Hooded seal (Cystophora cristata)
The stock of hooded seal has declined steadily after the last war, even after harvesting regulations were imposed in the 1960s. The West Ice stock has now been protected, there is a moratorium on harvesting, and the stock size has stabilized at a low level. The hooded seal is one of two pelagic seal species harvested in Norwegian waters.
What is being monitored?
Cite these dataInstitute of Marine Research (2019). Population size of hooded seals in the West Ice. Environmental monitoring of Svalbard and Jan Mayen (MOSJ). URL: http://www.mosj.no/en/fauna/marine/hooded-seal.html
|Modelled total stock size||Institute of Marine Research||1374700||1352100||1310300||1275800||1225300||1166500||1091400||1052200||1026500||969200||922200||888400||867000||807900||782300||752800||682700||635700||611400||581300||544690||510580||472280||459300||437140||402540||375040||356970||334350||310330||286080||278210||260380||243620||223530||212280||199090||183290||179990||175880||171420||165760||154960||146640||145670||143070||139060||128670||127040||120980||119230||117840||115130||110140||106790||105240||101960||96280||92700||89410||86820||84030||83870||83430||82550||81900||81470||81050||80600||80180||79750||79330||78910||78490||78080||77670||77260||76850||76440||76040||75640||75240||74840||74440|
|Modelled production of pups||Institute of Marine Research||230700||230100||227300||223800||219300||211200||198300||188000||181800||175000||168800||162200||155100||145500||140700||135900||125500||116400||110600||104600||98490||93780||85980||82000||77340||72140||67540||64170||60750||56130||51880||49010||45880||43720||41030||37180||33490||31290||29790||28280||28220||28260||27260||26240||25470||24470||23560||21670||21540||20580||20480||20460||20430||20230||19740||19150||18430||17830||17530||17000||16310||15530||15010||14610||14310||14220||14200||14130||14040||13960||13880||13810||13740||13660||13590||13520||13450||13380||13310||13240||13170||13100||13030||12960|
|Survey counts of pups||Institute of Marine Research||24000||15200||15370||13655|
High-resolution aerial photographs are used now. The number of first-year pups are counted on the photographs, and estimates of the number of pups produced, historical catch data and reproduction parameters are then used in a population model to calculate the total population size.
The uncertainty is mainly related to the sampling because it is impossible to photograph the entire breeding area; photographs are taken along transects.
Some uncertainty also relates to errors in reading the photographs, which are inspected manually. However, as the images are of such high quality, this uncertainty proves to be minimal compared with that related to sampling.
There is also some uncertainty connected with the need to photograph at the correct time. If photographs are taken too early, there is a risk of missing seals that have not yet been born, and if they are taken too late there is a risk that many seals have entered the water and are therefore not visible on the photographs. A great deal of effort has to be put into finding the correct time to take the photographs.
The estimates of the pup production also state the uncertainty of the estimate, which includes that attached to sampling, reading errors and the timing of the photography.
All estimates must be accounted for and approved by International Council for the Exploration of the Sea (ICES).
Reference level and action level
A management plan from ICES follows various reference values.
Status and trend
Consideration of all the models suggests that the hooded seal stock in the West Ice declined significantly between the end of the 1940s and around 1980, most probably due to high hunting pressure. It seems to have stabilized at a low level since then, at probably no more than 10–15 % of the level around 60 years ago.
Management of the species is based on estimates of pup production, derived from aerial surveys carried out in 1997, 2005, 2007 and 2012. Fertility data used in the model runs are from 1990–1994 and 2008–2010. After the aerial survey in 2012 the stock size was estimated to be 84,000 (95% CI: 68,000–100,000).
There are no comparable data on stock size and food availability that could enable an assessment of population dynamics in relation to food availability.
Since the hooded seal used to be hunted, the monitoring was originally largely aimed at providing a basis for setting hunting quotas.
In its long-term management strategy based on the precautionary principle, ICES has defined a lower limit for the population level that is 30% of the maximum known figure for the stock. It recommends that no form of hunting should be permitted when a stock is at or below that level.
Since the hooded seal stock in the West Ice is still below this level today, ICES advises that no hunting should take place.
Following the ICES recommendation, hunting was halted in 2007 except for a limited catch for research purposes.
About the monitoring
It is interesting to monitor the hooded seal because it is dependent upon ice and may be affected by climate change.
The management is based on estimates of the pup production made on the basis of aerial counts. This method has been chosen because it is simpler to count pups than adults in the quite short breeding season. Pups stay on the ice floes during surveys, while adults may disappear into the water. The methods to estimate the total stock size are thus indirect (model runs) and are also based on knowledge about the reproductive status of females derived from other types of survey.
Places and areas
Relations to other monitoring
- Monitoring programme
- International environmental agreements
- Voluntary international cooperation
- Related monitoring