Bits & Pieces: Bass Feeding, Lake Trout Spawning, and Winter Pike

The Nature of Fish: Largemouth Bass Feeding Mechanics

Largemouth bass capture–meaning ingest or get into their mouth–prey two ways: ram feeding and suction feeding. Ram feeding is overtaking prey with mouth open. Suction feeding is quickly opening the jaws and enlarging the mouth cavity by lowering the tissues on the bottom of the mouth to create negative pressure that sucks water and the prey into the mouth cavity. A single feeding event is rarely all ram or all suction. Even with ram feeding, some amount of suction occurs in the last few milliseconds before the bass overtakes its prey.

Ram feeding predominates when bass are feeding on forage like minnows or shad in open water. Or maybe when they crush a crankbait, swimbait, or jerkbait. Capture of crayfish or a bottom-hugging fish is mostly suction feeding. The light tap or twitch in the line when they suck up a soft plastic from the bottom is probably suction feeding. A bass blows up on a topwater. Mostly ram feeding. But sometimes they just sip it from the surface. Suction feeding.

But how a bass detects prey also determines how they capture it. Vision and the lateral-line system are the bass’ dominant senses for detecting prey. Both senses are used simultaneously to maximize feeding success in moderately clear water and in daylight, but bass can feed successfully relying only on vision or only the lateral line.

Proving this is simple. Bass in a tank in a completely dark room can feed using only the lateral-line system. Chemically block the receptors of the lateral-line system (non-toxic cobalt chloride blocks neural transmission from the lateral-line sensory cells without blocking any other neural transmission) and a bass in a lighted tank can feed. Bass in a dark tank with a chemically blocked lateral-line system will not feed.

A little bit on fish anatomy may help you understand how the lateral-line system is involved in feeding. Most anglers have observed the lateral line as a slightly arched line on each side of the bass from behind the gill covers to near the tail. What you’re seeing is a line of scales with pores (holes) that allows water to flow through a canal under the pored scales; the sensory cells in the canal detect the water movement. Not visible without magnification and careful searching is an elaborate system of lateral-line canals on the head and jaws of the bass. A bass may get some information about nearby prey, and especially potential predators, from the sensory cells on its side; but it is the lateral-line system on the head of the fish that provides fine-tuned information about the position of the prey. The system is sensitive enough for a bass to track a prey fish by the turbulence trail it produces as it swims.

University of South Florida researchers Drs. Jayne Gardiner and Philip Motta discovered that the mechanics of how bass actually capture prey can differ depending on which sensory modality—vision or the lateral line—is in operation.* The study measured the capture of mosquitofish by 4- to 5-inch largemouth bass.

Using infrared light, which bass cannot see, and high-speed videography, the researchers measured numerous variables associated with approach to the prey and when the mouth opened to create suction. Strike distance was shorter and strike velocity was slower when bass could not see. The simple summary is that bass without vision relied more on suction feeding, whereas bass without lateral-line sensory information relied more on ram feeding. Ram feeding was even more prevalent for bass that received both vision and lateral-line information.

Bass are extremely well adapted for feeding in a range of light conditions, including total darkness. What I, as a biologist, find fascinating is that bass use a range of options to capture prey successfully depending on the sensory input. What I, as an angler, find fascinating—but also a bit intimidating—is that the final act of capturing the prey occurs in only 30 to 40 milliseconds, roughly one thirtieth of a second. If you think you have a fast hook-set, think again.

-Dr. Hal Schramm

*Gardiner, J. M. and P. J. Motta. 2012. Largemouth bass (Micropterus salmoides) switch feeding modalities in response to sensory deprivation. Zoology 115:78-83.

Field Science: New Look at Lake Trout Spawning

For many years, biologists have known that lake trout and other species of char spawn in the fall, typically as lake temperatures fall into the low-50°F range between late September and early December. Lakers inhabit large deep lakes where year-round coldwater refuges exist, mostly in the Great Lakes region and in northern Canada. Lake trout numbers have been rebounding in Lake Superior over the last 25 years due to sea lamprey control efforts, stocking, and restricting commercial fishing and fish are reproducing naturally.

The specifics of lake trout spawning have remained vague, however, since it usually occurs at night when late-fall conditions can be challenging, and many populations spawn on offshore reefs in large lakes. In some systems, adults also spawn in streams that feed large lakes.

Recently, a team of scientists from several agencies used acoustic telemetry to reveal siscowets (a fatty subspecies of laker that occupies very deep water) spawning in spring in Lake Superior at depths over 300 feet where they tracked the fish to specific areas around Isle Royale in spring. To more closely study this population, the Michigan Department of Natural Resources (MIDNR) began using a remotely operated vehicle (ROV) to record images and collect samples. In June of 2021, the MIDNR Research Vessel Lake Char was monitoring lakers around Isle Royale with the ROV and filmed siscowet lake trout spawning on rocky areas deeper than 400 feet on their north side of Isle Royale. The ROV was also able to collect viable eggs from the site to verify spawning and collect sculpins as well as small lake trout with eggs in their stomachs. Remaining questions involve the adaptations needed for hatchling char to survive such a harsh environment.

These findings expand our knowledge of the complex spawning strategies of lake trout and demonstrate the variability that occurs in fish behavior in different habitats and over time. It should also provide a tool for more accurately monitoring and managing these magnificent fish.

-Steve Quinn

Research Notes: Winter Pike Observations

Wisconsin DNR biologists studied habitat use, activity, and vulnerability to angling of pike outfitted with radio transmitters in a 220-acre lake from October through December.* The lake has a maximum depth of 22 feet, with submerged vegetation (cabbage, or pondweed) covering 36 percent of the lake down to 11 feet. Wild rice and bulrush covered 8 percent of the surface area. While only four pike were tracked, the study yielded interesting observations of these individual pike:

• All four pike preferred areas with aquatic vegetation at depths of 5 to 10 feet from October 1 to November 23.
• Activity areas ranged from 3.3 to 10.9 acres during 39 days preceding ice formation (October 1 to November 9). During ice formation (November 12-20), their ranges extended as they departed vegetated areas to deeper (18 to 22 feet deep) unvegetated areas.
• By November 23, 3 inches of ice had formed, and all four pike had returned to the littoral areas they had previously occupied.
• Pike activity under ice cover was greatest during daylight hours and decreased substantially during darkness (4:30 p.m. to 7:00 a.m.).
• Most activity under the ice was associated with aquatic vegetation, and pike presumably did not venture from the outer edge of vegetation.
• At the conclusion of the study, angling was used recover transmitters from three pike (one pike’s transmitter had expired). The initial strategy was to locate the signal and set up several tip-ups near the fish location (within 12 to 15 feet). This method was successful on the first pike.
• For the other two pike, holes were opened directly above the fish location in 8 to 9 feet of water. The first pike bit a jig and minnow within 10 seconds. The second pike didn’t respond to the bait for 30 minutes, even though the radio signal indicated that it was in the immediate area. On another attempt two days later the pike struck a jig and minnow within 10 seconds, but wasn’t hooked. It had moved 10 feet and had become stationary. After a new hole was opened at this location, the pike struck a live minnow and was caught.
• Use of an ice bar or auger to open holes in 3 to 5 inches of ice didn’t appear to cause pike to leave the immediate area or prevent them from feeding. Also, the two pike that weren’t hooked the first time they took the bait didn’t become wary and attempted to feed again shortly afterward.

-In-Fisherman

*Margenau, T. 1986. Habitat preference and movement of northern pike during fall and early winter in Potato Lake, Washburn County. Wisconsin Department of Natural Resources Research Report 186.

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