“Ten percent of the fishermen catch ninety percent of the fish” is a fishing adage of uncertain origin. “Surveys made by biologists show that ten percent of the fishermen catch ninety percent of the fish” was cited in print in 1956. “It is said that 10% of the fishermen catch 90% of the fish” was cited in print in 1960.
 
The ten percent of fishermen (called “10 percenters”) have more skill and better equipment that help them catch so many more fish.
 
   
24 September 1951, Sandusky (OH) Register-Star-News, pg. 14, col. 3:
The measure would also ask for a substantial increase in commercial fishing licenses because they now only pay $46,000 yearly yet catch 90 percent of the fish in comparison to the millions paid by hook and line fishermen who only land 10 percent of the fish.
 
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April 1956, Boys’ Life, “Start Fishing” by Tom Warner, pg. 13:
Surveys made by biologists show that ten percent of the fishermen catch ninety percent of the fish.
 
13 May 1960, Boston (MA) Traveler, “Phooey to Fishermen’s Luck,” pg. 35, col. 1:
It is said that 10% of the fishermen catch 90% of the fish. This is most likely because the anglers in that 10% know more than a few tricks of the trade.
 
29 June 1960, Thomasville (GA) Times-Enterprise, “Skill More Than Luck Accounts For Success Of Some Fishermen” by Sammy Glassman, pg. 16, ol. 1:
It has been said that only 10 percent of the anglers catch 90 percent of the fish. There’s no way to really prove this theory. But It is an established fact that some fishermen have a knack for making big hauls. Is it luck, or is it skill?
 
5 August 1962, Cedar Rapids (IA) Gazette, “Forest, Field and Stream” by Russ Graham, pg. 4D, col. 1:
Often we hear that 10% of the fishermen catch 90% of the fish. One reason for this is that those in the 10% class of winners are the ones that are fishing waters they know.
   
13 April 1967, The Plain Dealer (Cleveland, OH), “Fishermen Stalk Largemouths as Top Bass Trophy” by Lou Gale, pg. 78, col. 2:
BE A HUNTER—If you want to join the 10 percent of our fishermen who catch 90 percent of the fish, you have to hunt your fish at any given hour.
 
6 July 1967, The Plain Dealer (Cleveland, OH), “Fishing Pros Back ‘Luck” With System” by Lou Gale, pg. 39, col. 1:
Now that another hot (?) summer is here we will see the sport fishing “pros,” who are 10% of our anglers, catch 90% of the fish.
 
That leaves 90% of the fishermen catching only 10% of the fish.
 
19 June 1972, The Plain Dealer (Cleveland, OH), “Directory Lists Lakes,” Magazine, pg. 11, col. 1:
A new directory of the 1,600 mapped Wisconsin lakes should help any angler enter the charmed circle of experts—the 10% of all fishermen who are said to consistently catch 90% of the fish taken.
 
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The Sky Fisherman
By Craig Lesley
New York, NY: Permissions, Houghton Mifflin Company
1995
Pg. 92:
Jake’s rule of thumb was ten percent of the fishermen catch ninety percent of the fish.
 
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Trout Dreams
By James Merritt
Lanham, MD: The Derrydale Press
2000
Pg. 63:
“It’s a truism that 10 percent of the fishermen catch 90 percent of the fish—and I further believe that 1 percent of those fishermen catch 90 percent of the big fish.”
 
Ifish Fishing and Hunting
SCStinger 
06-28-2006, 01:48 PM
10 percenters
The way I see it if the 10% that catch 90% of the fish would take up golf then there would be more fish than you shake a pole at.
 
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Walleye, The Moving Target
By R. G. Webb
Xlibris Corporation (Xlibris.com)
2011
Pg. ?:
Have you heard the old adage that ninety percent of the fishermen catch 10% of the fish, and 10% of the fishermen catch ninety percent of the fish? Well, that old adage is true.
   
Curry Coastal Pilot (Brookings, OR)
Catch more fish: Become a 2 percenter
Written by Larry Ellis, fishing columnist  
January 04, 2014 10:37 am
(...)
There’s an old adage that says, “10 percent of the fishermen catch 90 percent of the fish.” They call these people, oddly enough, “10 percenters.”