Conservationists have started marketing a five-year rhino bond, which bankers say will be the world’s first financial instrument dedicated to protecting a species.

Investors in the $50m bond will be paid back their capital and a coupon if African black rhino populations in five sites across Kenya and South Africa increase over five years. The yield will vary depending on changes in the rhino population, which has fallen rapidly since the 1970s.

The bond is likely to have different categories of investment, with some investors taking a “first loss” position. If rhino numbers drop, those investors will lose their money depending on the scale of the decline and the terms of their investment, while investors in other categories will be repaid.