Okay, so the recent sonar image from Jacobite Cruises was five years old. I updated the article to reflect that shortly after, but it seems the real image has been published in what was deemed a cock up. Original article here.
The image was taken off Urquhart Bay on the 27th April 2014. A zoom in of the screen grab is somewhat indistinct, but it seems to be showing a target hit at about 30 feet down which has a crescent shape that is reminiscent of the crescent shape we see for smaller fish all the time. Note that in the case of fish such as charr or salmon, it is the swim bladder that registers the strongest echo. The crescent shape is caused by the relative motion of the fish to the sonar.
This sonar image is not a small fish. What it is on an initial inspection is difficult to say and I have seen various strange sonar hits from nearly all the cruise companies now. The normal answer from them is to say it is anomalous and I guess that is where I will have to leave it myself!