The article establishes the importance of the mean trophic level of fisheries as a tool for measuring the health of ocean ecosystems.

Scientists tracked tiger sharks at the top of the food web and collected data on their feeding behaviour, what they ate and how much.

Likewise, they collected feeding data on the other organisms in the food chains down to the primary producers, such as algae.

Such models allow scientists to compute the complex effects that occur, both direct and indirect, from the interactions of the many ecosystem components.

This "fishing down the food web", said Pauly, would in time reduce people to a diet of "jellyfish and plankton soup".

[15] The response of Pauly's team was published in the same paper, claiming that the corrections suggested by the FAO, such as accounting for aquaculture, actually made the trend worse.

[19][20] A study on Alaskan marine fisheries concluded that in the examined area, the decline of mean catch trophic level was connected to climate-driven fluctuations in biomass of low trophic level species rather than predator collapses, and suggested that similar dynamics might be in play in other instances of reported food web degradation.

[21] In 2000, the Convention on Biological Diversity, an international treaty aimed at sustaining biodiversity which has been adopted by 193 member countries, selected the mean trophic level of fisheries catch as one of eight indicators for immediate testing.

The index is also a proxy measure for overfishing and an indication of how abundant and rich the large, high trophic level fish are.

[24] Changes in the Marine Trophic Index over time can function as an indicator of the sustainability of a country’s fish resources.

Wild stocks of bluefin are now threatened, and the fisheries scientist Konstantinos Stergiou and colleagues argue that the "fact that the capacity of tuna farms greatly exceeds the total allowable catch indicates lack of conservation planning in development of the tuna-fattening industry, which, ideally, should have been linked to fisheries management policies, and may lead to illegal fishing".

This feed consists of fishmeal processed from forage fishes like sardines and anchovies that humans would otherwise consume directly.