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Bits & Pieces: Quick Hits Regarding Shrinking Walleyes, Colorado Trout, and A-rig Storage

Blending fishery science with everyday fishing.

Bits & Pieces: Quick Hits Regarding Shrinking Walleyes, Colorado Trout, and A-rig Storage

A recent study found that walleyes typically shrink after capture, with the extent of shrinkage dependent on water temperature, holding method, and freezing.

This article originally appeared in the Oct-Nov 2021 issue of In-Fisherman.


Shrinking ‘Eyes?

Curious Connections—After an angler, cited by a conservation officer for possessing walleyes under the minimum length limit, contested the violation by claiming his fish had shrunk, biologists with the South Dakota Department of Game, Fish, and Parks (where the case had occurred) investigated this possibility, for shrinkage of walleyes caught in open water and ice-fishing.*

Walleyes caught in open water were either placed in a cooler with ice or into a livewell. Ice-caught fish were placed in a cooler with ice. Biologists measured the fish at capture and every hour for the next 10 hours. Some fish also were checked after 20, 29, 36, and 44 hours. Finally, the biologists froze the fish and then checked them 30 days later. In poaching cases, fish often are held frozen for at least 30 days as evidence.

The study found that walleyes do typically shrink after capture, with the extent of shrinkage dependent on water temperature, holding method, and freezing. Fish caught in open water and placed on ice averaged just 1/10 inch shorter after 5 hours, but some shrank by up to 1/3 inch, slightly more after an additional 5 hours. Walleyes caught in cooler water (50°F) shrank more than those in warmer conditions.

Shrinkage was attributed to rigor mortis. Walleyes caught and placed in a livewell died quickly and generally increased in length, though the change was not statistically significant. Expansion was apparently due to a process called “gaping” that takes place after rigor mortis has passed and the flesh is less able to contract due to tissue damage, resulting in increased length.

Walleyes caught ice fishing and placed on ice in a cooler took longer to shrink as they remained alive longer, but 24 hours later showed similar amounts of shrinkage, averaging about 1/5 inch.

Greatest shrinkage occurred when walleyes were frozen, with some fish shrinking almost 1/2 inch. This amount of shrinkage presents a problem for enforcement of length limits when frozen fish are used as evidence. As a result, the biologists recommended that officers photograph confiscated fish on a measuring board and use the photos as evidence instead of frozen carcasses. They also noted that ice anglers often place their catch on the ice where fish quickly freeze. This likely causes significant shrinkage as well, though it was not measured in this study.

-Steve Quinn

*Blackwell, B. G., M. J. Hubers, and R. G. Losco. 2003. Postharvest length changes of angler-caught walleye. N. Am. J. Fish. Mgmt. 23:770-778.




Reservoir Stocking Program

Management in Action—Whirling disease was first detected in major waterways in Colorado in 1987, with noticeable effects by 1988, and by 1994, 95 percent of the rainbow trout population in some areas, including the South Platte drainage, had vanished. With the help of the Colorado Department of Wildlife and Parks, Spinney Mountain Reservoir trout then overcame three additional challenges in the past 20 years: growth rate, pike, and perch.  

A man holding a large rainbow trout for the camera on a reservoir in Colorado.
Hofer-strain rainbow trout have developed an immunity to the effects of whirling disease.

To combat whirling disease, Hofer-strain rainbow trout were chosen to anchor the genetic pool. Originally raised at a hatchery in Bavaria, Germany, for over a century, these rainbows had developed an immunity to the crippling spores. The weakness with Hofer-strain rainbows is that they are a tame fish with few predatory and self-preservation instincts.

Harrison Lake sits 30 miles outside of Bozeman, Montana, and had one of the first whirling disease-resistant strains or rainbows to be found in the states. These DeSmet strain fish were originally transplanted from California to Wyoming in the 1800s, then to Montana, and had somehow developed an immunity before the disease arrived on the continent. By 2002 the Colorado Department of Wildlife and Parks brought Harrison Lake rainbows to the state, and the researchers eventually bred Hofer-Harrison strains.

Recommended


Tyler Swarr, aquatic biologist for the Upper South Platte River basin, explains, “Over time we hope that the wild South Platte rainbows will build resistance to the disease by introducing some of these resistant genetics. This has been done with success in the Gunnison River, and we’re starting to see modest wild recruitment in a couple of locations along the Upper South Platte.”  

A third genetic crossing adds Snake River cutthroat trout from Wyoming. Unlike other cutthroat species, Snake River strains grow well in hatcheries and even better in food-rich reservoirs like Spinney. This keeps the fish high on anglers’ lists for size as well as solving another problem: predation from pike. “By 2001, we implemented a statewide unlimited bag on pike while also stocking larger 10-inch catchable rainbows at Spinney to reduce immediate predation. In 2010, we began stocking Spinney and Elevenmile reservoirs through the ice in December through March when the metabolism of pike is lowest, further reducing losses,” Swarr says. With an extra 2-inch head start, the trout thrive with abundant populations of freshwater scuds, callibaetis, and chironomids, along with abundant weedy habitat for cover, and no winter ice fishing, to reduce overall angling pressure.       

This delicate puzzle was potentially upset by the arrival of perch into the system. While the perch population is not yet large enough to attract anglers, it did successfully divert some of the focus from pike, creating strong year-classes of trout. The decades of work and a little bit of luck finally produced an ecosystem with balanced populations of state-record pike along with abundant and trophy-size trout while avoiding disaster from whirling disease population crashes.

-David Harrison

A-Rig Storage

Tackle Tip—Mark Davis, longtime In-Fisherman friend and host of BigWater Adventures television show, sent us his solutions for A-rig storage.

An a-rig.
Mark Davis sent us his solutions for A-rig storage.

 On the rod, hook one jighead to the hook keeper on the rod, then use a rubber band to corral the remaining hooks, therefore neutralizing the annoying tangles and danger inherent to unruly A-rigs.

An A-rig in a boat storage compartment
Several loose rigs can be neatly organized and stowed in a bucket.

Several loose rigs can be neatly organized and stowed in a bucket, with a hanger fashioned out of wire and wrapped with tape. Hang the rigs from the wire, with jigheads/hooks safely tucked away in the bucket. Stow the bucket out of the way in a boat compartment.

An A-rig in a bucket.
Hang the rigs from the wire, with jigheads/hooks safely tucked away in the bucket.

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