MARINE SPECIES level 2, then species such as cod and tuna are at around trophic level 4. The biomass of these high trophic-level fishes is estimated to have declined by two-thirds in the North Atlantic between 1950 and 2000. As the top predators have been systematically reduced in number, so the species around trophic level 3 have increased in abundance. To compensate for declining catches of high trophic-level fishes such as cod (Figure 13), species occupying lower trophic levels have been targeted. Not only has the cod catch declined, but the average size of cod caught has also shrunk. As smaller, younger cod tend to feed lower down the food chain than fully mature fish, this adds to the fishing down the food web effect. Figure 14 shows that the mean trophic level of fish catches in the Northwest and Western Central Atlantic fell from 3.3 in
The marine species index indicates that populations of 267 species of marine mammal, bird, reptile, and fish declined by about 30 per cent between 1970 and 2000. Figure 12 shows average trends in the populations of 117 Atlantic and Arctic Ocean species, 105 Pacific Ocean species, 15 Indian Ocean species, and 30 Southern Ocean species. The relatively stable trends in abundance of species in the Pacific and in the Atlantic and Arctic Oceans hide an effect known as “fishing down the food web”. Commercial fish species preferred for human consumption, such as cod and tuna, are generally high up in the food chain. If plants such as phytoplankton and other primary producers are assigned to trophic level 1, and zooplankton and other animals that feed on them are assigned to trophic
Fig. 12: MARINE SPECIES POPULATION INDEX, 1970–2000
1970 to 2.9 in 1994, a decline of about 12 per cent. In the Northeast Atlantic the mean trophic level of catches declined from about 3.5 to 3.4 over the same period. The decline of stocks of high trophic-level species is a direct consequence of overfishing, supported by subsidies which, in the North Atlantic, amount to about US$2.5 billion per year. The map shows the location of both warm and cold water corals, and examples of trends in selected marine species populations and their approximate locations around the world. The graphs do not necessarily indicate trends for the global population of each species, but may reflect trends in a local or regional population.
Fig. 13: ATLANTIC COD LANDINGS 1970–2000
1.4
3.6
3.5
Figure 12: The marine species index declined by about 30 per cent from 1970 to 2000. Indian and Southern Ocean species declined overall, while average trends in Atlantic and Arctic species and in Pacific species remained stable. Figure 13: Landings of Atlantic cod (Gadus morhua) declined 70 per cent between 1970 and 2000 (FAO 2004b). Figure 14: The average trophic level of fish catches in the Northwest and Western Central Atlantic declined by about 12 per cent and in the Northeast Atlantic by about 3 per cent between 1970 and 1994 (Pauly et al. 1998).
Fig. 14: MEAN TROPHIC LEVEL OF ATLANTIC FISHERIES LANDINGS, 1970–1994
Pacific Ocean 1.2
MARINE INDEX
0.8 0.6
Southern Ocean
0.4
Indian Ocean/ Southeast Asia
0.2
1970
1975
1980
1985
8 LIVING PLANET REPORT 2004
1990
1995
2.5
Mean trophic level
Million tonnes per year
Index (1970=1.0)
3.4
Atlantic and Arctic Oceans
1.0
0
Northeast Atlantic
3.0
2.0 1.5 1.0
3.2
Northwest and Western Central Atlantic 3.0
0.5
2000
0
2.8 1970
1975
1980
1985
1990
1995
2000
1970
1975
1980
1985
1990
1995