Blue Mesa Fisheries Update - Colorado Parks and Wildlife · Dan Brauch and Adam Hansen Colorado Parks and Wildlife December 18-19, 2019. Blue Mesa Fish Update. ... Do this at night,

Blue Mesa Fisheries Update

Dan Brauch and Adam HansenColorado Parks and Wildlife

December 18-19, 2019

Blue Mesa Fish UpdateBMR fisheryKokanee managementLake trout managementLake trout harvest incentive

Blue Mesa Fishery Goals

Goal #1: Provide Blue Mesa anglers with best fishing opportunities for kokanee, rainbow trout, trophy lake trout and brown trout.

Goal #2: Maintain Blue Mesa as source of kokanee eggs to provide kokanee fishing opportunities at 28 lakes in Colorado.

Blue Mesa Reservoir Fisheries

Supports up to 450,000 hours of angling annually.“Destination” Fishery—Up to 2/3 of anglers are from Colorado’s East Slope or from out of stateGross economic estimated to be $12.3 million in today’s dollars ($5.43 million in 1987).Curecanti NRA was responsible for an estimated $44 million in economic value in 2014.

Kokanee & lake trout are not co-evolvedLake trout stocked in Colorado in late 1800’s, Kokanee in 1951

Kokanee and Lake Trout

Blue Mesa Kokanee• Stocked after Blue Mesa Dam completed (1965)

with Granby source (Flathead L, MT 1951-1957)• Currently states primary egg source—natural

reproduction is minimal in Colorado

02468

1012141618

Egg

Tota

l in

Mill

ions

Year

Kokanee Spawntake Totals by Water 2000-2019

Antero

Blue Mesa

Cheesman

Eleven Mile

Granby /Shadow Mt.

McPhee

Lake Nighthorse

Vallecito

Williams Fork

Wolford

Kokanee Fishing

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Kokanee percent of total catch

Year

Kokanee Contribution to Blue Mesa Catch May through October

Presenter

Presentation Notes

Average 65% of catch during the May through October time period, supporting up to 450 thousand angler hours of use, and contributing about $8 million worth of input to the local and state economy.

Kokanee Grow Trophy Trout

Presenter

Presentation Notes

Kokanee have the highest energy density among coldwater prey species allowing extreme growth of lake trout.

0%

20%

40%

60%

80%

100%

age 3 age 4-6 age 7-25

InvertebratesCrayfishPerchRainbow TroutKokanee

Stable Isotope proportion of MAC diet 2010 (CSU)

MAC Age

Die

t Pro

porti

on

(12-16”) (17-23”) (24-44”)

Presenter

Presentation Notes

Carbon isotope ratios indicate what diet consists of while change in nitrogen ratios indicate a higher tropic level. Previous diet study showed about 50/50 rainbow trout and kokanee before rainbow trout stocking were shifted to a 10 inch stocked fish.

Sonar transects

2009

2002

Presenter

Presentation Notes

Run transects across the reservoir with an echo-sounder. Do this at night, dark of the moon, because typically that’s when the fish are the most distributed and so more detectable. You get a collection of return echoes that the fish tracking algorithms decide are fish, and each fish has a Target Strength associated with it, which is the amount of sound in dB bounced back from the fish. The bigger the target strength the bigger the fish. Of course as your beam moves through the water you’ve got a bigger chance of seeing a fish down deep than up in the narrow part of the beam, so you can’t just count up the number of fish you saw and extrapolate, you’ve got to weight each fish according to volume sampled and so on, but that’s all manageable. Periodically, we set experimental gill nets overnight in each of the three basins, concurrent with the survey. Vertical gill nets having a total of 6 different mesh sizes and extending from the surface to within a few meters of the bottom to get a good ground-truthing representation of the pelagic region that is sampled by hydroacoustics. Most fish sampled are kokanee.

Sonar Estimates 1994-2019

Lake Trout Management / Regulations

• Late 1980’s 1 fish over 20 inches (86-87)• 1990-1995 22-34 inch fish must be returned

(slot)• 1996-2010 8 fish bag limit• 2009- 2011 CPW netting to reduce predation

AND reduce reproductive capacity• 2011- 1 fish over 38 inches, unlimited under 38• 2012-2017 CPW netting to reduce predation

(reduced length target: 32” to 30” to 28”)• 2016- 1 fish over 32 inches, unlimited under 32

Presenter

Presentation Notes

Sporadic stocking occurred (1968-1992) Natural reproduction documented early 1990’s followed by population expansion (denoted by red line)

Lake Trout Abundance

Presenter

Presentation Notes

It appears that angler harvest and CPW netting has resulted in a halt to lake trout population growth, although reduced recruitment during 2012-2013 could have been a factor. Continued harvest is needed to insure population growth remains in check.

Predatory Lake Trout Abundance

• Goal 1: Manage predation on kokanee to maintain kokanee fishing, eggtake and prey availability for trophy lake trout

• Goal 2: Provide quality opportunities for trophy lake trout

Lake Trout Management 2020

2 Tools: Angler harvest and CPW netting

0

50

100

150

200

250

300

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Angler Returned 09-12 Angler Harvested 09-12

Angler Catch 2009-2012

0

500

1000

1500

2000

2500

3000

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Netting Removal Incidental Mortality Netting Released

Netting Catch 2009-2019Incidental mortality a concern

Lake Trout Harvest 1996-2018

Netting Catch 2009-2019Not popularIncidental mortality a concern

Presenter

Presentation Notes

Angler harvest most important (7,000 vs ~1,200), but supplemental netting (about 4-6% bump in harvest) appeared to be enough to curtail lake trout population growth Is it possible to increase angler harvest to replace supplemental netting harvest through a harvest incentive program?

Kokanee VS Lake Trout Abundance

• Only incentivize harvest up to 24 inches:• Consume the most kokanee• 96 percent of lake trout removed by CPW AND of

lake trout kept by anglers are 24 inches and smaller.

• 83 percent of released lake trout under 24 inches• Harvest about 30%, far below unsustainable levels,

so significantly more harvest can occur (>50%-55% continued harvest would likely be unsustainable)

• Population monitoring and modelling will guide program (creel, sonar, SPIN lake trout study) to insure moving towards goals.

Lake Trout Harvest Incentive Proposal

Presenter

Presentation Notes

Percentages since 2009

• Only heads accepted from fish under 24 inches• Dropped off at CPW offices (Gunnison and

Montrose) and Blue Mesa?• Propose 2020 contest February through July• Prizes for:

• Most lake trout turned in ($1000, $500, $250??)• Turned in coded wire tagged fish (propose $250

per tagged fish)• Randomly selected (one chance per head turned

in) 20 $200 prizes• Other donated prizes?

Lake Trout Harvest Incentive Proposal

• Continue stocking 3.5 million kokanee annually

Blue Mesa Recommendations

• Maintain kokanee survival by managing lake trout population/predation through angler harvest; achievable at Blue Mesa?

• Resume netting if angling harvest is shown to not control population growth; minimize netting


• Assess lake trout management annually and provide recommendations for changes

• Maintain kokanee, brown trout, rainbow trout and trophy lake trout angling opportunities

• Monitor gill lice to assess effect on kokanee fishery


Documents

Blue Mesa Fisheries Update - Colorado Parks and Wildlife · Dan Brauch and Adam Hansen Colorado Parks and Wildlife December 18-19, 2019. Blue Mesa Fish Update. ... Do this at night,