I often use eulachon (Thaleichthys pacificus, a small, anadramous smelt) as an example of “archaeologically-invisible” food. They are also known as “candlefish”, on account of being so oily that a wick jammed down their throat will burn like a candle.
These small fish run by the millions up rivers to spawn, where they could be intercepted. Traditionally, many or most eulachon would be processed into eulachon oil, or grease: a highly nutritious, calorie-dense substance that preserved very well and could also be used to preserve other foods such as berries. The means of processing was to put them into a large container, perhaps an old canoe, known colloquially as a “stink box”, let them “rest” there for a week, and then heat them up, enabling the oil to rise and then be skimmed off, or pressed out. The residue (bones, guts, brains, etc.) would then be returned to the river and few or no bones would make it away from the processing site. In this way, eulachon provided a staple food, a nutritional supplement, a means of preservation, and an extremely valuable trade item – when Alexander Mackenzie arrived near Bella Coola in 1793, “Over Land, From Canada”, he did so on one of the well-worn grease trails that linked coast to interior. Since the fish arrive in the early Spring, they were hailed as starvation busters in lean years. Nonetheless, archaeologically they are almost invisible, relative to their importance.
It is therefore sobering to read that U.S. President Obama has listed the Columbia River eulachon as an endangered species: eulachon are becoming almost invisible relative to the real world now, it seems.