by the Northeastern Region Sportfish Crew, Utah Division of Wildlife Resources
Over the 13 October 2014-16 October 2014 time period, we initiated Fall Walleye Index Netting (FWIN) at Starvation Reservoir. The FWIN procedure was developed in Ontario, Canada as a way to standardize information between walleye waters. This was the first successful attempt to FWIN net at Starvation Reservoir.
Data collected was used to calculate relative abundance, length distribution and condition of all species with an emphasis on Walleye. Relative abundance of each species was characterized as catch-per-unit effort (CPUE) and as either fish caught by net night or fish caught by net hour.
A total of 342 fish were captured in 22 gill nets during the 2014 FWIN surveys at Starvation Reservoir. Species captured included Smallmouth Bass, Walleye, Rainbow Trout, Brown Trout, Yellow Perch, Common Carp, Utah Chub and Flannelmouth Sucker. Water temperature ranged from 13.8 C – 14.9 C at the time of net retrievals. Average total length of net sets was 24.13 hours (target set is 24 hours). Average CPUE for all species was 0.65 fish net/hour or 15.5 fish net/night. The highest CPUE observed by individual net was 1.6 fish net/hour or 36 fish net/night and the lowest was 0.13 fish per net/hour or 3 fish per net/night.
A total of 169 walleye were captured. CPUE for Walleye only was 0.31 fish net/hour or 7.68 fish net/night. Mean total length of these 169 Walleye was 527 mm (95% CI = 507 mm- 546 mm) with mean total weight of 1857 g (95% CI = 1664-2051 g) and mean Wr of 98.7 with a 95% CI range of 98.3-99.05. Visceral fats were collected on a scale of 0-5 with zero being no visceral fat and five being abundant visceral fat.
Average fats for this population were 2.94 with a 95% CI range of 2.69-3.19. Proportional Size Distribution
(PSD) values for Walleye at Starvation are as follows: 85 (stock to quality), 69 (quality to preferred), 46 (preferred to memorable), and 0 (memorable to trophy). Trophy size walleye are 760 mm or larger; none were captured in the 2014 FWIN.
Of 169 fish collected, 43 were identified as male, 110 were female and 16 were unknown. Level of maturity was also determined with 154 fish being mature, 4 fish immature and 16 fish unknown.
Walleye stomach content analysis was conducted during this FWIN survey and yielded 59 (35%) with stocked Rainbow Trout in the stomach. These Rainbow Trout were stocked in September of 2014 at approximately 10 in. At most, one walleye had consumed three stocked Rainbow Trout in the hours prior to being captured in the gill net. Twenty-two Walleye (13%) had consumed a variety of other fish species including Yellow [ Perch, Brown Trout, Walleye and unidentifiable fishes. Two Walleye had each consumed 6-12 young-of-year Brown Trout before being captured in the gill nets. Two smaller Walleye had consumed zooplanktons and insects. One Walleye had consumed crayfish. Thirteen Walleye (7%) stomach contents were not recorded at the time of sample processing. Seventy-two Walleye (42%) had empty stomachs.
Age structure for Walleye captured during the Starvation FWIN netting yielded interesting results. Of the 169 Walleye captured, 124 fish (73%) were effectively aged. Age distribution of Walleye capture in 2014 was comprised of fish ranging from 1 to age 13. All year classes of fish appear to be represented suggesting good recruitment from year to year. Age-5 fish represented the highest number captured within the sampled population. Several year classes had representation in this survey with age-6 to age-10 fish well represented. In this particular survey the younger fish including young-of-year to age-2 were the least represented.
A total of 75 Rainbow Trout were captured in the 2014 FWIN net surveys at Starvation. Of these 75 fish,
67 were represented in the overall statistics here. Mean total length for Rainbow Trout was 376 mm
(95% CI = 355-398 mm). Maximum total length for Rainbow Trout was 520 mm. Mean weight of Rainbow
Trout was 678 g and mean Wr was 98.6. CPUE for Rainbow Trout was 0.14 fish net/hr or 3.4 fish per net/night.
A total of 15 Brown Trout were captured in the 2014 FWIN survey. Mean total length was 468 mm and
mean weight was 1106 g. Wr of these Brown Trout was 95 with a range of 90-99. CPUE was 0.028 fish
per net/hour or 0.68 fish per net/night. One notable fish was a 725 mm, 4794 g fish captured in the
north end of the reservoir. This fish was a mature male and was eating stocked Rainbow Trout at the
time of capture.
A total of 56 Smallmouth Bass were captured in 2014 FWIN surveys. Mean total length for these fish was 348 mm and mean total weight was 665 g. Wr for Smallmouth Bass was 99.3 with a range of 96- 101. CPUE for Smallmouth Bass was 0.10 fish per net/hour or 2.54 fish per net/night. During this FWIN survey we also collected stomach content and age data for Smallmouth Bass. Smallmouth Bass collected ranged from 1 to 8 years of age with 47 (84%) of these fish being classified as female and 15 (26%) classified as male. Smallmouth Bass in Starvation forage mostly on crayfish but do consume other fishes within the reservoir as the opportunity exists.
Yellow Perch Nettings
To better understand the prey base in Starvation Reservoir, we set four perch-specific nets in August, not associated with annual trend or FWIN netting. A total of 148 Yellow Perch were captured in these four gillnets resulting in a CPUE for Yellow Perch of 1.85 fish per hour or 37 fish per net/night. Average total length for Yellow Perch was 114 mm and average weight was 19 g. Wr was 100 with a range of 84- 131. Perch were found in each of the four nets from the Strawberry River arm to the points across from Juniper Springs. Perch were most abundant in the shallows and where submerged vegetation exists.
We sampled Walleye in 2014 that ranged from 244 mm to 745 mm in total length. The largest Walleye
observed in our nettings in 2014 was 527 mm. Walleye also had good mean Wr of 98.7 and were overall
in good condition, which indicates they are able to find sufficient forage. At this time, the Walleye population at Starvation Reservoir is comprised of larger fish as indicated by a high PSD (89) with most fish falling between 475 mm-700 mm range. During this survey, smaller Walleye were least abundant with no
young-of-year fish captured and few age one fish. Many of the fish captured in 2014 were large and mature
female fish which could indicate a strong spring spawn in 2015, though recruitment from this remains
to be seen.
Other species of fish in Starvation Reservoir are doing well with relative weights in the upper 90s. Relative
abundance of these species does differ greatly according to the 2014 FWIN, but all continue to show
up in creel surveys and angler reports. Rainbow Trout are stocked annually at a rate of 50,000 (10 in)
fish and are normally stocked in the fall months of September or October. The addition of Rainbow Trout
to the reservoir likely changed the food web therein; however, we have very little pre- stocking information
with which to compare the current condition. Foraging trends by all species appears to change with the
seasons and has produced some interesting results.
All fishes in the system utilize zooplanktons during early life stages and one of the main reasons Rainbow
Trout were initially stocked into the reservoir was because of the abundance of zooplanktons at the time.
During the winter and spring months at Starvation, both Walleye and Rainbow Trout utilize Yellow Perch
and this appears to be lakewide. We have documented both species with Perch in the stomach in both
seasons. One of the most interesting observations as a result of the 2014 FWIN surveys was the fall utilization of stocked Rainbow Trout by large mature Walleye.
In several published papers (Baldwin et al. 2003, Yule et al. 2000) stocking of a 10 in fish to avoid predation
by Walleye appeared to be successful. In Starvation this appears to be the case until Walleye reach a certain size, then these 10 in stocked Rainbow can easily become just another forage fish. Our suspicions are that 2014 is not the first year in which large adult Walleye have heavily predated on stocked Rainbow Trout. The overall condition of the fish that were consuming these Rainbows was amazing with visceral fats between 4-5 on most fish. It is possible that stocking of Rainbow Trout each fall has a significant effect on the ability of anglers to catch large Walleye in the fall months.
Another notable observation is the distribution of Walleye and large Walleye in the Reservoir. The north
end of the lake held 58% of all Walleye captured and mostly female individuals. The majority of smaller
Walleye and a large percentage of male Walleye were captured in the middle and south ends of the reservoir.
All species utilize Perch in this system; large and mature Walleye utilize stocked Rainbow Trout; Smallmouth Bass heavily utilize crayfish and everything utilizes the rich and abundant zooplanktons that exist in Starvation Reservoir during some life stage. The lack of the Utah Chub over several years seems to indicate it is not an important or utilized part the food web in Starvation now.
It appears that in 2014 Starvation is a dynamic, big-fish producing reservoir with species of all types finding and settling into their niches. This fishery is becoming very popular for Rainbow Trout with the completion of the 2014/15 creel census in March of 2015 we will know more about its use and its harvest of all species.
Thanks to all who helped with the 2014 Starvation surveys!