Michigan Trout Unlimited
MICHIGAN Trout
Trout Lake Suitability
16
by Tim Cwalinski, Michigan DNR
Spring 2021
Most anglers reading this magazine are likely Trout Unlimited members who have devoted hours feeding their trout passion fishing streams and rivers. If you are like me, that is where you cut your teeth. I recall crawling down the Allegheny Mountains slopes in Pennsylvania to flip a worm or salamander in a small creek that was not even called a creek but a run. When we think trout, our minds generally float to a lotic system, not one with standing water. Michigan is blessed with cold and cool water streams that hold variable numbers and sizes of trout. Yet, Michigan has a significant number of managed trout lakes as well, most of which are stocked, but a few hold wild trout. Likely, many stream anglers have never fished for trout in a Michigan inland lake. Like our streams, trout lakes are highly variable in morphology, depth, temperature, dissolved oxygen regimes, and management practices. Some lakes have excellent holdover of trout (stocked or wild) from year to year, and others that are marginal may display better holdover in certain years. Throughout my career, I have received many phone calls and emails from anglers searching for the right fish to stock in their waterbody. This has involved inquiries for both private and public lakes and certainly a fair number of private ponds. In most cases, stocking of any fish species was not warranted in the waterbody, which was undoubtedly the case for trout in most instances. There have been many requests to stock trout, despite these ponds or lakes not having the right “ingredients.” Maybe it is the romanticism that trout provide that fueled these inquiries. They certainly are more eye-catching than most of our standard warm and cool water species. Trout life is not easy. It certainly isn’t in a stream environment. Think about it—waiting for periodic episodes of food, dealing with larger trout that want you for dinner, and surviving and trying to put on muscle mass through periods of very cold water or periods of warm water. However, moving water may be the toughest or at least most constant hurdle from a bioenergetics viewpoint. Fish in stream environments are constantly on the treadmill, burning energy while still trying to grow at the same time. That is a tough balance. Lakes certainly offer an alternative lifestyle to this; almost easy living. Lakes that support trout typically support excellent growth. There is less energy demand for gonadal development, or what is developed is often shed
or reabsorbed. Thus, more conversion to body fat and size. Sounds great; it sounds like trout living in lakes have it made. However, lake life is not all glamorous for trout. Some of the reasons are obvious, while others are less obvious. As fisheries managers, we have many things to consider before stocking trout in lakes or evaluating a stocking effort. These include predators, lake depth, and summer dissolved oxygen and temperature profiles. One of the obvious questions is how many predators in the lake will eat “silver bullets” once they are stocked? Trout survive best in lakes where predators are low or absent. This is both from a competitive and predation standpoint. Bass, northern pike, and walleye will all feed on trout. Panfish will compete with trout for limited resources. Fisheries managers must narrow down our trout stocking efforts to lakes with limited or no warm or cool water species present. Stocking can occur in lakes with other species present, but they are typically confined to very large water bodies where fish can spread out thermally for parts of the year (i.e., Higgins Lake). Lake depth and the presence of a highly oxygenated summer thermocline are probably the most important factors determining trout survival in lakes. Trout need highly oxygenated cold water to make it through the warm summer months in lakes. Shallow lakes do not typically have a summer thermocline; thus, trout are limited by the absence of cold water from June through early September. That rules out many Michigan lakes and ponds for the presence of trout. Many lakes have a thermocline, yet the thermocline’s dissolved oxygen requirements (colder water) are the limiting factor. This is especially true for lakes with organic substrates and decaying aquatic vegetation, which often strips the dissolved oxygen from the thermocline. Fish breathe dissolved oxygen in the water through their gills. I use the 6 part per million rule for examining dissolved oxygen in the water column. Fish generally need this amount or more diffused in the water to survive and grow. Trout often need even higher amounts of dissolved oxygen, sometimes present in or near the thermocline. In many lakes, dissolved oxygen will plummet below the thermocline. Thus, cold or cooler water for summer refuge may be present, but oxygen is limiting or absent. Deep lakes with limited shoreline development or small watershed drainages can often possess both cold water and
