Atlantic salmon and sea trout from Guernsey’s west coast

June 13th, 2011 by Richard Lord

Two salmonids turn up in Guernsey waters.  These species can be confused because of their similar appearance.

During high tide at 3 pm on 11 June 2011 an Atlantic salmon, Salmo salar, was caught near Fort Hommet on Guernsey’s west coast.  The salmon was captured using a live sand eel as bait.  The salmon weighed 1490 grams and had a total length of 67.2 cm and a standard length of 56.6 cm.  For its length it was thin and undernourished.

Atlantic salmon, Salmo salar, landed off Fort Hommet, on Guernsey's west coast at 3 pm on 11 June 2011 (click image to expand - ©RLLord)

According to Guernsey angling expert Len Le Page, anglers catch on average one Atlantic salmon in Bailiwick waters each year.

This fish had the appearance of an escaped farmed fish although this is conjecture on my part.

Declan Quigley who researches and writes about fish thinks it looks more like a kelt – a female salmon that has reproduced in a river system and returned to sea.  Only a small percentage of Atlantic salmon manage to do this as the mortality rate after spawning is high.

On the night of 11 June commercial fisherman Nick Vining caught a sea trout, Salmo trutta, in Vazon Bay, which is immediately south of Fort Hommet.  The sea trout is a brown trout that migrates to sea to spend its adult life.

The sea trout caught by Nick Vining in Vazon Bay on the night of 11 June had a total length of 40.1 cm (click image to expand - ©Nick Vining)

The sea trout had a total length of 40.1 cm although it couldn’t be weighed because it had been filleted for dinner.

Atlantic salmon and sea trout can be identified by their teeth, the number of gill rakers on the first gill arch, the colour of the adipose fin, and the size and arrangement of spots on the body below the lateral line.

Atlantic salmon have 17 to 24 gill rakers on the first gill arch.

The Fort Hommet salmon had a total of 21 gill rakers.   Twelve gill rakers were on the lower limb of the first gill arch and 9 were on the upper limb.

Sea trout have 13 to 18 gill rakers on the first gill arch.

The Vazon individual had 17 gill rakers in total.  (Ten on the lower limb and seven on the upper limb.)

The arrangement of teeth in the roof of the mouth can also be used to separate the two species.

Both species have a line of teeth down the middle of the roof of the mouth.  These teeth belong to the vomer.

The mouth of the sea trout showing the vomer and palatine teeth in the roof of the mouth (click image to expand - ©RLLord)

In sea trout the anterior end of the vomer has two to six teeth.

There are no teeth on the head of the vomer in Atlantic salmon.

The salmon from Fort Hommet had no hard teeth on the vomer.  The sea trout’s vomer teeth were stout and sharp.

Salmonids have a fleshy fin called the adipose fin behind the dorsal fin.  Sea trout have a yellow and orange edge to their adipose fin.

The adipose fin of the sea trout, Salmo trutta, has a distinct orange edge even after several days in the refrigerator (click image to expand - ©RLLord)

Atlantic salmon have a grey adipose fin.

Sea trout have numerous dark spots above and below the lateral line.  Atlantic salmon have smaller black flecks on their flank, which are not usually found below the lateral line.

Another character that is often used to separate the two closely related species is the length of the maxilla bone forming the margin of the top jaw.  In Atlantic salmon this bone reaches to the hind margin of the eye but not beyond it.

The sea trout maxilla bone extends beyond the hind margin of the eye.  This character is more noticeable when the fish’s mouth is closed.

The head of Nick Vining's sea trout showing the maxilla bone below the eye (click image to expand - ©RLLord)

 

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