Science Advisory Report 2020/020
2019 Status of Northwest Atlantic Harp Seals, Pagophilus groenlandicus
- Northwest Atlantic Harp Seals are harvested in Canadian and Greenland waters. Annual Canadian catches averaged 272,600 between 1996 and 2006. Since then catches have declined, averaging 63,000 between 2009 and 2019. Greenland catches reached a maximum of 100,000 in 2000, but currently average about 60,000 seals annually.
- The Newfoundland Lumpfish fishery is the primary source of bycatch mortality for Harp Seals in Canadian commercial fisheries. Estimated bycatch increased from less than 1,000 in the early 1970s to a peak of 46,400 in 1994, declining to approximately 5,000 by 2003. Lumpfish landings have continued to decline and a bycatch of Harp Seals was estimated to be 555 in 2018. Low numbers of Harp Seals are also caught in U.S. fisheries.
- Over the last decade, the estimated pregnancy rates of mature females have been variable, ranging from 0.2 in 2011 to 0.88 in 2015, due to changes in abundance and the environment. Reproductive rates have remained relatively high in the past five years.
- Harp Seals require stable ice for pupping, nursing and resting. The annual extent of ice cover in Atlantic Canada varies considerably, but overall has declined over the last 44 years, particularly in the Gulf of St. Lawrence (Gulf). Mortality of Young of the Year (YOY) caused by poor ice conditions has been incorporated into the assessment. If the ice cover continues to decline, the fraction of the population breeding in the Gulf is also expected to decline and may result in a permanent redistribution of the breeding population.
- Photographic and visual aerial surveys were flown between March 6 and 18, 2017. The timing of births in the southern Gulf of St. Lawrence was later than normal in 2017 while at the Front it was earlier than usual, suggesting that some females from the Gulf herd moved to the Front due to the lack of ice suitable for pupping.
- The number of pups born in the traditional pupping area of the southern Gulf of St. Lawrence was greatly reduced, with an estimated pup production of only 18,300 (95% CI, 15,400-21,200 rounded to the nearest hundred). Another 13,600 (95% CI, 7,700-19,500) pups were born in the northern Gulf. An estimated 714,600 (95% CI, 538,800-890,400) pups were born off the northeastern coast of Newfoundland (Front); accounting for 96% of all pupping in 2017. Combining the estimates from all areas resulted in an estimated total pup production of 746,500 (95% CI, 570,300-922,700).
- The previous population model formulation did not fit the updated time series of pup production estimates and the reproductive rates as well as in previous assessments. To account for the effects of continued poor ice conditions and other environmental changes, the model was modified to allow juvenile mortality to vary. The impact of broader environmental variability on reproductive rates was also incorporated into the model using a large-scale environmental index.
- The model indicates that the population increased from the 1970s until the mid-1990s. Between the mid-1990s and 2011 the population was relatively stable. Since then it is estimated that the population has begun to increase likely due to reductions in the removals and high reproductive rates.
- The model estimated pup production in 2019 is 1.4 (95% CI, 1.23-1.49) million and a total population size of 7.6 (95% CI, 6.55-8.82) million.
- The Atlantic Seal Management Strategy identifies three reference levels based upon the maximum observed population, which is referred to as Nmax. Based upon the current model, Nmax was estimated to be 7.6 million, resulting in a Precautionary Reference Level N70 of 5.3 million animals and a Critical Reference Level, N30=2.3 million animals.
- Sustainable harvest levels that maintained an 80% probability of remaining above N70 for the next five years were estimated. The identified annual Canadian Total Allowable Catch (TAC) levels were 425,000, 375,000 and 175,000 animals assuming harvest age structures of 95%, 90% and 50% YOY, respectively.
- The estimated annual Potential Biological Removal (PBR) for the Northwest Atlantic population is 425,600.
- Both reproductive rates and, presumably, YOY mortality have been highly variable in recent years which has made it difficult to fit the model, suggesting that the effects of environmental variability on vital rates are not fully captured by the current model. This variability appears to have played a lesser role in the past.
- The expected decline in ice cover will lead to an increase in YOY mortality and changes in prey availability which influence reproductive rates. This will impact future advice on sustainable levels of harvest.
This Science Advisory Report is from the October 21-26, 2019 meeting of the National Marine Mammal Peer Review Committee. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.
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