Chesapeake Cobia and Fly Design: What fly pattern works best?

I did not have a good year sight casting for cobia.  Over four days in July and August, I hunted these fish, armed with my 10 weight and a number of hand-tied flies.  I found small fish (24″-30″) on two of those days, and in those cases, I either could not get sighted fish to eat, or when they did eat, the hook pulled.  As with all things fishing, each new challenge only fuels my obsession, and the last few weeks of cold have left me studying scientific papers, examining my flies and tackle from last year, and thinking about factors that I may not have considered.

So what worked?  What didn’t work?  And why?

What did work, fly pattern-wise, was a 4″-5″ chartreuse and white half-and-half.  Fish ate this fly, and chased it down eagerly.  However, after hooking a few and having them spit the hook, and having to turn the boat engine on and off, the fish went deep, and fly action ended.

A half-and-half pattern that Virginia cobia actually liked.

What didn’t work, pattern-wise, were large menhaden patterns (7″ – 12″),  and fat/broad crab patterns (lightly weighted).  While the menhaden patterns did draw the occasional curious fish, it didn’t cause a strike.

Why?  Doing a little research this winter, I found an informative journal article authored by scientists at William and Mary College and the Virginia Institute of Marine Science.  The article presented data on cobia stomach contents in Chesapeake Bay, with the major take-away being that cobia in the Chesapeake primarily eat crab (~70% of stomach content volume), and that those crabs are either blue crabs or lady crabs in the 3″-5″ range.  Fish species like menhaden, mullet, and eel made up a very small portion of the sampled cobias’ stomach contents by comparison.

So as a fly fisherman, we should be throwing full crab patterns, right?  Not necessarily.  We need to throw flies in the same size range and that move like these crabs, but they don’t have to look exactly like a crab.  Crabs swim at a steady pace typically, but when attacked, they dive towards cover.  In a buoy situation, this means heading back towards the buoy chain, or straight to the bottom.  So by virtue of this, we need flies in the 3″-5″ range, preferably bushy and full of movement, and that have enough weight to dive when the angler pauses his retrieve.  In my experience with cobia, this is when 90% of eats will occur – the dive.  And it is also why jigs account for most cobia caught on conventional tackle.

Prototype crab-inspired half-and-half.  Brown rabbit strip instead of hackles, EP fibers to give it body and ease of casting, and tan and light blue bucktail to give it movement.  A few strands of gold/orange flashabou were added, but might not be necessary.

One final point:  I have a sneaking suspicion that cobia have an excellent sense of smell, and that their hesitance to eat a fly is often the result of the fly’s odor.  The flies that did get eats this summer were older, and had been in salt water often.  The flies that were refused had never been used, and featured head cement that smelled strongly (UV-light cured acrylic).  In the future, I will use cobia flies that are not treated with head cement, epoxy, or cured acrylic.  While this will result in a shorter life for the fly, it should mean more fish for the angler.

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