Today we were on the Diebidale surveying below the dam, and later on the Gruinards burn for the Scottish Government’s sampling programme. As we primarily electrofish for salmonids, I thought it would be nice to share a quick guide to how we ID the two species at juvenile stage.
1. In trout the jaw extends further back than in salmon, past the pupil in of the eye. In salmon however, the jaw is smaller and usually only extends to the mid-point of the pupil.
2. Salmon have larger pectoral fins than trout. Usually they will extend further than the start of the dorsal fin, whereas in trout the pectoral fin will not extend past the dorsal. This is an adaptation to the slightly different niches that they occupy. Salmon are more commonly found in faster flowing water, and larger pectoral fins assist with holding themselves in the current.
3. The wrist of the tail in salmon is thinner than in trout.
4. Salmon have a much more pronounced fork in their tails than trout.
There are other signs that people use, such as the parr marks in salmon are more pronounced, adipose fin of trout being bright orange (I’ve seen a few salmon with this feature too though) and the number of spots on the gill cover (salmon have less than trout) and in general salmon have a more streamlined body than trout. The 4 numbered features are what I tend to use when out in the field however.
7th August 2018