Hooded seal
Last updated 12 May 2020
The hooded seal (Cystophora cristata) is one of two pelagic seal species that have been harvested in Norwegian territories. The population size of hooded seal has declined steadily after the last war, even after harvesting regulations were imposed in the 1960s. The species has now been protected, and the population size has stabilized at a low level.
What is being monitored?
Population size in West Ice
Far too many hooded seals were harvested in the West Ice in the first two decades after the Second World War. The stock therefore declined up to the end of the 1960s, when hunting regulations were introduced. Despite these, the decline continued until around 1980. After that, it seems to have stabilized at a low level (estimated to approximately 77 000 seals in 2019), which is probably less than 10% of the level 70 years ago. The population was therefore protected in 2007. The blue line shows the modelled total stock, the black line the modelled pup production and green dots show the estimated pup production based on aerial censuses.
(Cite these data: Institute of Marine Research (2022). Population size of hooded seals in the West Ice. Environmental monitoring of Svalbard and Jan Mayen (MOSJ). URL: https://mosj.no/en/fauna/marine/hooded-seal.html)
Details on these data
| Last updated | 12 May 2020 |
| Update interval | Stock size: annually Estimates of pup production: Every 3–5 years |
| Next update | November 2023 |
| Commissioning organization | Ministry of Trade, Industry and Fisheries |
| Executive organization | Institute of Marine Research |
| Contact persons | Martin Biuw |
Method
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.
Quality
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, 2012, and 2018. Fertility data used in the model runs are from 1990–1994 and 2008–2010. After the aerial survey in 2018 the population size was estimated to be 77 300 (95% CI: 60 100 – 94 600).
This means that the protection from 2007 has failed to manifest as a measurable increase in population size up till present, which most likely means that there are other environmental factors that limit population growth. There are however no comparable data on population size and food availability that could enable an assessment of population dynamics in relation to food availability.
Causal factors
Since the hooded seal used to be hunted, the monitoring was originally largely aimed at providing a basis for setting hunting quotas.
Consequences
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 (while breeding and moulting) and may be affected by climate change. It is also a significant predator in the Norwegian Sea and the sea ice zone.
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
- None
International environmental agreements
- None
Voluntary international cooperation
- None
Related monitoring
- None
Further reading
Links
- ICES Working Group on Harp and Hooded Seals (WGHARP)
Working group within the International Council for the Exploration of the Sea (ICES), that carries out analyses and prepares the scientific basis for ICES advice on hooded seals. - Institute of Marine Research – hooded seal
Publications
- ICES (ed.). 2014. Report of the ICES/NAFO Working Group on Harp and Hooded Seals (WGHARP). Quebec, Canada: International Council for the Exploration of the Sea. 62 pp.
- ICES/NAFO, (ed.). 2019. Report of the Joint ICES/NAFO/NAMMCO Working Group on Harp and Hooded Seals (WGHARP), 2-6 Sept. 2019, Tromsø, Norway. ICES Scientific Reports 1(72). 193 pp.
DOI:10.17895/ices.pub.5617 - Salberg, A.-B., Haug, T., Nilssen, K.T. 2008. Estimation of hooded seal (Cystophora cristata) pup production in the Greenland Sea pack ice during the 2005 whelping season. Polar biol 31: 867–878.
DOI:10.1007/s00300-008-0425-0 - Øigård, T.A., Haug, T., Nilssen, K.T. 2014. Current status of hooded seals in the Greenland Sea. Victims of climate change and predation? Institute of Marine Research 172: 29–36.
DOI:10.1016/j.biocon.2014.02.007
