Hi Michaelt,
good question, it was once thought that they were all the same. However, with more research, there's more features which distinguishes the two. There are a few morphological differences (some are very slight) as well as DNA differences differentiating the two different species; dolly varden (Salvelinus malma) and bull trout (Salvelinus confluentus).
A good book to look though is the new one that Dr. JD McPhail just published called "Freshwater fishes of British Columbia". This book is great as it tells you not only unique characteristics, but it's distribution in BC of each species.
As a fisherman, I often look at the size as well as the upper Maxillary as bull trout are often a larger and have longer upper Maxillary than dollies. The upper Maxillary of a bull trout will often go beyond the eye. In the below picture you can sort of see how far back the upper Maxillary passes beyond the eye regardless of the size of the fish. Typically bull trout are more piscivorous than dollies as suggested by the size of mouth and larger teeth, however, dollies are known to also eat fish.
Also, depending on the watersheds, you'd find more dollies than bulls and vise versa. Yes, dollies are more coastal and bull trout are more interior, however, there are some exceptions as there is a large overlap in distribution e.g. Fraser and a few other watersheds, so you can find them living in the same water systems. For example, the Fraser river, Skagit, Squamish, to name a few has both species.
You can find both species in lakes, as well as rivers and streams. It's true that there are land locked populations, but there are also many that are connected to the sea. I hope that helps.
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Topic: Bull trout and dolly varden differences (Read 10257 times)