A method to estimate pre-exploitation population size.

Area of Science:

• Ecology
• Conservation Biology
• Historical Ecology

Background:

• Antarctic fur seals (Arctocephalus gazella) on South Georgia faced near extinction due to over 100 years of commercial exploitation.
• Rebounding populations are now sometimes viewed as a nuisance, necessitating an understanding of their historical abundance to avoid shifting baseline syndrome.

Purpose of the Study:

• To estimate the pre-exploitation abundance of Antarctic fur seals on South Georgia.
• To provide historical context for current population assessments and conservation targets.
• To inform efforts for developing a green list of recovering species.

Main Methods:

• Reconstructed the fur seal harvest from 1786 to 1908 using ship logbooks and historical records.
• Interpolated missing harvest data using a generalized linear model.
• Employed an approximate Bayesian computation framework and a stochastic age-structured population model.

Main Results:

• Estimated the pre-exploitation abundance of Antarctic fur seals on South Georgia at 2.5 million females (95% CI 1.5-3.5 million).
• This estimate suggests current population levels may be comparable to pre-exploitation conditions.
• Highlights the ecological consequences of current fur seal numbers on the island.

Conclusions:

• Understanding historical population baselines is essential for defining species recovery and setting appropriate conservation targets.
• Archival records are vital for reconstructing past ecological states and informing present-day conservation.
• Current Antarctic fur seal populations may reflect a return to pre-exploitation ecological conditions.