Hooded seal

The hooded seal mother only lactate for about 4 days. The mating takes place just after she abandon the pup and a male hooded seal will often wait next to the mother and pup. He will often get challenged by other rivals.
The hooded seal mother only lactate for about 4 days. The mating takes place just after she abandon the pup and a male hooded seal will often wait next to the mother and pup. He will often get challenged by other rivals.

Cystophora cristata

Size

The hooded seal is a large seal. Fully grown females measure approx. 2 metres, while fully grown males on average reach up to around 2.60 metres. Males grow to be significantly heavier and more powerfully built than females. The hooded seal is thinnest immediately after moulting in July. At that point, a fully grown female will weigh between 150-200kg, while fully grown males weigh 250-300kg. During the winter, their weight will be up to 50% higher than their summer weight, so females will weigh up to 300kg and males can reach about 450kg.

Food

The hooded seal consumes a large part of its food in the areas of open water and precisely what it eats out there is not known. But in the coastal areas, hooded seal often eat large fish, for example Greenland halibut, redfish and cod, as well as squid. Studies of hooded seals' fatty acid composition show that Atlantic argentine (Argentina silus), a large shoal fish living in deep water in most of the hooded seals distribution area, is also an important food item.

Reproduction

As with the other Greenland seal species, hooded seals usually become sexually mature around the age of five (some a year or two earlier or later). During the winter, the adult hooded seals gather in specific areas where they give birth to their pups (see Distribution and numbers). Most hooded seals are born in the latter half of March, but births can occur from early March to early April. Pups are about 1 metre long at birth and weigh 23-30kg. The suckling period is only about 4 days, during which short time the pups take on no less than 7kg a day. Mating takes place when the pup is finished suckling, after which the pup is left to fend for itself. After mating, the fertilized egg divides itself a few times and becomes dormant. The egg does not attach itself to the womb (implantation) before late July or early August and then embryonic development begins.

During the first weeks, the pup stays near the ice where it was born. Here it quickly improves in swimming and diving, and then suddenly begins on a long swim, which brings it in an almost straight line over to the field ice off East Greenland, where it will grow into an adult. Some hooded seals are though also caught along the west coast of Greenland from Upernavik and south. Whether they are pups from Newfoundland which have swum in a slightly wrong direction, or if they are pups from the breeding grounds in the Davis Strait, we do not know yet.

Moulting

Hooded seals gather in June-July in order to moult (shed hair). Hooded seals which breed off the coast of North-east Greenland also moult off North-east Greenland, while West Atlantic hooded seal gather in the field ice near Ammassalik to moult.

Distribution and numbers

Distribution and numbers

The figure shows the main distribution and features of hooded seal migration, along with an estimate, i.e. a calculated figure, of the number of seals divided by breeding areas. The numbers for the West Atlantic population are from 2005 and the number of the East Atlantic population is from 2013. The seals at the three fields west of Greenland interchange, so the number of seals in the three fields can vary. In particular, the number of seals that breed in the Davis Strait off Nuuk varies widely from year to year. In 1984, the researchers calculated a figure of 18,600 pups born in this area, but in 2005 the estimate was of only around 3,350 pups. The number of current year pups is usually about 1/5th of the total population.

Status

Pup of the year (Blueback). Photo: Aqqalu Rosing-Asvid
Pup of the year (Blueback). Photo: Aqqalu Rosing-Asvid

It is believed that the commercial catch around Newfoundland earlier reduced the population considerably. In 1918, the last great catch of more than 20,000 hooded seals was landed and, since then, catches have been relatively modest, probably because the population has been kept at a low level. In the early 1980s, various management measures were put into place that reduced the commercial catch. Since 1993, there has been a ban in Canada on the commercial use of skin from hooded seals (bluebacks), and Canadian catches in the last decade have been modest, i.e. a few hundred. The Greenland catch has in recent years been between 4,000 and 6,000. The total catch is thus about 1% of the stock, and with this relatively modest catch, one must assume that this population of hooded seal will increase in numbers.

The hooded seal population off the coast of North-east Greenland was also greatly reduced by large commercial catches in the years after World War II. Researchers' calculations suggest that the current population is only around 10% of levels before commercial hunting began. Commercial catch was therefore stopped in 2007 and replaced by a scientific catch of a few hundred seals. In addition, hunters from Ittoqortoormiit take a smaller number of around 20 hooded seals annually.  With such a small catch, the population should be growing again, but the most recent survey have not detected any growth so far. In Greenland's Red List, the hooded seal is categorized as not threatened.

Management

Hooded seals are monitored by an international working group under ICES, which advises administrators on quotas for the commercial catch. The working group consists of researchers from Norway, Canada, Greenland and Russia. Populations are monitored by scientists using flight surveys to count and calculate the number of pups produced. The total number of seals in the population is calculated from this pup estimate, along with data about the age composition of the population, age of sexual maturity and the proportion of adult females that give birth to a pup.

Research

Tracking of West Atlantic hooded seals. The figure shows the tracking of 29 adult hooded seals from the breeding areas near Canada to the molting area near Tasiilaq (April-June, green lines) and 21 year cycles of adult hooded seals from the molting area and back to the molting area (July-June, red lines). (Sources DFO, Canada and the Greenland Institute of Natural Resources / Map by Julie Andersen).

In 2004-7, the Greenland Institute of Natural Resources in cooperation with Canadian scientists and hunters from the Ammassalik area put data loggers on hooded seals. The hooded seals had just completed their moulting at the moulting grounds off Ammassalik. The data loggers were glued onto the new coat and sent data via satellite on the hooded seals' location and diving behaviour. This study shows that the adult hooded seals from the western Atlantic population follow a relatively uniform annual cycle (see figure with migratory paths). They eat and search for food mostly in open water. The deepest dive registrated was 1652m and the seal was down for an hour. Besides presenting the migration and dive patterns, the transmitters were simultaneously used to collect data on ocean temperature and salinity down through the water column in the waters off South-east Greenland.

Updated 01.16.2017