What Muskies Eat: How Big, How Much, and Where?
There’s been some very interesting work done on muskie diets in the last five years. The muskie’s diet is important to us as anglers because it affects not only influences where we search for muskies but also the presentations we use when developing patterns. If muskies are primarily targeting ciscoes or whitefish at a certain time, species that tend to suspend over deep basins in cool water, we should be fishing in those same basins with lures that match the behavior of those prey species. If muskies are feeding on white suckers, we would do better to target structure with mud and sandy areas that are shallow enough to have oxygen at depth, using lures that hug the bottom. Even if you don’t try to exactly match the prey itself, knowing what prey muskies stalk will help you to develop the “where, when, and how” of your muskie strategy.
The recent muskie diet studies fall into two categories. In the first study is, researchers captured muskies, usually by electrofishing, and then flushed the muskie’s stomach to investigate what food items were present. This sort of study gives direct information about what muskies eat. The second study examined the muscle tissue of captured muskies to see how the contents of their muscles compare to the contents of tissue in their prey. It turns out that the nutrients given to muskies by eating ciscoes over deep water are measurably different from the nutrients they receive from consuming shallow-water prey such as bluegills, suckers, and perch. The old adage “you are what you eat” comes to mind here, and we could revise those words for muskies to say “they are WHERE they eat”!
Stomach Contents Study (Glade, et. al.)
The stomach contents study included a significant number of muskies of various sizes, and this was not limited to muskies of small size. In all, 368 muskies were captured as part of this study. What is more, the study was not limited to small muskies. 84 of the muskies sampled were larger than 42 inches in length, and 14 of the muskies were larger than 50 inches in length. These numbers are high enough that the researchers were able to come to clear conclusions about how muskies feed.
The size of prey items that muskies actually consume is an interesting question. A general rule I’ve heard spoken by anglers is that maximum prey size is about one-third the length of the muskie. The stomach contents of muskies have been able to provide confirmation of this general rule, however, there is significant variation in prey size. Muskies will definitely consume prey much smaller than one-third their length. However, it was also found that muskies will consume prey items up to one-half of their length. This was NOT limited to small muskies either. A decent number of muskies in the 50” to 55” size class were sampled, and they had prey items in their stomachs up to nearly 24” in length!
One of the aims of the diet study was to see how predator diets vary seasonally. For us muskie anglers, this is really important information because this knowledge can inform our lure choices by season; spring, summer, or fall. The research shows that there is no substantial variation in muskie diet throughout the season for muskies captured from shallow water. While there is some small variation in the importance of different types of prey, this variation was not large enough to be counted as significant. Thus, even though tradition suggests that we use small lures in the spring period, medium- to large-sized lures in summer period, and very large lures in the fall, the research suggests that muskies do not change much about their diet throughout the year. Instead, what is more important in lure selection is whether the lures we present are appropriate to the structure and depth that we are fishing rather than hewing to some traditional guideline on the size of the lure we should be using. So if muskies are in deeper water off a break line in the early part of the season, it is probably just fine to use a Magnum Bulldawg or even a “Pounder” for your presentation.
The diet study also compared the diets of muskies of various sizes. It did so by sorting the muskies by size class and breaking down the muskie’s food items by type within that size class. The size classes were 30”-38”, 38”-42”, 42”-50”, and 50+”. To estimate a food item’s importance, a careful analysis of food items was conducted accounting for both weight and number of each type of prey. This analysis was done to balance the situation where a muskie might eat 30 fathead minnows and 1 huge white sucker. The analysis took into account both numbers and weight of prey to assign a number to each type of prey item as to its importance in a muskie’s diet.
Yellow perch is an extremely important prey fish for many predators (muskies, walleyes, northern pike, etc…) in the northern tier of lakes. The study found that yellow perch were the single most important type of prey for muskies that were 30”-38” long. But this importance of yellow perch decreases significantly as muskies grow. For muskies in the 38”-42” size class, the importance of yellow perch as prey diminished while the importance of sunfish increased so that both perch and sunfish were about equal in importance. By the time muskies have grown into the 42”-50” size class, yellow perch importance has shrunk still further, and white suckers take the lead as the most prominent prey with other significant fractions of a muskie’s diet including northern pike, invertebrates (like worms and insects), and bullheads. By the time muskies are in excess of 50”, their diet has shifted to mostly white suckers, invertebrates, and bullheads. An important thing to know about muskies of large size (42” and larger) is that their diets are incredibly diverse, ranging from insects and worms to very large white suckers and other prey. This is quite different from muskies of smaller size, whose diet is dominated by yellow perch.
A nugget of information that struck me as I was reviewing this data is the types of prey items that dominated the diets of the largest muskies: white suckers, aquatic invertebrates, and bullheads. What do each of these prey items have in common? They all inhabit bottom areas of our lakes. Think carefully about that fact when you are considering what depth you want to cover with your presentations when targeting large muskies.
You may have noted the complete lack of pelagic forage (eg. ciscoes) in the muskie diets discussed in this section. Keep in mind that the study I’ve been writing about in this section was accomplished by electrofishing in the shallow regions of lakes. Since pelagic forage like ciscoes do not typically inhabit shallow areas, it is not surprising that the muskies sampled in this study didn’t show many ciscoes in their diet. After all, if a muskie is captured in the shallows it is less likely to have consumed a pelagic meal like a cisco.
Tissue Sampling Study (Herwig, et. al.)
The second study of muskie diets involved taking a small sample of muscle tissue from a captured muskie and analyzing the contents, comparing it to the contents of various prey items. These contents basically serve as a record of what (and where!) muskies had been feeding in the past few months. The muskies involved in this study were captured in the spring, so the tissue samples gave a record of what each muskie had consumed in the late summer into the late fall right before ice-up the previous year.
The types of prey signatures that were distinguishable in the data were: 1) invertebrates (worms and insects), 2) shallow-water prey fish (suckers, bluegills, perch, etc…), and 3) pelagic prey (ciscoes). The analysis of these tissue samples allowed the scientists to get the approximate mix of each class of prey in the collective diets of the capture muskies. As a check on their results, they analyzed muskies that were in lakes without ciscoes, and they found exactly what they expected: almost all of the muskies’ diets consisted of shallow-water prey fish with a small amount of invertebrates (and NO ciscoes). In lakes with small populations of ciscoes, they found that the muskie’s diets were approximately 80-85% shallow-water prey fish with the remainder of their diets being about an even mix of ciscoes and aquatic invertebrates. However, when they examined the tissue of muskies from lakes with significant cisco populations, they found that ciscoes accounted for about 50% of the muskie’s diets, with shallow-water prey fish coming in at about 25% of their diets, and aquatic invertebrates also contributing about 25% to their diets.
Unfortunately, the data that was presented didn’t single out individual muskies or sub-populations of muskies. These numbers were arrived at by analyzing the data of all sampled muskies in each lake together so that the researchers could get meaningful statistics. Thus, we don’t know if the data on cisco lakes mean that each muskie split its time (half the time eating ciscoes and half the time eating in the shallows) OR whether half the muskie population spent all its time in deep water eating ciscoes while the other half of the muskie population stayed in the shallows eating shallow water prey fish and invertebrates. It’s probably a mixture of both, but the data (as presented) are inconclusive on that.
Conclusions
What conclusions can we draw from these two classes of studies? First, the tissue-sampling study showed that muskie diets were highly dependent on the type of lake the muskies were living within. A fertile lake in the Twin Cities metro area had spring-caught muskies feeding almost exclusively on yellow bullheads in the months previous to their capture. On the other hand, spring-caught muskies in much less fertile lakes that had large numbers of ciscoes showed that ciscoes made up 50% of their diets.
Second, the stomach-pumping study showed that muskies captured in the shallows had lots of shallow-water prey and aquatic invertebrates in their stomachs, but very few pelagic prey like ciscoes (even for lakes that had significant cisco populations!). Let’s consider what this tells us about the idea that muskies engage in a daily migration: positioning in the shallows during low light periods and moving out to deeper, even pelagic, areas during bright conditions. If this idea of migration throughout the day is true, the data from the stomach-pumping study tells us that muskies that move out to deeper water don’t necessarily do so specifically to feed on ciscoes. If so, their stomach contents would have shown at least SOME ciscoes from the previous few days’ deep-water hunting. Instead, either the muskies are following prey as the prey themselves move out to deeper areas (perch and panfish sometimes do engage in such daily migration) OR muskies are moving out to deeper pelagic areas for reasons that are not prey-related (eg. to use it as a low-light or thermal refuge during midday). Which of these reasons is true should probably affect how you present to these mid-day, deep-water muskies.
Also, it was noticed in the stomach-pumping study that the diets of muskies and walleyes seemed to be somewhat similar to one another in the spring of the year. The main reason for this similarity was the out-sized prevalence of yellow perch in muskie diets at this time (muskies captured later in the year had fewer yellow perch in their stomachs). This observation, along with the inference we made that muskies concentrate their hunting efforts on cisco during the late fall, suggest something about muskie predation strategy. Yellow perch spawn early in the spring. Bluegills and crappies spawn in the early summer period. Ciscoes spawn in late fall. It seems that muskies tend to prioritize prey that are spawning. This makes good sense since spawning prey tends to be concentrated and distracted, obvious targets for opportunistic predators. While this isn’t necessarily a surprising conclusion, it does support the long-held notion that knowing about the habits of muskie’s prey will allow you to locate muskies!
Finally, the purpose of both of these studies was to gather data on the contention that muskies eat significant number of other game fish (like walleyes). Through both direct and indirect observation, both studies concluded that the importance of game fish to the muskies’ diet is very small compared to other types of prey. But the studies went further than this. They also sought to answer the question about the amount of competition for prey between the muskie population, the walleye population, and the northern pike population. It was established that muskies have the most diverse diet of all the game fish species (mostly because of muskies’ very large size). Muskies eat everything, from small insects to birds to large prey fish. Because of the diversity of the muskie diet, there was very little overlap between what muskies typically eat and what other game fish eat. For this reason, muskies can happily coexist with other game fish populations. Yes, muskies do eat the occasional walleye, northern pike, or bass, but as a population, muskies have little to no negative impact on the populations of other game fish species.
Hopefully this review of two of the latest studies on muskie diet have given you some food for thought when developing patterns this upcoming season.
Best of luck on the water!
Dr. Bob