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Bits & Pieces: Live-Imaging Versus Crappies, Economics, and a Giant Sunfish

Blending fishery science with everyday fishing.

Bits & Pieces: Live-Imaging Versus Crappies, Economics, and a Giant Sunfish

A carefully controlled experiment on Kansas's Cedar Bluff Reservoir sought to investigage the effects of live-imaging sonar. (Eric Engbretson photo)

From the Field: Live-Imaging and the Fate of Crappie Fisheries

There’s a lot of chatter these days about live-imaging sonar (aka, live-scope, forward-facing sonar). Live-imaging sonar (LIS) has been quickly adopted by many crappie anglers; and there is concern among anglers, guides, and fishery managers that the increasingly common use of LIS may cause declines in crappie populations. Kansas fishery scientists decided to replace concern with data.*

In a carefully controlled experiment on 4,900-acre Cedar Bluff Reservoir, a popular Kansas crappie fishery, 16 two-angler teams fished the reservoir for two days during November 29 to December 9. Each team fished one day with LIS and one day without. The side of the reservoir (north or south) and use of LIS (LIS or no LIS) was randomly determined for each team’s first day of fishing; on their second day, they fished the other side of the reservoir and the alternate use or no use of LIS. The anglers were all at least moderately skilled crappie anglers experienced with winter open-water crappie fishing, and one angler in each team was skilled in the use of LIS. The anglers fished from identical boats fully rigged with chartplotting, down-imaging, and side-imaging electronics in addition to LIS. Use of all electronics except LIS was allowed on all days. Catch of black and white crappies were combined for analysis.

Anglers fished 448 hours and captured 205 crappies. Average catch rate per angling team per day was 6.9 crappies for teams using LIS and 5.9 crappies when not using LIS. Average size of crappies caught by anglers using LIS was 11.2 inches, 10.8 inches for anglers not using LIS. The small differences in catch rate and size were not statistically significant. Differences in catches between sides of the lake also were not different. Conclusion: LIS does not significantly improve crappie catch rate or size of catch. And also important: LIS does not make a crappie fishery more vulnerable to the effects of exploitation.

These results are for only one fishery and for a rather brief period of time, but the study does look at the winter open-water fishery, a time when crappies are often scattered and, ostensibly, LIS can be useful. With data in hand showing no increase in catch rate or fish size using LIS, the study authors astutely suggest that at least some of the concern about LIS is driven by social forces, particularly frequent postings on social media of pictures or reports of big crappies or large catches caught using LIS, that can lead to very embellished conclusions about the effectiveness of LIS. Nobody posts pictures of fish they don’t catch.

--Dr. Hal Schramm

*Neely, B. C., J. D. Koch, and K. B. Gido. 2023. Evaluating effects of live-imaging sonar on angler catch of crappies in a Kansas impoundment. Fisheries 48:49-53.

By the Numbers: Sportfishing’s Economic Impacts

The American Sportfishing Association (ASA) released the 2023 Economic Contributions of Recreational Fishing: U.S. Congressional Districts report, an update of previous data collected by ASA in partnership with Southwick Associates. The report shows angler participation and economic impacts for all 50 states and 435 U.S. congressional districts.

According to the report, America’s 52.4 million anglers contribute $148 billion in economic output and support 945,500 jobs across the U.S., while also contributing $1.8 billion toward conservation. Jobs supported include those in manufacturing and sales of fishing equipment and gear, as well as in additional industries such as lodging, restaurants, charter trips, and more.

To see the full report and information for each U.S. congressional district, visit asafishing.org/economic-impacts-of-recreational-fishing.

--In-Fisherman

Top 5 States: Economic Output

  • Florida: $13.9 billion
  • Texas: $7.7 billion
  • California: $6.2 billion
  • Minnesota: $4.2 billion
  • Michigan: $3.9 billion

Top 5 States: Percentage of Population That Fishes

Recommended


  • Alaska: 64%
  • Wyoming: 58%
  • South Dakota: 48%
  • Rhode Island: 39%
  • Oklahoma: 37%

Top 5 U.S. Congressional Districts: Economic Output

  • AK At Large: $815.6 million
  • MN District-8: $631.8 million
  • MN District-7: $589.7 million
  • WY At Large: $568.3 million
  • SD At Large: $558.5 million

Top 5 U.S. Congressional Districts: Percent Population That Fishes

  • Alaska At Large: 63%
  • Wyoming At Large: 58%
  • South Dakota At Large: 47%
  • Wisconsin District-7: 42%
  • Minnesota District-8: 41%

Aquatic Discoveries: The World’s Biggest Bony Fish

A mola mola ocean sunfish in the water.
The giant sunfish is the largest of three ocean sunfishes found in the world’s oceans. Doug Perrine photographed this specimen of Mola mola off Vancouver Island. (Doug Perrine photo)

In December 2021, local fishermen came across a huge fish carcass floating near an island in the Azores archipelago, a part of Portugal. They were astounded but fortunately were able to notify scientific authorities who collected it and determined it was a giant sunfish Mola alexandrini. They towed it to port and using a scale mounted on a crane, they determined its weight at 6,050 pounds, the heaviest bony fish ever collected. It was 10.6 feet long and broke the weight record for a specimen of the same species caught off Japan.

This species of ocean sunfish is largest of three found in the world’s oceans. All swim slowly near the surface propelled by extremely long dorsal and anal fins that paddle together to propel the giant fish slowly along. Their caudal fin is curled inward to create a scalloped rear portion that functions like a rudder. Though usually spotted on top, where they sometimes swim parallel to the surface to absorb the sun’s rays, they’re known to dive to depths over 500 feet. “Mola” translates from Latin as “millstone” in reference to their round bodies.

A diet of jellies, squids, small fish, crustaceans, and algae fuel their amazing growth. Beginning life as a 1/4-inch larvae, ocean sunfish increase weight by more than 80 million times to adult size of more than a ton. Scientists believed the Azores specimen to be female and estimated its age at over 20 years. They’re thought to be most closely related to the pufferfishes. This lineage is more obvious in young specimens, as they’re round-shaped and have spines, before morphing into the far-different adults.

 --Steve Quinn




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