While the strength of a steelhead "strain" may be attributed to the obstacles it must overcome in its journey (like the Thompson steelhead's journey through Hells Gate, or the Dean River's lower canyon), the one obvious factor affecting fish size is the distance the fish travels in the ocean (and the time it spends out there). The fact is that steelhead have the greatest number of variants in life cycle of any andromous species, from time spent in the ocean, distance traveled, time spent in the freshwater pre spawn and post hatch. Thompson fish probably spend 3-4 years in the rich waters off Alaska's Aleutian Islands, and many return for a 2nd or even third season. A particularly hardy BC female was determined, though scale analysis, to have returned for a 6th time, (although the statistical return for a 2nd visit is only about 10%). Smaller strains, on the other hand, likely spend their time closer to their natal streams and may return after only 1-2 years in the ocean (like many California and Oregon steelhead that average 5-10 pounds), and many many not return for a 2nd or third visit. This longer time spent at at sea is why you see 20+ size fish in the Thompson, but the journey through the Hells Gate may be why they fight harder than a 20 pound fish in the Indian River did. The smaller Oregon strains, likewise, may be every bit as strong as a 10 -14 pound Vedder steelhead if they have to negotiate a steep canyon gorge or travel hundreds of kilometers inland like the Thompson fish do. Another factor may be the timing of the run. The Thompson fish is a "Summer run" fish (they enter the Fraser in August) and so they are stronger and more aggressive than true winter run fish like the Vedder steelhead that get more lethargic as the temperatures drop. This is similar to how the Dean steelhead (considered by many to be the strongest "strain" around) fight harder than the Skeena tributary fish in the Bulkley or Morris systems (even though they are both summer runs). The Dean fish are targeted when they enter in the summer, while the Bulkey and Morris fish are targeted , like the Thompson fish, in the fall (even though they entered the Skeena at the same time the Dean fish entered the lower Dean River. Since the water in the fall is cooler, their metabolism is slowed, and the Bulkey and Morris fish have also used up more of their stored energy in their 300km journey up the Skeena. While still summer run "players," these fish are not considered as strong as the Dean fish, which are fresh from the ocean and swimming in warmer summer waters, a recipe for aggressive strong fish. Now imagine if you were to be lucky enough to hook into a 20 pound early Thompson fish in September. That would be a fight to remember. The 12 pound summer run Steelhead I hooked in August in the Seymour estuary while fishing Pinks was the best fight I have ever had, 10 times better than a similar sized fish I caught in the lower Vedder/Sumas on New Years Day.