Bits & Pieces: Muskie Feeding Mechanics, Bass Hyperstability, and Catfish Populations

Select Science: Muskie Feeding Mechanisms

In a laboratory setting, researchers examined when and to what extent muskies use their sight and lateral-line senses during feeding.* Different muskie groups were tested, including those with eyes and lateral lines that functioned normally, and others that had their sight, lateral line, or both senses suppressed.

When presented with a minnow, normal muskies began feeding in distinct phases. First, a muskie oriented toward the prey and then slowly stalked it. Once in position, they concluded with a fast and furious lunge. Normal muskies had successful prey captures 73 percent of the time.

Muskies with suppressed eyesight didn’t orient to or stalk prey and lunged only if an unsuspecting minnow trespassed too closely. Muskies with suppressed lateral lines stalked prey longer, closing a narrow gap before striking. Muskies that lacked both senses didn’t feed. These findings indicate that muskies rely more on sight during the first phase of feeding (the stalk), and more on the lateral-line system during the final phase (the lunge).

The see-stalk-strike behavior may explain why the figure-8 technique can be effective. During the retrieve, a muskie might be using vision to stalk a lure to the boat, but not commit to eating it. In this case, performing a figure-8 may provide the commotion and vibrations necessary to induce the lunge feeding stage via the lateral line. This research shows that lure appearance and action both can be critical in triggering muskies to track a lure and eventually strike it.

–Dr. Rob Neumann

*New, J. G., et al. 2001. Strike feeding behavior in the muskellunge, Esox masquinongy: contributions of the lateral line and visual sensory systems. J. Exp. Biol. 204:1207-1221.

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Fishery Health: Fishing’s Good, Then It’s Gone

Do angler catch rates go down when fish abundance goes down? If so, fisheries should be somewhat self-regulating because low catch rates in one place might encourage anglers to fish elsewhere, allowing the population to recover. In some cases, however, catch rates can remain high even as fish abundance declines. This phenomenon, known as “hyperstability,” has contributed to unforeseen collapses of recreational and commercial fisheries. When hyperstability is at play, catch rates vary between days and anglers, but a decline will not be evident until the population has already been overfished.

In a recent study, researchers conducted the first experimental test of hyperstability, using largemouth bass as a model species to test for the causes of hyperstability.* The experiment was conducted on Camp Lake in Vilas County, Wisconsin.

Weekly standardized angling, followed by controlled largemouth bass removals, allowed researchers to measure angler catch rates at different largemouth bass abundances. In this case, angler catch rates remained fairly high over a wide range of bass population sizes and declined sharply only at very low population levels. Hyperstability can occur when anglers target spawning aggregations, when fishing technology improves, and with variation in angler skill. By controlling for these mechanisms, the team determined that anglers targeting preferred habitat, such as fallen trees and vegetated shorelines, gave rise to hyperstable catch rates.

Through this experiment and other studies, researchers have documented hyperstability in a wide range of species such as rainbow trout, walleye, and panfish. This suggests that the phenomenon may be common in harvest-oriented fisheries. Since angler catch may be a poor indicator of fishery health in certain situations, other standardized population assessment methods such as electrofishing may be necessary to help managers monitor fish numbers, and if needed, trigger an appropriate response to head off fishery collapse.

–Colin J. Dassow and Dr. Greg G. Sass

*Dassow, C. J., A. J. Ross, O. P. Jensen, G. G. Sass, B. T. van Poorten, C. T. Solomon, and S. E. Jones. 2020. Experimental demonstration of catch hyperstability from habitat aggregation, not effort sorting, in a recreational fishery. Can. J. Fish. Aquat. Sci. 77:762-769.

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From the Field: How Many Catfish Are in a River?

Have you ever wondered how many catfish are in the river where you like to fish? Biologists can answer that question by mark-recapture population estimation, which involves capturing and marking a large number of fish and then counting the number of marked and unmarked fish in a second sample. The population estimate also allows estimation of mortality rate and other population parameters.

Although simple in concept, precise population estimates require capturing and recapturing large numbers of fish and, therefore, are time consuming and expensive. Estimates of riverine populations are further complicated because the systems are “open” to movement into and out of a reach of river. This open condition is especially problematic for a species like channel catfish that is generally considered highly mobile.

Advances in statistical analysis of mark-recapture data that account for movement of fish allowed Nebraska Game and Parks Commission and University of Nebraska fishery researchers to estimate population size and other important population metrics of channel catfish in two 6-mile long sections of the Platte River, Nebraska.* The two reaches were similar in river width and channel pattern, but the upper reach was subject to daily fluctuations in water discharge from an upstream hydroelectric dam.

Population estimates for channel catfish larger than 8 inches were 2,315 and 3,913 per mile in the upper reach and 1,336 and 1,874 per mile in the lower reach during the two years of study. Annual survival was 49 percent in the upper reach and 13 percent in the lower reach. Among both reaches, anglers reported capturing 3 percent of the tagged fish, and 54 percent of these were harvested.

The average lengths of channel cats were similar between the two reaches, but a greater proportion of the population was 8 to 16 inches long in the upper reach, and a greater proportion of the population was 16 to 24 inches in the lower reach.

The annual survival estimates for the reaches in the Platte are low compared to estimates from other populations. The researchers attributed the high mortality to the unstable hydrologic conditions, high rates of emigration from the study areas, and angler harvest. Which of these factors or interaction of factors accounts for the low survival cannot be determined, but channel catfish over 16 inches were less than 15 percent of the estimated population in both reaches. The high harvest rate (54 percent) coupled with heavy fishing effort likely account for much of the low survival and the small size structure.

–Dr. Hal Schramm

*Blank, A. J., M. J. Hamel, J. J. Spurgeon, and M. A. Pegg. 2017. Assessment of a channel catfish population in a large open river system. Fish. Manag. Ecol. 24:460-468.

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