Regarding the scars on Sockeye salmon ~ I used to work on a commercial troller (MANY years ago) and noticed a surprisingly high number of lateral scars on sockeye but not on other salmon species. I did a little investigating and found that the high frequency of lateral slash marks on the sides of high-seas salmon is caused by the attack of
daggertooth. A deep sea predator of sockeye salmon that grows to almost 5 feet long. They don't make them much meaner than this guy. [}
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Dissection of freshly eaten prey suggests that the North Pacific daggertooth Anotopterus nikparini sever the spine of small prey with a single slashing blow. The bite marks indicate that the immobilized prey is manipulated and swallowed head first. Frequent evidence suggests daggertooth wound prey which are too large to consume whole by cutting off strips of flesh. In either case the wounds consist of a single prominent slash mark on one side and a series of inconspicuous marks on the opposite side. Retinal morphology provides supporting evidence that daggertooths are visual ambush predators that attack prey from below, and should be considered as epipelagic rather than mesopelagic fish. Visual acuity appears to be high, suggesting that frequent attacks on prey too large to be killed immediately is not error, but a well-defined feeding behaviour. The daggertooth may be a significant source of mortality for economically important fish such as all sizes of salmon.
REFERENCE: . W. Welch, P. M. Pankhurst, Visual morphology and feeding behaviour of the daggertooth, 2001, Journal of Fish Biology, Vol 58, Issue 5, pp 1427-1437
A little more info…..Daggertooth is a species that has been recently noticed as a predator of offshore salmon (Welch et al. 1991; Radchenko and Semenchenko 1996). Current Russian surface trawl surveys indicate that the abundance of daggertooth is not low in the western North Pacific and that it feeds on large numbers of salmon (Melnikov 1997). Slash marks from daggertooths are not frequently but sometimes found on salmon from high seas and coastal waters. The incidence of slash marks on salmon is usually low, ranging from less than 1% to 4 or 5%, in offshore waters (Ishida et al. 1991) but slightly higher (up to 12%) in coastal waters (Gilhousen 1989; Henderson et al. 1990). The species is widely distributed in offshore waters of the North Pacific Ocean (Nagasawa 1992), and its abundance seems to have been increasing since the early 1990’s. Based on this information, we can regard daggertooth as significant salmon predators as well as the salmon shark. Recent studies indicate that increases in salmon shark abundance in the whole region of the North Pacific has increased mortality of salmon during the high-seas phase of the life history.
