“Trophic level” is a measure of how far up the food chain an animal is. It’s generally used in ecological studies to show how much impact a predator has on its habitat – sharks have high trophic levels, because they eat lots of smaller fish. New Scientist is using trophic levels in a different way – to get ecological information out of our cookbooks:
Over the 122 years of the study, the average trophic level of the recipes rose from 2.92 to more than 3.4. In other words, newer recipes were more likely to call for the large, predatory fish than were older recipes.
Levin had expected the opposite trend, because decades of intense fishing have depleted the populations of many fish with a high trophic level, and as a result more and more of the world’s fish harvest is now made up of smaller “trash” fish of lower trophic levels. He suggests it didn’t work out that way because cookbooks don’t reflect what we eat so much as what we aspire to eat. “It’s more about culture than fish,” he says.
Indeed, Levin suspects that rarity may be partly responsible for the prestige of fish like cod and tuna. “When food is expensive, that’s the stuff that shows up in cookbooks,” he says. If so, cooks will continue to seek out these species even as their populations dwindle still further – a perverse demand that could stymie efforts to restore healthy fish populations.