Lecture 13 Reading: Amsterdam albatross PVA Modeling

"Risks of decline and extinction of the endangered Amsterdam albatross and the projected impact of long-line fisheries"
Pablo Inchausti and Henri Weimerskirch (2001)


The Amsterdam albatross is one of the rarest bird species in the world, with only a single population in Amsterdam Island (SE Indian Ocean). These birds have the following characteristics: large bodies, long life spans (30-40 years on average), low fecundity, and very high annual adult survival. The Amsterdam albatross is considered an endangered species. The proposed possible explanations of the bird’s rarity include the degradation of the island and impact of the long-lining fisheries in southern Indian Ocean in the 1960s and 1970s. However, because the land conditions has been improving, long-line fisheries is considered the most threatening factor.

Stochastic demographic models (Population Viability Analysis (PVA) models) provide a systematic way to assess possible factors placing a species at risk of extinction. (However, PVA models require a lot of age specific data, which are usually unavailable for endangered species.) This paper uses PVA models to quantify the decline of the Amsterdam albatross and their risk of extinction. The paper also makes an estimation of the potential impact of re-establishment of long-line fisheries on the Amsterdam albatross population. The model looks at estimated age-specific fecundity and survival data using “no fisheries” as a baseline scenario (no fisheries effects and no measurement errors) against the predicted effects of fishery.

The results show that the Amsterdam albatross is unlikely to face a major decline in population in the next 50 years (unless there are major catastrophes). The study also shows that for small populations, it is difficult to assess with certainty the risk of extinction, even when long-term data is available. A two-fold approach – long-term monitoring combined with modeling – is suggested, to avoid any potential risks of population decline for the species.
