Research Document - 2005/090
Abundance of Northwest Atlantic harp seals (1960 – 2005)
By Hammill, M.O., G. Stenson
Abstract
The Canadian and Greenland hunt for Northwest Atlantic harp seals is the largest marine mammal harvest in the world. Therefore, it is important to monitor abundance and population trends to ensure that these removals are sustainable. Since 1980 abundance has been estimated using a two-parameter population model that estimates unreported mortality (i.e., natural mortality plus unreported hunting mortality) and an initial abundance to fit to independent field estimates of pup production using data on removals and age specific reproductive rates.
A population model incorporating pup production estimates since the late 1970s, reproductive rates since 1960 and human induced mortality (catches, by-catch in fishing gear and struck and lost) since 1952 was used to estimate total abundance for the period 1960 - 2004. The harp seal population declined during the 1960s to a low of less than 2 million in the early 1970s, and then increased steadily to 1996. Since then the population has remained relatively stable at the highest values in the time series, and possibly its highest level since commercial exploitation began in the 1700s. The estimated total population size in 2005 is 5.82 million (95% CI= 4.1-7.6 million).
The current Canadian landed sustainable yield is estimated to be 250,000. Owing to the increasing uncertainty associated with future population changes, there is a 20% chance that the population will decline to N70 by 2013 under the current sustainable harvest. Harvests greater than 300,000 would result in the likelihood of the population reaching N70 prior to the end of a 5 year management plan being greater than 20%.
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