Science Advisory Report 2009/074
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 240,000 to 366,000 between 1996 and 2006. Catches have been significantly reduced since 2007 with a reported catch of 72,400 in 2009. Greenland catches have increased steadily since the mid 1970’s reaching a peak of approximately 100,000 in 2000. Since then they have fluctuated, averaging around 85,000. Catches in the Canadian Arctic remain low (<1,000).
- This assessment relies on pup surveys completed once every four - five years combined with estimates of reproductive rates and removals to determine total abundance using a population model.
- Total removals of harp seals were estimated using reported catches, estimates of bycatch 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 2004, high catches in Canada and Greenland resulted in average annual removals of 465,500. However total removals have declined to 250,000 in 2009, primarily due to the lower catches in the Canadian commercial hunt.
- Pregnancy rates among 4 year olds are low and without trend while pregnancy rates of 5 and 6 year olds increased during the 1970s, but declined by the mid 1980s. Pregnancy rates of seals 7 years of age and older remained high until the mid 1980s when they declined to their current low levels. The most recent pregnancy rates, which include data from 2002-2007, are lower than those used in 2008 to estimate total population size of Northwest Atlantic harp seals.
- Surveys were carried out in March 2008 to estimate current pup production. A total of 287,000 (SE=27,600 CV 9.6%) pups were born in the Southern Gulf, 176,800 (SE=22,800, CV=12.9%) in the northern Gulf and 23,400 (SE=5,500, CV=23.5%) in a small concentration at the Front. Visual and photographic surveys of the main concentration at the Front yielded significantly different estimates of 589,400 (SE=49,500, CV=8.4%) and 1,161,600 (SE=112,300, CV=9.7%) pups, respectively. Possible causes for the difference have been examined, but no explanation has been found.
- Using the photographic survey of the large Front concentration resulted in an estimate of total pup production in 2008 of 1,648,800 (SE=118,000, CV=7.2%), whereas using the visual survey resulted in an estimate of 1,076,600 (SE=61,300, CV=5.7%). The lower estimate is consistent with that predicted by the harp seal assessment population model but the higher estimate is not.
- Given the discrepancy between the above estimates of pup production, the population model was fitted to the lower pup production estimate in 2008 resulting in a total population of 6.5 million (95% CI= 5.7 to 7.3 million) in 2008 and 6.9 million (95% CI=6.0 to 7.7 million) seals in 2009. The 2008 number is higher than the population projection from the last assessment due, primarily, to the lower reproductive rates observed in recent years and fitting to the new pup production estimate.
- Changes in the population assessment model resulted in a slightly increased estimate of total population (~4%). However, the new estimate was more precise (i.e. lower variance).
- The three harvest scenarios proposed by Fisheries and Aquaculture Management, including one with annual catches of 300,000 in 2010-2012, will respect the objectives of the harp seals management plan and would not result in the projected population dropping below N70 before 2012.
- Uncertainty about the estimate of pup production at the Front in 2008, the variability associated with model parameters, as well as potential changes in natural mortality rates due to environmental conditions add uncertainty to estimates of population size and the effect of harvests on the trajectory of the population. Additional uncertainty is associated with our lack of knowledge about removals in Greenland. Because surveys are only completed once every four - five years and only count pups, changes in natural mortality rates of YOY in intervening years may not be detected during subsequent assessments until 10 to 15 years later. The effects of changes in adult mortality would likely be detected earlier.
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