Trophy Fish What Makes Em’ Grow

By Ben Leal

As a lifelong angler I have had the thrill of catching some genuine trophy fish. As a boy, a trophy was anything bigger than the last fish I caught. And in one case it was one that never took the bait, but one I could clearly see as it gave some serious consideration to the cheese ball I was offering on the other end of my line. In my young eyes it was massive!

My angling endeavors have also taken me across the continental United States and in to Canada. I’ve seen and caught some incredible fish, some that have reached what we as adults would consider trophy size. Each one leaves a lasting memory and with the advent of digital technology and the internet, trophies are shared among friends and families. And in many cases those trophies are released to swim another day, forever etched in the angler’s memory.

What is it that makes these fish trophies? What factors throughout North America provides us with countless memories and hours of angling fun? And what can we do as outdoors men and women to help maintain these fisheries?
“One of the most important factors when it comes to growth is water temperature”, said Iowa Department of Natural Resources Fisheries Biologist Ben Dodd. “Fish are cold blooded, so it determines their metabolism and the length of the growing season.”

This “growing season”, is the time of year where water temperatures are at the optimum and fish feed more frequently. Bass for example tend to grow larger in the southern reaches of the U.S. due to the longer periods of warm weather. In fact largemouth bass fry growth is directly related with water temperatures. Largemouth bass fry maximum growth occurs at temperatures between 81.5 to 86 degrees. Adult largemouth bass prefer water temps ranging from 77 – 80 degrees and will work to find cooler water as summer progresses. “When water temps get too high, fish will actually stop feeding”, added Dodd.

Depending on what part of the Country you’re in, bass will have an average life span of about 16 years, though it’s likely less here in Iowa. This shorter growing season in Iowa may lead to the reason why the record largemouth bass of 10 pounds, 12 ounces caught in Lake Fisher in 1984 has stood for 32 years.

Walleye grow larger the father North you go. The life expectancy of walleye, again depending on location varies from 5 – 7 years in southerly warmer climates and 12 – 15 years in northern areas. Generally, and I use that word loosely due to a variety of factors, a walleye will grow to about 5 inches in its first year. By year five these fish will reach about 14 inches in length and weigh about a pound. Move on to a 10 year old fish and you’re looking at a fish that is about 19 inches long and weighs in about 2.6 pounds or so.

In an ideal fishery a walleye that reaches 25 years of age will measure out to about 29 inches and weight between 9 and 10 pounds. For many, a fish that size is considered a fish of a lifetime. Walleye thrive in cooler deeper lakes and reservoirs where summer water temps hover at 65 – 70 degrees for longer periods of time. You are more likely to catch a trophy sized fish in northern Iowa, Minnesota and Canada due to cooler summer temps as well as the depth of area lakes.

Management Practices
We’ve taken a look at growth rates as well as what is considered the growing season, but what else can we do to help fish reach these sizes, especially in Iowa. Catch and release has really become more of the norm that it used to be. Now about 80 percent of anglers are releasing most of their fish and many practice CPR; Catch, Photo, Release. Putting larger trophy fish back in the fishery helps maintain a good brood stock.

In Iowa there are quite a few bodies of water that have implemented slot limits. Generally, the purpose behind the implementation of protected slot limits is to improve the angling opportunities in a particular body or bodies of water. Protected slot limits are most often used to regulate the harvest from waters where natural reproduction occurs. The protected slot limit is set in such a way that it protects the size of those fish deemed most important to the species spawning success in that fishery. With the size of the most sexually productive fish protected from harvest it is likely that an increased number will spawn during a given year and hence lead to more naturally produced individuals. In addition to improving natural reproduction success the protected slot limit can also serve to improve the average catchable size.

Recruitment is the number of young fish that survive to adulthood. Lakes with 20 – 40 percent coverage of aquatic plants usually have high recruitment. The aquatic vegetation provides shelter, protection and food for the young fry as they grow, giving them a great chance of reaching one year of age. Lakes like Big Creek have benefitted from habitat that is submerged as ice leaves the lake. Trees are tied together along with a few cinder blocks and once on the lake bottom, provide habitat for young fish as they grow.

Water levels in lakes and reservoirs also have a positive and negative affect on the growth rate of fish. In a lake with low or poor recruitment, high water events will help improve the fishery by giving fry the opportunity to spend a longer amount of time in flooded timber and grassy areas. High water events also help improve the year class of some species like crappie or bluegill. These fish will spawn in shallow areas not readily accessible by boat or shore and are not part of the spring harvest that they might have otherwise been.

Red Rock for instance had a couple years of high water events in a row. Spring fishing was good, but fish were harder to reach and ultimately were not caught. A couple years later as water levels returned to normal, crappie averaging 12-14 inches or larger were harvested. Years where drought and low water levels occur, recruitment is low and mortality is high and in some cases entire lakes have a die off.

As anglers we can help improve growth rates in lakes that are overpopulated. Though this is more likely going to be the case in smaller bodies of water and ponds and managed by the Iowa DNR, but harvesting fish to reduce the population will improve the fishery. There are some lakes that have an overabundance of smaller fish. Anglers will simply put these back due to size, but because overpopulation they don’t grow. In a private body of water, introducing predatory fish can help improve fishery quality. Remember though that it is illegal to introduce any fish in to a body of water managed by the Iowa DNR, whether it’s a known inhabitant or not.

Environmental Factors
“Water quality can also have an impact on the caliber of a fishery”, adds Dodd. “Additionally factors such as low dissolved oxygen levels, a high or low pH, contamination, etc. can lead to poor growth or in some cases mortality.”

“Fish that are in the middle of their range tend to do better than those on the edge”, said Recycled Fish Executive Director Teeg Stouffer. “There are some exceptions to this; however in general that rule always applies”. Harvest and fishing pressure can lead to low quality of fish especially if overharvesting is an issue. Big fish need to eat as much as they can and expend the least amount of energy doing so. “The amount of available forage for these big fish is also a factor”, noted Stouffer.

The perfect scenario for growing big fish would be a body of water with great water quality, habitat for spawning as well as for the young fish of the year to survive. Once the fish reach adult age the habitat would need to support a strong population of these larger and older fish. Management of the fishery is incredibly important; a managed harvest plan, release of all big fish and again abundant food sources.

Management of our waterways from the smallest of streams to the biggest body of water in Iowa is everyone’s responsibility. The Iowa Department of Natural Resources is only but one link in the chain of fisheries management. As anglers we need to be fully aware of what we’re doing on the water as well as off the water. Follow guidelines for using and disposing of live bait, clean both your trailers and boats as you move from one body of water to another. And if need be, report those that are abusing the resource.

Iowa’s fisheries are an ever changing environment. Let’s take time to care for and be stewards of what we’ve had the privilege of using as adults so that our children and grandchildren can enjoy the same resource we have. Let’s leave it in better shape than we found it. Tight Lines All!