Lake Mary Ronan is one of Northwest Montana's favorite fishing holes. This 1,500-acre lake usually produces good catches of kokanee salmon and yellow perch, plus an occasional rainbow trout or largemouth bass.
One of the reasons for this lake's high-quality fishery is because Lake Mary Ronan is a fairly shallow lake. It is only 47 feet deep at its deepest spot, so the entire bottom is productive.
Due to a variety of aquatic conditions such as penetration of sunlight to the bottom and warmer water temperatures, shallow lakes usually have more vegetation and better habitat for the many micro-critters that provide food for game fish.
Lakes that are deep, with cold, clear water but less natural vegetation are pretty to look at but tend to be less productive for fish.
Originally, Lake Mary Ronan was fishless. Planting records go back to 1892 when cutthroat trout, peamouth and shiners were planted in the lake.
Over the next 100 years, the fish plants in Lake Mary Ronan read like a smorgasbord: Chinook salmon, coho salmon, rainbow, Yellowstone cutthroat, westslope cutthroat, kokanee, grayling, brook trout, largemouth bass, sunfish and yellow perch were stocked.
Those were the days when very little science was used in fish management. It was the attitude of "Let's dump some fish into the lake and see what happens!" What happened was mostly nothing.
Yellow perch were illegally planted in 1992. Before then, Lake Mary Ronan was probably the premier kokanee fishery in Montana.
When yellow perch were illegally introduced, most fishermen and fishery biologists predicted the kokanee population would crash. Well, that hasn't exactly happened.
Prior to the introduction of perch, fish studies in 1992 indicated that kokanee represented 77 percent of the fish biomass in the lake. By 2005, the newly introduced perch represented 91 percent of the fish biomass and kokanee represented only 6 percent. At first glance, that would seem to indicate that very few kokanee remain.
Not so! Yellow perch seem to have tilled a vacant niche in the lake's ecological makeup.
Fish nets put out by fishery biologists to sample fish populations found as many kokanee in 2003 and 2005 as were captured by similar sampling done during the years preceding the introduction of perch.
Very little natural reproduction of kokanee occurs in Lake Mary Ronan, so fish biologists stock about 400,000 kokanee each year in this lake. To minimize predation by perch, the new stocking strategy is to plant 200,000 larger kokanee, over 3 inches long.
Good kokanee fishing is important to biologists, but even more important is having Lake Mary Ronan as the egg source for most statewide kokanee stocking programs.
Another interesting aspect of Lake Mary Ronan fish management is that rainbow trout have not been stocked since 1974. But natural reproduction since 1974 has produced enough rainbow to provide some fish for fishermen.
When rainbow stocking stopped in 1974, about 50,000 4- to 6-inch westslope cutthroat trout were stocked every year. Yet even with this consistent stocking of larger cutthroat trout, very few cutthroats are caught by fishermen.
What's happening to the cutthroats?
One of my favorite fish stories occurred on Lake Mary Ronan several years ago. Five of us were ice fishing for kokanee. We were fishing on the bottom in 35 feet of water and barely catching enough fish to keep us at that depth. Then I remembered my new fish finder.
The fish finder showed schools of fish at 15 feet. We pulled our baits up to 15 feet and suddenly fishing was red-hot. Within an hour, we had our 50 kokanee limit and one rainbow.
So Lake Mary Ronan remains as one of my favorite lakes for good fishing.