Harp seal

Last updated 12 May 2020

Harp seals (Pagophilus groenlandicus) are monitored because the population can be affected by hunting and the species is dependent upon ice and may be affected by climate change. It is also one of the most numerous and important top predators in the Norwegian Sea and the Barents Sea. There is still a harp seal hunt in both the West Ice and the East Ice. Population monitoring revealed that the annual production of pups in the East Ice decreased significantly in the mid-2000s, after which it seems to have stabilized on a lower level. Pup production in the West Ice have been stable up till 2018, when a new survey revealed a decrease here as well.

Status and trend

The harp seals in the northeastern Atlantic Ocean are regarded as distinct from the Canadian harp seals. The pups are born in March-April on the pack ice in 2 well-demarcated areas:

1. Between Jan Mayen and the east coast of Greenland (the West Ice)
2. In the southeastern Barents Sea and the White Sea (the East Ice)

Harp seals are pelagic outside the pupping season, mainly in areas with pack ice. Long foraging migrations are undertaken, mainly to the northern part of the Barents Sea. Therefore, seals from both the West Ice and the East Ice are found in the Svalbard area in summer and autumn.

The main message from this monitoring is that the population in the East Ice has decreased since the mid-2000s. The population in the West Ice appeared for a long time to be stable or somewhat increasing, however, at the latest count in 2018 it was observed a reduction in pup production of almost 40%.

The West Ice

When the West Ice stock was modelled in 2019, estimates were used for pup production from tagging and recovery trials undertaken during 1983–1991 and aerial censuses from 2002, 2007, 2012, and 2018. Modelling based on these figures gave an estimated production of 66 407 pups (95% confidence interval 51 600–81 209) and a stock of 360 400 seals over one year old (1+) (95% confidence interval 258 240–463 555) in 2019. This gives a total stock of around 430 000 individuals (95% confidence interval 310 000–540 000).

Based on the uncertainty linked to a decrease in the pup production, ICES has recommended that the harvest level is based on the most conservative estimate (Potential Biological Removal), which gives a recommended harvest quota of 11 548 animals (regardless of age).

The East Ice

In the East Ice, Russian aerial censuses that were performed in the White Sea in 1998, 2000 (two independent censuses), 2002, 2003, 2004, 2005, 2008, 2009, 2010 and 2012 gave 11 independent estimates for pup production in this harp seal stock.

The estimates from 2005 and 2008 are uncertain, particularly because the censuses were performed so late in the season. This may have helped to produce the very low figures.

The estimates from 2004, 2009, 2010 and 2013, however, indicate a substantial reduction in the pup production in this stock. So far, there is no satisfactory explanation for this, but the fertility of the females seems likely to have been reduced, most likely caused by reduced prey availability. Difficult ice conditions in the White Sea since 2003 may also have contributed to the reduction. Perhaps part of the stock has moved to new, so far unknown, pupping sites beyond the White Sea.

There are no new estimates of pup production available after 2013, although data on reproduction were collected in 2018. Modelling using these input data gave an estimated production of 220 300 pups (95% confidence interval 191 200 – 249 400) and a stock of 1 276 900 animals over one year old (1+) (95% confidence interval 1 100 300 – 1 453 500) in 2019. This gives a total stock of around 1 497 200 individuals (95% confidence interval 1 293 000 – 1 701 400).

Based on the uncertainty linked to a decrease in the pup production since 2013, ICES has recommended that the harvest level is based on the most conservative estimate (Potential Biological Removal), which gives a recommended harvest quota of 21 172 animals (regardless of age).

Causal factors

Catch quotas are set every other year based on calculations of the total stock and what are referred to as sustainable catches, which is the catch volume that we can assume will stabilize the stock. Due to uncertainties in the development of both populations, quotas have been set by using the so-called Potential Biological Removal (PBR) method, which is a more conservative methods than those traditionally used.

The ICES Advisory Committee for Fishery Management (ACOM) regards the catch in both the West Ice and the East Ice as being within safe biological limits. There are no comparable data for the stock size and access to food to permit a discussion of such relationships.

Consequences

The harp seals in the East Ice and the West Ice were far too heavily harvested during the first two decades after the Second World War. The stocks therefore declined in size right up to the end of the 1960s, when regulation of the hunting was introduced. This, combined with a declining hunting effort during the 1970s, had a positive effect on both stocks, which immediately began to grow.

Pup production in the East Ice decreased significantly after 2003, and it now looks as if the population in the West Ice shows similar tendencies. There have been no surveys in the East Ice since 2013. ICES recommends that surveys should be conducted every 5 years in order for a population to be considered data rich.

The total consumption by the seal population can be calculated based on knowledge of feeding habits (acquired on special cruises and from catches) and the size and demography of the population. It has been calculated that, in the course of one year, the East Ice stock consumes about 3.5 million tons of various prey in the Barents Sea.

About the monitoring

Harp seals are monitored because the population can be affected by hunting and the species is dependent upon ice and may be affected by climate change. The species is also one of the most numerous and most important top predators in the Norwegian Sea and the Barents Sea. Commercial catching of harp seals takes place in the East ice (Norway and Russia) and the West Ice (Norway). The population monitoring has largely had the objective of providing a basis to set hunting quotas.

The most important basis for the recommendations has been estimates of the pup production, based on counts and tagging and recovery experiments. This approach is chosen as it is easier to count pups during the limited breeding season than to count adult seals. Pups remain on the ice during counting, but adults may enter the sea. Hence, methods to calculate total populations are indirect (model calculations) based on supplementary knowledge from other studies on reproductive status with the females.

In addition to being a harvesting resource, the harp seal is abundant and is able to consume large quantities of fish from the fish stocks in the Greenland Sea, the Barents Sea and the waters surrounding Svalbard. Hence, its feeding behaviour and fish consumption is being monitored, to estimate its influence when estimating fish mortality in important fish stocks (e.g. capelin). Knowledge of the size and demography of the population is needed to calculate its total consumption of fish.

Further reading