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Between 1970 and 1999, the Marine Species Population
Index recorded a decline of about 35%.

The Marine Species Population Index provides an assessment of the
average change over time in the populations of 217 species of marine
mammals, birds, reptiles, and fish. The index represents the average
value of six regional ocean indices. More pronounced declines are
seen in the southern oceans, which is attributed to the fact that
major losses and degradation of marine ecosystems in the industrialised
world took place prior to 1970.
Marine species are generally more difficult to monitor than terrestrial
ones. Assessments are therefore based primarily on fishery catches,
and the monitoring of land breeding species (e.g. turtles, birds
and seals). However, these species are over-represented in the index,
which should have a far greater proportion of invertebrate species.
Source: Loh, 2000.
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