Research Document - 2011/100

Historical Abundance of Northwest Atlantic harp seals (Pagophilus groenlandicus): influence of harvesting and climate

By M.O. Hammill, G.B. Stenson, and M.C.S. Kingsley

Abstract

Reconstructing historical population size provides useful information for management and conservation by providing an indication of abundance prior to exploitation. When combined with environmental variables, such estimates can also provide insights into how a species may respond to climate change. The harp seal (Pagophilus groenlandicus) is an obligate pack-ice breeder and is arguably the most abundant phocid species in the north Atlantic. Reproductive rates and morphometric data indicate that density-dependent factors are affecting the dynamics of this population although the mechanisms are not clear. Harp seals have been commercially exploited since the early 1700s, although significant catches did not begin until early in the 19^th century. Catch data from historical records and recent harvests were incorporated into a surplus production model to reconstruct the dynamics of this population back to the late 18^th Century. The initial population was estimated at 11 million (SE=2,000,000) animals. Assuming that the population at that time was stable and at its environmental carrying capacity. This population estimate serves as a proxy for  current carrying capacity assuming that environmental conditions in the 18^th century were similar to conditions today.

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