It turns out trickle-down economics don’t work any better for people than for fish. While the communities that surround coral reefs get richer, the fish lose out.

A study by the Wildlife Conservation Society (WCS) and other organizations found that the health of coral reef fish is directly linked to local economies. The researchers examined reef systems, human population densities, and socio-economics along Africa’s Indian Ocean coast, and drew a surprising correlation between the region’s middle class communities and low fish levels. Curiously, the fish in both the poorer and the wealthier areas fared better.

“This is a significant finding on how socio-economics can influence reef fisheries in surprising ways,” said Dr. Tim McClanahan, WCS coral researcher. “It also shows the importance of combining ecology with social science for conservation planning on a regional scale.”

The explanation lies in the interplay between traditional customs and economic growth. In poor communities, many of which rely heavily on marine resources, fishermen use traditional, low-tech fishing methods. When a community becomes wealthier, it tends to use more motorized fishing vessels and fishing gear such as handlines, even if it relies less on fishing for subsistence. The more sophisticated fishing techniques tend to be much more destructive on marine environments. Economic growth during the early stages can also erode a community’s cultural restrictions on overfishing. Among the countries studied, Kenya, in particular, has experienced a sharp decline in cultural restraints that had kept fishing levels in check.

The most affluent communities, by contrast, are less dependent on marine resources, with more salaried positions and diverse economic opportunities. Wealthier communities possess higher levels of technology—larger boats that enable fishermen to fish on the open sea—and are more aware of the importance of coral reefs on ecological health.

Predictably, the research also found that high human population density had a consistently negative—though not strong—effect on fish levels. And protected marine sites with no fishing had three times more fish than sites where fishing was permitted.

McClanahan emphasized that coral reef fishery management depends not just on fishing laws but also in part on a community’s access to wider economic opportunities, as well as infrastructure developments like schools and hospitals. Governments, donors, and other agencies can help communities invest in these programs and livelihoods, he said.