The Marine Trophic Index (MTI) is a measure of the average trophic level (TL) of fish taken in a given year and is an indicator of the status of a marine ecosystem. Higher-TL species like cod and tuna are typically the more sought-after fish. A catch that contains mostly lower-TL fish suggests that higher-TL fish populations are depleted. To determine the MTI, one identifies the trophic level of all fish taken (how many at TL2, TL3, and so on) and then calculates the average TL represented by all fish taken that year.

One of the obstacles to the recovery of cod and other large predatory fish is the loss of their own prey. When cod are depleted, fishers pursue the herring, crabs, and shrimp at lower trophic levels, reducing the food supply for the cod and ultimately jeopardizing cod recovery.