Bits & Pieces: Walleye Harvest, Bass Tagging, & Knot Selection

Fishery Science: Effects of High Walleye Harvest

Angler harvest of walleyes has—although maybe based more on intuition than good science—always been a concern as evidenced by decades of length and possession limits. More anglers equipped with more knowledge, better tackle, and advanced marine electronics and declines of some walleye fisheries have increased concern about the effects of exploitation on walleye populations. A recent study by Wisconsin Department of Natural Resources and Great Lakes Indian Fish and Wildlife Commission fishery scientists adds new information to the walleye management playbook.*

Through a combination of liberalized angler harvest regulations, tribal spearfishing, and, as necessary, physical removal, 50 percent of the adult walleye population was harvested for 10 successive years from Sherman Lake, a 123-acre natural lake with a naturally reproducing walleye population. The 50 percent exploitation rate was far higher than the average of 17 percent exploitation measured in other lakes in the area subjected to recreational harvest or recreational harvest plus tribal spearfishing. Changes in important population variables were compared between the 10 years of 50 percent exploitation (treatment period) and the 10 preceding years (pre-treatment period) when walleyes were harvested by recreational anglers and tribal members but at a lower annual rate. Changes in the walleye population were also compared to the same variables measured in nearby Escanaba Lake, a 293-acre lake with essentially no walleye harvest. This comparison allowed for variations in the population variables that may be attributable to climatic variations, like temperature cycles and water levels, and other unmeasured forces.

Adult walleye density remained similar between high-exploitation years and the preceding 10 years, but population size structure (the proportion of larger fish) declined. Walleyes reached sexual maturity earlier and at smaller lengths (about 1 inch for males and 3 inches for females) during the high-exploitation period. The abundance of young-of-the-year walleyes measured in the fall did not differ between treatment and pre-treatment periods, but the abundance of age-1 walleyes was greater during the treatment period; survival from age 0 to age 1 increased during higher exploitation. Length at age 1 increased significantly from 6.8 inches pre-high exploitation to 8.5 inches during the high-exploitation period. Lengths at ages did not differ between pre-treatment and treatment periods for adult walleyes, except 6- and 7-year-old female walleyes were 1 to 2 inches larger during the high-exploitation period. Meanwhile, few changes occurred in the unexploited Escanaba walleye population, suggesting the changes in Sherman were due to the exploitation treatment rather than any environmental conditions.

A concern about high exploitation is reducing the number of sexually mature spawners to the point where recruitment declines. The highly exploited Sherman Lake walleye population responded by earlier maturity to sustain recruitment. The lack of difference in length-at-age of adult walleyes (except for the oldest females) suggests that the energy available per surviving adult may have been channeled into eggs and sperm rather than body growth. If so, this would be a population adaptation to ensure continued recruitment.

But this response of channeling available energy to ensure reproductive products is not universal. In a similar Wisconsin DNR study in 665-acre Big Crooked Lake, increasing exploitation to 35 percent by intentional removal of adult walleyes significantly reduced adult walleye abundance and population size structure but increased the growth rate of adults; the effect on length at maturity was not measured.**

Reasons for different population responses between Sherman and Big Crooked lakes are not apparent. Big Crooked Lake was larger and had a more diverse forage base. And exploitation in Big Crooked Lake, although high, was less that the 50 percent exploitation in Sherman Lake. These studies, as well as several others, identify ways that walleye populations may be resilient to high exploitation; but they also point out that high exploitation can reduce walleye abundance and size structure, two population characteristics important to anglers.

–Dr. Hal Schramm

*Sass, G. G., S. L. Shaw, L. W. Sikora, M. Lorenzoni, and M. Luehring. 2021. Plasticity in abundance and demographic responses of walleye to elevated exploitation in a north temperate lake. N. Am. J. Fish. Mgmt. 42:535-548.

**Sass, G. G., and S. L. Shaw. 2018. Walleye population responses to experimental exploitation in a northern Wisconsin lake. Trans. Am. Fish. Soc.147:869-878.

Genetic Breakthrough: New Bass Tagging Technique

Stocking is one of the widespread and traditional forms of fishery management. In the case of black bass, it’s been done in newly built fisheries, for supplementing poor year-classes, and to offset losses due to overharvest or environmental damage.

Early on, managers stocked fingerling fish and hoped for the best. Clipping of fins and chemical marks such as oxytetracycline have been used with mixed success. More recently, coded wire tags (CWT) have been widely used to evaluate the success of stocking by collecting a large sample of fish at a later time, checking for tags, and estimating the contribution of stocked fish to the population. The tiny wires are inserted into the fingerlings prior to release. When captured, a wand passed over the fish identifies that individual.

A more efficient, economical, and benign method called Parentage-Based Tagging (PBT) relies on recent genetic breakthroughs. It was initially developed for use in salmonid hatcheries to evaluate the contributions of fish stocked to support poorly reproducing populations or to enhance endangered species, where it’s proved useful. Recently, a team of biologists from the North Carolina Wildlife Resources Commission (NCWRC) and the University of Florida used PBT to evaluate supplemental bass stocking at Lake Mattamuskeet, a large lake in North Carolina where low recruitment has been a problem.*

From 2014 to 2017, they collected genetic data using fin clips to extract the DNA of 184 wild adult bass from four locations, yielding a PBT genetic baseline that could be used to identify parentage of their offspring. Broodstock were released into several ponds to spawn naturally. Over three years, over 140,000 fingerlings were produced and released into several suitable locations around Lake Mattamuskeet. Collecting sufficient samples later via electrofishing, biologists checked the DNA and determined which bass had parents spawned in the hatchery and which ones were wild.

The team found that the genetic baseline was effective for identifying individual fish and discriminating among closely related individuals, such as siblings. Error rates were very low, with no false positives. Results showed that the contribution of stocked bass was rather low, ranging from 2 to 8 percent, and it varied by year. Due to the minor contribution of stocked bass to year-classes and high costs, NCWRC stopped the stocking program. Instead, the agency devoted efforts improving habitat for spawning and rearing of juveniles. The bottom line is that PBT was a cost-effective and highly accurate method of calculating the success of stocking programs at supplementing wild populations.

*Hargrove, J. S., K. J. Dockendorf, K. M. Potoka, C. A. Smith, V. Alvarez, and J. D Austin. 2022. Largemouth bass hatchery contributions quantified via Parentage-Based Tagging. N. Am. J. Fish. Mgmt. 42:758-774.

–Steve Quinn

From the Archives: Hook Attachment Details

History is full of examples where innovations have been developed in complete isolation from one another. Invariably, ideas lost with one civilization spring up again, perhaps separated by centuries, and with no apparent influence on one another. In fishing, too, good ideas get forgotten and rise again or evolve from seemingly disparate sources. Such is the case when examining the parallels between the hook and knot selection of many top bass pros and the collective trend among serious carp anglers.

Bass pro Denny Brauer says he prefers a straight-shank worm hook over an offset. He reasons that a softbait slides down a straight shank more easily, focusing more energy on hook penetration.

Other bass anglers take things further by tying the line directly to the hook shank with a snell knot. It’s important with this rigging that the line be fed up through the eye, which imparts a cam-action to the hook, pushing the hook point forward under pressure. Carp anglers refer to this configuration as the “trap” and often accentuate it further by adding a short length of shrink tubing. By rigging the bait on a trailing line loop, the hook point remains fully exposed for optimal hooking.

Kevin VanDam also points out that tying to the hook shank prevents the knot from being damaged by worm weights. Braided lines are particularly susceptible, he says, especially when fished with brass or tungsten weights.

–Lonnie King

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