Science Advisory Report 2011/070
Current Status of Northwest Atlantic Harp Seals, (Pagophilus groenlandicus)
- Northwest Atlantic harp seals are harvested in Canadian and Greenland waters. After averaging approximately 52,000 seals per year between 1983 and 1995, reported Canadian catches increased significantly to a range of 226,000 to 366,000 between 1996 and 2006. Canadian catches have declined significantly since 2007 with a reported catch of 40,370 in 2011. Greenland catches have increased steadily since the mid 1970’s reaching a peak of approximately 100,000 in 2000, but have declined to about 80,000 since then. Catches in the Canadian Arctic remain low (<1,000).
- Total removals of harp seals were estimated using reported catches, estimates of bycatch, primarily in the Newfoundland lumpfish fishery, and estimates of seals killed but not recovered (referred to as ‘struck and lost’) during harvesting in the different regions. From 1996 to 2006, high catches in Canada and Greenland resulted in average annual removals of 483,000. However total removals have declined to less than 250,000 in the past three years, primarily due to the lower catches in the Canadian commercial hunt.
- Catch information dating back to the 18th Century are available for this population. Incorporating these data into a population model results in an estimated pristine population in the early 1800s of about 11 million animals, with wide confidence limits. Assuming environmental conditions are similar today, this provides guidance as to what carrying capacity might be.
- Annual pregnancy rates have been estimated since the 1950s. Estimated pregnancy rates among 4 year olds are low. Estimated pregnancy rates of 5 and 6 year olds increased during the 1970s to a high of 55% and 84%, respectively, and then declined to around 10% for both ages. Pregnancy rates of seals 7 years of age and older remained high until the mid 1980s, but have since declined and become highly variable. In 2011, pregnancy rates of 7+ females were less than 30%.
- The last surveys of the Northwest Atlantic harp seal population were flown in 2008. Combining the estimates from the two photographic surveys at the Front (1,142,985, SE=104,284) with estimates of pup production in the southern Gulf (287,033, SE=27,561), the northern Gulf (172,482, SE=22,287) and another small group at the Front (23,381, SE = 5,492), resulted in a 2008 total pup production estimate of 1,630,300 (SE=110,400, CV=6.8%).
- A model assuming density-dependent population growth, carrying capacity of 12 million and annual reproductive rate data was fitted to the survey data. The model estimated a total population of 8,300,000 (95% CI=7,500,000-8,900,000) in 2008.
- The projected trend in the population between 2008 and 2012 is difficult to predict because of uncertainty associated with reproductive rates and how density dependence is expressed in the model. The 2010 assessment assumed that reproductive rates would remain high and predicted a 2010 population that would lie between 8.61- 9.55 million (95% CI 7.80 to 10.80 million) animals. However, reproductive rates have declined since 2008, and the estimated 2012 population is now estimated to be 7,700,000 (95% CI=6,900,000-8,400,000)
- Science was requested to examine a variety of harvest scenarios to determine their impacts on the population. Harvest levels that will continue to respect the objectives of the management plan will vary depending on the proportion of young of year (YOY) in the catch; annual harvests of 300,000, 250,000 and 150,000 animals will respect the management objectives if YOY comprise 97%, 90% and 70% of the catch respectively.
- Traditionally, 70% of the harvest has been allocated to the Front and 30% to the Gulf, based upon the relative sizes of the respective populations. Transferring up to 20% of the quota from one component to the other will not result in long-term conservation concerns if it is offset in subsequent years by an equal reduction in the allocation, so that over the term of the management plan, the number of animals removed from each herd does not exceed the total allocation for each component.
- These harvest recommendations are sensitive to the frequency of surveys, assumptions concerning carrying capacity and future changes in reproductive rates, ice conditions and harvests in the unregulated Greenland hunt.
- The current population is estimated to have declined slightly since 2008, nevertheless it is near its highest level since the mid-19th Century. It is recommended that sampling for reproductive samples be increased, particularly in the year of a survey and that the frequency of the pup production surveys be increased to every three years.
This Science Advisory Report has resulted from a Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, National Advisory Meeting of October 17-21, 2011 on National Marine Mammal Peer Review Committee Meeting (NMMPRC). Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.
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