Fish Populations are Reduced by 78 Percent in Hawaii Due to Human Impacts

Most people are aware that humans have a large impact on coral reefs. But what exactly is the extent of this impact? Scientists have taken a closer look and have discovered that we may have a larger influence than we thought.

In this latest study, the researchers studied nearly 40 islands and atolls across the central and western pacific, including 25 unpopulated islands. This allowed them to see the relative influence of environmental variation and human presence on reef fish.

The scientists accounted for environmental variation among reefs. The researchers also took data on oceanographic and human population at each reef location that they included and then combine this data in models to investigate the influence of both environmental and human variables on reef fish abundance.

 In the end, they discovered that human presence is associated with large reductions in reef fish biomass compared to projections for uninhabited islands and atolls. In fact, the scientists discovered that there was reductions of 20 to 78 percent at reefs in the Main Hawaiian islands, up to 69 percent depletion in the Mariana Archipelago and up to 56 percent depletion in American Samoa.

It appeared as if fish higher up in the food web, like group, were most susceptible to the influence of humans presence. The sharpest declines in fish abundance were associated with relative low human population densities, with continuing but more gradual fish declines seen on highly populous islands such as Oahu and Guam.

"The association between oceanic productivity and fish biomass that we document for Pacific reefs is an important reminder that not all coral reefs have the same capacity to sustain high fish biomass," said Kate Hanson, co-author of the new study, in a news release. "There is natural variability among reefs that is unrelated to their history of human influence."

The findings are published in the journal PLOS One.

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