Indicator Code: MTI
Objective: Ecosystem Vitality
Policy Category: Productive Natural Resources
Subcategory: Fisheries
Indicator Short Name: Marine Trophic Index
Indicator Full Name: Slope of Marine Trophic Index from 1950-2004
Indicator Description: The marine trophic level ranges from 1 in plants to 4 or 5 in larger predators. It expresses the relative position of fish and other animals in the hierarchical food chain that nourish them. They provide food for small fish which, have a trophic level of about 3,and the small fish are eaten by slightly larger fish that have a trophic level of 4, which, in turn, are what large predators such as sharks and marine mammal and humans typically eat (Pauly and MacLean 2003).
If the average level at which a country’s fisheries is catching fish declines over time, it means that the overall the trophic structure of the marine ecosystem is becoming depleted of larger fish higher up the food chain, and is resorting to smaller fish.
This indicator measures the slope of the trend line in the Marine Trophic Index (MTI) from 1950-2004. If the slope is 0 or is positive, the fishery is either stable or improving. If the slope is negative (below 0), it means the fishery is declining, and that smaller and smaller fish are being caught.
Units: Slope of Trend Line
Country Coverage: 134
Reference Year 1950-2004
Target: No Decline
Target Source: Expert Judgment
Short Source: Sea Around Us Project and the Convention on Biological Diversity
Source: Sea Around Us Project and the Convention on Biological Diversity
Source URL: http://www.seaaroundus.org/
Methodology: Using the Sea Around Us website, data were gathered on the slope of the trend line in the Marine Trophic Index (MTI) from 1950to 2004 for a country’s exclusive economic zones (EEZs). For countries with more than one EEZ, a weighted average slope was calculated on the basis of the relative size of the EEZs.
Data for Albania were only available through 1970 and data for Eritrea were only available through 1978.
Additional Citations: Pauly, D., and J.L. MacLean. (2003). In a Perfect Ocean: The State of Fisheries and Ecosystems in the North. Washington, DC, Island Press.
Pauly, D. and Watson, R. (2005). Background and interpretation of the ‘Marine Trophic Index’ as a measure of biodiversity. Philosophical Transactions of The Royal Society: Biological Sciences 360: 415-423.