reservoir spawner) is the source of most of the kokanee recruitment, ~95%. The other ~5% is from tributaries, including the Green River and Sheep Creek. Being the kokanee population in the Gorge is so dependent on the in-reservoir spawning group, the impacts of burbot on kokanee recruitment is more of a concern. We have documented kokanee eggs in burbot diets during routine and exploratory sampling in the fall, but many anglers have also witnessed the same thing. The same goes for lake trout eggs, which are commonly observed by anglers in burbot stomachs in the fall.
Unfortunately, this seasonal dietary usage hasn't not been quantified or even published in a report to date. There was a USU study completed on burbot from 2008-10 (report available) but eggs, and kokanee overall, were not a big component of the burbot diet. Crayfish were obviously the dominant food item, at 90%. It was a study directed on overall trends of burbot in the reservoir, but not directed solely on impacts to kokanee. Unfortunately, some of the sites and possibly the timing of the sampling events did not overlap well with the kokanee cycle.
There has been a lot learned from the Burbot Bash tournament, including population estimates, diet trends, movement, etc. Burbot are checked by biologists and many of the burbot stomachs are examined either at the check station or back in the lab. Kokanee are not the dominant food item, but are a more common occurence during the winter, especially in larger burbot (>30 inches). I suspect the winter time period offers more habitat overlap, where kokanee will spend more time shallow or near shore at the ice edge, consuming abundant zooplankton, and burbot are not limited by thermal tolerances.
I also don't think burbot are "destroying the kokanee fishery", but I don't believe they are helping it either. There's only so much food to go around. Kokanee are loved by many predators, including burbot, lake trout, and even anglers. Kokanee abundance can also be limited by reservoir elevation changes, water quality, disease, etc. As you well know, fish populations are very dynamic and just one variable is rarely to blame.
Finally, in regards to the Vernal Express article, those were comments (among a few others) that were inaccurate. They weren't those of a biologist, but instead those of a reporter misunderstanding a biologist. I don't fault the guy too much, being he was standing on the ice in Nike tennis shoes, in the dark, when it was 20F, with a 15-20 mph wind.
I hope this helps some, Ryno
[signature]
It looks like TubeDude and kokeking answered many of your questions and addressed most of your concerns. I thought I would also just clarify a few myself, but I really appreciate those guys sharing their knowledge.
There are two strains of kokanee in the Gorge. The Kootenai strain is an early run and more prone to spawning in inflows, peaking around the middle of September. The other strain, which we term the Roaring Judy strain, is a late run and more prone to spawning in-reservoir from October-November. Previous research conducted by USU has shown the late run strain (in-reservoir spawner) is the source of most of the kokanee recruitment, ~95%. The other ~5% is from tributaries, including the Green River and Sheep Creek. Being the kokanee population in the Gorge is so dependent on the in-reservoir spawning group, the impacts of burbot on kokanee recruitment is more of a concern. We have documented kokanee eggs in burbot diets during routine and exploratory sampling in the fall, but many anglers have also witnessed the same thing. The same goes for lake trout eggs, which are commonly observed by anglers in burbot stomachs in the fall.
Unfortunately, this seasonal dietary usage hasn't not been quantified or even published in a report to date. There was a USU study completed on burbot from 2008-10 (report available) but eggs, and kokanee overall, were not a big component of the burbot diet. Crayfish were obviously the dominant food item, at 90%. It was a study directed on overall trends of burbot in the reservoir, but not directed solely on impacts to kokanee. Unfortunately, some of the sites and possibly the timing of the sampling events did not overlap well with the kokanee cycle.
There has been a lot learned from the Burbot Bash tournament, including population estimates, diet trends, movement, etc. Burbot are checked by biologists and many of the burbot stomachs are examined either at the check station or back in the lab. Kokanee are not the dominant food item, but are a more common occurence during the winter, especially in larger burbot (>30 inches). I suspect the winter time period offers more habitat overlap, where kokanee will spend more time shallow or near shore at the ice edge, consuming abundant zooplankton, and burbot are not limited by thermal tolerances.
I also don't think burbot are "destroying the kokanee fishery", but I don't believe they are helping it either. There's only so much food to go around. Kokanee are loved by many predators, including burbot, lake trout, and even anglers. Kokanee abundance can also be limited by reservoir elevation changes, water quality, disease, etc. As you well know, fish populations are very dynamic and just one variable is rarely to blame.
Finally, in regards to the Vernal Express article, those were comments (among a few others) that were inaccurate. They weren't those of a biologist, but instead those of a reporter misunderstanding a biologist. I don't fault the guy too much, being he was standing on the ice in Nike tennis shoes, in the dark, when it was 20F, with a 15-20 mph wind.
I hope this helps some, Ryno
[signature]