PINE BLUFF — One of the difficulties of raising fish is that it is difficult to see how they are growing without capturing several for inspection, Scott Jones, small impoundment Extension specialist at the University of Arkansas at Pine Bluff, said. Additionally, in fishing ponds, there are often several species being grown in the same space.
Fortunately, there are some simple sampling techniques, measurements and calculations that can be performed to help determine the health and balance of the fishery.
“The easiest strategy to assess the health of your fishery is to hire a lake/pond management company to sample the pond,” Jones said. “This can be costly, but it also puts your fishery in the hands of a professional who can quickly inspect the fishery and prescribe solutions.”
To assess the fishery yourself, you will need a fishing rod(s) suitable to catch adults of all the species in your pond; bluegill and largemouth bass tend to be the most common. You will need lures/bait appropriate for those species.
“For example, adult bluegill can be caught with nightcrawler worms on a size 6 to 8 hook under a floating cork/bobber,” he said. “Largemouth can be caught with a variety of artificial lures, but a green pumpkin colored 6-to-8-inch plastic straight or ribbon-tailed worm on a Texas-rigged bullet weight (1/8-3/8 oz) and hook (2/0-4/0 size) will consistently produce bites.”
Try to catch at least 20 to 30 largemouth and 50 bluegills for a good sample. Use sharp scissors to snip a small section of one pelvic fin off to mark each captured fish if you plan to release them; recapturing and remeasuring a fish interferes with results.
“These fins will grow back, and it does not harm them or significantly interfere with swimming,” Jones said. “For each captured fish, measure and record their length with mouth closed and tail pinched (in inches or millimeters) and weight (in pounds or grams).”
A seine net can also provide valuable insights into reproduction stability. Nets 20 feet long by 5 feet tall with 1/4-to-1/3-inch mesh do well. In spring, when the water reaches about 70°F consistently, drag the seine down the bank in shallow areas for 30 to 50 feet in 3 to 5 different places.
“At the end of your drags, have the person away from the shore walk towards the shore creating a semi-circle in the net as they approach. When they reach the shore, pull the seine from the weighted bottom line starting at the ends of the net up the bank,” he said. “Move slowly enough that the weighted line does not rise off the pond bottom. If you move too quickly, pull the float line first, or pull the weighted line off the pond bottom, many of your fish will escape below the net.”
Once the net is completely on land, count and record the number of fish of each species caught, and roughly what size they are (in inches), before returning them to the pond. Results from both techniques are then combined to determine the condition of the fishery.
“If your seine hauls produce many recently hatched bluegills (less than 2 inches in length), some intermediate sized bluegill (2 to 4 inches), and some recently hatched largemouth (1 to 4 inches), then you likely have stable reproduction from both species suggesting that the fishery is balanced,” Jones said. “If your seine hauls produce no or very few recently hatched bluegills, many intermediate sized bluegills, and no recently hatched largemouth, it is possible the fishery is bluegill-crowded. If your seine hauls produce many recently hatched bluegills, no or very few intermediate sized bluegills and no or very few recently hatched largemouth, it is possible the fishery is crowded with largemouth bass.”
Fish length and weight data can be converted into “relative weights,” a measure of how plump a fish is compared to the standard for that species at a given length. The Alabama Cooperative Extension System has an easy to use online fish relative weight calculator that will do the conversions for you (https://www.aces.edu/blog/topics/fish-water/fish-relative-weight-calculator/).
“Select the species, whether you used metric or English measuring units, then type in the weight and length, and click ‘Calculate Relative Weight.’ The calculator will give you the relative weight for that fish and even tell you what that number means,” he said. “Relative weights (Wr) less than 80 are poor, 80-90 are average, 90-100 are good, 100+ are very good.”
The species average Wr gives clues to the fishery condition. If both largemouth and bluegill Wr are in the 90s or higher, the fishery is performing well and balanced. If bluegill Wr is very high and largemouth Wr is very low, it is likely the fishery is largemouth bass crowded. If largemouth Wr is very high and bluegill Wr is very low, it is likely the fishery is bluegill-crowded. If Wr for both species is very low, something else is wrong; usually either very poor water quality/fertility, excessive aquatic weed growth or excessively muddy water.
“Armed with this information, you can have a more productive conversation with a fisheries biologist and begin working on plans to maintain or improve fishery performance,” Jones said. “Resources like the Arkansas Game and Fish Commission, Arkansas Cooperative Extension fisheries specialists and private lake and pond management companies can use this information to help you develop a management plan.”
For more information about fishery assessment, contact Jones at (870) 575-8185 or joness@uapb.edu, or contact your local county Extension office.
The University of Arkansas at Pine Bluff offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
