Tennesee’s Wild Side Weekly Article

The Age Of Fish and Why Catching the Big One Is So Challenging

By Bill Reeves, Director of Fisheries, TWRA

With the best months for bass fishing upon us, I am often reminded of the common misconception many anglers have regarding bass growth and age. Have you ever caught and released an 8-12 inch bass and assumed it was from the previous year’s spawn? Many folks have coined these fish “yearlings” or even “buck bass.” They are not likely to be “yearlings” and I’m not sure what a “buck bass” is.

Studies by TWRA and many other agencies show that bass growth is highly variable between species and years. First, not all species grow at the same rate. In general, largemouth grow the fastest. Our spotted bass, locally known as “Kentucky Spots,” have higher mortality and slower growth than largemouth or smallmouth in comparable waters. They rarely exceed 4-6 years of age and 15-18 inches in length.

For all black bass, first year growth is usually the most variable, depending to a great extent on how rapidly the water warms in the spring, summer rainfall, fertility of the water body, and several other factors. Generally speaking, good bass growth in Tennessee will be 6-8 inches by the spring following the year of their hatch, 8-12 inches by their second birthdate, and 10-14 inches by their third.

In waters where growth is not as rapid, bass may only be 3 inches on their first birthday and that limited first-year growth will follow them throughout their life. Five or six year old fish may be only 14 or 15 inches long. As you can see from this information, a 12-inch bass may be only two years old or it may be 5 years old, depending on where you catch it and the many other factors affecting ehse populations.

So, you might ask, how old is a 5-pound bass and why aren’t there more for me to catch? If the population is rapidly growing, a 5-pound bass might be as young as six to seven years. In slower growing populations, the fish might be 10 years of age or older.

So you can begin to see that part of the reason so few big fish are present in public waters is that they are generally old or very old and fewer fish survive through the years to old age, just like us humans. This brings us to a discussion, briefly, about mortality in fish populations. Fisheries scientists partition mortality into two components - first, from natural causes and, second, as a result of fishing, be it sport of commercial. Natural mortality and fishing mortality are additive and equal total mortality and we report as an annual occurrence even though is is an on-going process.

With bass populations, the natural mortality can be as high as 20 per cent per year or more, even in unfinished bass populations. We have very little impact on natural mortality, but in most cases we can have an effect on fishing mortality through regulations that limit harvest and support catch and release.

The total annual mortality rate of a given bass population can be as high as 50-70 per cent (30-40 per cent fishing mortality).

If we care a simple model of hypothetical, good growth, population of 1,000 age=1 bass with a 50 per cent total annual mortality at the end of their fifth year of life, only 32 fish remain at about 5 pounds (only 4 remain on 70 per cent).

Compare that to a similar population with no mortality from fishing (20 per cent annual mortality) and with the same 1,000 age-1 fish at the start, a whopping 164 would be alive at the end of the fifth year. Could this be the origin of the honey-hole concept of excellent fishing in un-fished waters?

Catching a large bass is a notable feat in anyone’s life. Now you know why and just how exceptional the opportunity and experience is. When you consider that larger fish may be less vulnerable to hooking... but that’s another story.

TWRA recognized anglers who have caught big fish, bass and many other species through its state record fish and TARP programs. For more information, contact your regional office or click into our website at www.tnwildlife.org.

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