Fly of the Year For 2007

• By Jason Hansen • Empirical Analysis

CDC Biot Thorax Dun
CDC Biot Thorax Dun

The 2007 year was the second consecutive year that I have recorded all of my fishing trips into Fish Swami. One of the benefits of keeping a fishing log for all of my outings is being able to view catch statistics for previous years. Fish Swami has a very powerful statistical analysis tool that lets you query your fishing log for almost any statistic you would like to know. I used that tool to compile the following table for my top 10 fish-producing flies for 2007.

Number Caught    Pattern   
68CDC Biot Thorax Dun
61Zebra Midge
50Pheasant Tail BH
49Disco Zebra Midgeling
40CDC Parachute
35Elk Hair Caddis
26Trigger Nymph (Mercer)
24Parachute Midge Emerger

I must make an immediate disclaimer: my fish catch numbers are influenced by a few important factors: I fish for rainbow and brown trout almost exclusively; I fish tailwater rivers the majority of the time; and I live in the Pacific Northwest. If any of these factors were different for 2007, my list of top 10 flies would change significantly. The fact that my top 10 list is dominated by mayfly and chironomid/midge patterns underscores the types of waters I fish and the species of fish I target.

CDC Biot Thorax Dun

The top pattern for me in 2007 was a CDC (from the French term cul-de-canard, meaning “duck butt”) derivation of a classic mayfly adult pattern, the Thorax Dun. I had not fished the CDC Biot Thorax Dun pattern much previous to 2007, catching only 3 fish on it the prior year. The difference in catch rates between the two years can be mainly attributed to my developing skills in matching mayfly hatches. These skills are in turn directly tied to me fishing more on tailwater rivers with good hatches and selective rainbow and brown trout, versus years past when I fished freestone rivers with poor hatches and less selective cutthroat trout. Because of the pattern’s visibility and good floatation in faster water, I often used the Thorax Dun as my point fly. From the bend of the hook, I attached related mayfly patterns like a CDC Parachute for a flush-floating adult or cripple, a Halfback for a shallow emerging nymph, or a Trigger Nymph for a deeper emerging nymph. Doing this allowed me to fish multiple stages of a mayfly hatch at once. I could trigger various fish that were feeding on different mayfly stages without having to retie on a new fly each time.

Pattern Usage Basis

Using Fish Swami’s statistical analysis tool once more, I am able to break down the fish catch numbers based on colors of the CDC Biot Thorax Dun that I used.

Number Caught    Pattern    Pattern Color   
10  CDC Biot Thorax Dun  Olive  
38  CDC Biot Thorax Dun  Pale Yellow  
8  CDC Biot Thorax Dun  Pink  
12  CDC Biot Thorax Dun  Yellow  

I focused on three different mayfly hatches in 2007: Pale Morning Duns (PMDs) throughout the summer and early fall, Pink Alberts in the early fall, and Blue-Winged Olives in the fall and early winter. Most of my success came with the pale yellow or yellow Thorax Duns, which is due to the longer duration PMD hatch I fished during the summer. To validate this statement, I can perform another query to determine how many fish I caught each month on the CDC Biot Thorax Dun.

Number Caught    Pattern    Month   
29  CDC Biot Thorax Dun  June  
14  CDC Biot Thorax Dun  July  
4  CDC Biot Thorax Dun  August  
16  CDC Biot Thorax Dun  September  
1  CDC Biot Thorax Dun  October  
4  CDC Biot Thorax Dun  November  

Indeed, 47 of the 68 fish caught on the Thorax Dun were caught during the summer months of June, July, and August, when PMDs are most prevalent.

Fish Species

I can also break down the number of fish caught on the CDC Biot Thorax Dun according to fish species.

Number Caught    Fish Species   
50  Brown Trout  
18  Rainbow Trout  

Normally selective brown trout found the Thorax Dun to be an effective mayfly adult imitation.

Time of Day

To show the power of Fish Swami’s statistical analysis tool, I have run several more queries. The following table shows me what time of day I caught fish using the CDC Biot Thorax Dun.

Number Caught    Time of Day   
68  2:52 PM to 9:11 PM  

It seems that I only used the pattern in the afternoon and evening, which corresponded to most of the mayfly hatches I fished during the summer.

I can also run a query to determine what the skies were like when I caught fish on the Thorax Dun:

Number Caught    Skies - Morning    Skies - Afternoon    Skies - Evening   
2  null  null  null  
9  null  null  Sunny  
21  null  Sunny  Sunny  
8  null  Mostly Cloudy  Cloudy  
10  null  Cloudy  Mostly Cloudy  
13  null  Cloudy  Cloudy  
1  Cloudy  Cloudy  Mostly Cloudy  
4  Cloudy  Cloudy  Cloudy  

The results of this query are a bit harder to understand initially. In summary, I caught 30 fish on the pattern when the day was Sunny and I caught 36 fish on the pattern when the day was cloudy. Interestingly, the numbers are pretty even for my sample set – the Thorax Dun worked well in both sunny and cloudy conditions.

Next, I can run a query to determine what wind conditions were like:

Number Caught    Wind - Morning    Wind - Afternoon    Wind - Evening   
2  null  null  null  
2  null  null  None  
3  null  null  None, Very Light - <5 knots  
4  null  null  None, Light - 5 to 10 knots  
10  null  None, Very Light - <5 knots  None  
3  null  Light - 5 to 10 knots  Very Light - <5 knots, Light - 5 to 10 knots  
13  null  Light - 5 to 10 knots, Medium - 10 to 15 knots  None, Very Light - <5 knots  
13  null  Light - 5 to 10 knots, Medium - 10 to 15 knots  Light - 5 to 10 knots  
3  null  Medium - 10 to 15 knots  Light - 5 to 10 knots  
2  null  Medium - 10 to 15 knots, Heavy - 15+ knots  Light - 5 to 10 knots  
8  null  Medium - 10 to 15 knots, Heavy - 15+ knots  Light - 5 to 10 knots, Medium - 10 to 15 knots  
1  None  None, Very Light - <5 knots  None  
3  Very Light - <5 knots  Very Light - <5 knots  Very Light - <5 knots  
1  Very Light - <5 knots  Light - 5 to 10 knots, Medium - 10 to 15 knots  Medium - 10 to 15 knots  

This query needs significant consolidation to glean out the important information. If I group the information into four categories based on overall wind activity for the day, I get:

None-Very Light: 23
Light or less: 3
Medium or less: 32
Heavy or less: 10

The pattern seemed to fish well in very light wind or medium wind. It’s harder to make a solid statement about this, since often on the days where the wind blew medium or heavy speeds, the wind was gusty and there were periods of calm where fish rose consistently to adults. This can be seen by the number of rows where both “Light” and “Medium” values were checked for wind speeds during the same day segment. It’s likely I caught more fish on the surface during the “light” periods versus the “medium” periods.

2007 Vs. 2006

It is interesting to compare my top 10 flies from 2007 with 2006:

Number Caught    Pattern    Number Caught    Pattern   
68  CDC Biot Thorax Dun  95  Pheasant Tail BH  
61  Zebra Midge  75  Gold Ribbed Hare's Ear  
50  Pheasant Tail BH  44  Gold Ribbed Hare's Ear BH  
49  Disco Zebra Midgeling  42  Foamy  
40  CDC Parachute  42  Stimulator  
35  Elk Hair Caddis  35  Pheasant Tail  
29  Halfback  27  Green Rockworm  
27  X-Caddis  21  Clear Wing Spinner  
26  Trigger Nymph (Mercer)  20  Copper John  
24  Parachute Midge Emerger  19  Elk Hair Caddis  

While 2007 was dominated with mayfly adult and midge larvae/pupae patterns, 2006 was the year of the nymph. The Pheasant Tail and Gold Ribbed Hare’s Ear patterns comprised 4 of my top 10 patterns. The Pheasant Tail alone contributed to 21% of my catch totals for 2006. It was a different story in 2007. The CDC Biot Thorax Dun only constituted 9% of my catch totals, and I caught double-digit numbers of fish on 22 different patterns.


The 2007 year was tremendous for me in being able to fish often and somewhat consistently throughout the months of the year. One major benefit of fishing the same waters throughout the course of a year is being able to watch how the seasons unfold, how hatches come and go, and how fish react to their environment. Documenting my outings in Fish Swami has helped me develop a more accurate feel for the varying conditions that affect angling success on my local waters. In time, my personal logs will tell a story of how I developed as an angler, and how I enjoyed the times I was able to spend outdoors. For now, I can at least use my fishing logs to count how many fish I caught on a CDC Biot Thorax Dun.

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