Hooded seal
Hooded seal[1] | |
---|---|
Specimen at Museum Koenig | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Carnivora |
Clade: | Pinnipedia |
Family: | Phocidae |
Subfamily: | Phocinae |
Genus: | Cystophora Nilsson, 1820 |
Species: | C. cristata
|
Binomial name | |
Cystophora cristata (Erxleben, 1777)
| |
Distribution of the hooded seal. Breeding grounds indicated in blue. |
The hooded seal (Cystophora cristata) is a large
Naming
The generic name Cystophora means "bladder-bearer" in Greek, from the species' unusual sexual ornament – a peculiar inflatable bladder septum on the head of the adult male. This bladder hangs between the eyes and down over the upper lip in the deflated state. In addition, the hooded seal can inflate a large balloon-like sac from one of its nostrils. This is done by shutting one nostril valve and inflating a membrane, which then protrudes from the other nostril.[5]
Size
Adult males are 2.6 meters (8 ft 6 in) long on average, can grow to 3.5 m, and weigh 300–410 kg (660–900 lb). Sexual dimorphism is obvious from birth and females are much smaller: 2.03 meters (6 ft 8 in) long and weighing 145–300 kg (320–661 lb).[6][7] The color is silvery; the body is scattered with dark, irregular marks. The head is darker than the rest of the body, and without marks.
Distribution and habitat
Hooded seals live primarily on drifting pack ice and in deep water in the Arctic Ocean and North Atlantic. Although some drift away to warmer regions during the year, their best survival rate is in colder climates. They can be found on four distinct areas with pack ice: near
Diet
The diet of the hooded seal is composed primarily of various amphipods (crustaceans), euphausiids (krill), and fish, including Atlantic argentine, capelin, Greenland halibut, cod, herring, and redfish.[4][11] They also are known to eat squid, sea stars, and mussels.[4] Relative to the other species, hooded seals consume 3 times the proportion of redfish; percentages of capelin were similar in relation to closely related species.[11] Capelin is considered a more common choice of sustenance during the winter season. Their diet is considered to be rich in lipids and fatty acids.[12]
Behavior
Hooded seals tend to feed in relatively deep waters ranging from 100–600 m (330–1,970 ft), and dive from 5 to 25 minute durations. However, some dives can go deeper than 1,016 m (3,333 ft) and as long, or longer, than 52 minutes. Diving is rather continuous, with approximately 90% of their time spent submerged during the day and night, although dives during the day are generally deeper and longer. Dives during the winter are also deeper and longer than those in the summer. It is known that the hooded seal is generally a solitary species, except during breeding and molting seasons. During these two periods, they tend to fast as well. The seals mass annually near the Denmark strait around July, at the time of their molting periods, to mate.[13][14] Hooded seals are a relatively unsocial species compared to other seals, and they are typically more aggressive and territorial. They demonstrate aggression by inflating the "hood" (which is explained in the "Nasal Cavity" section below). They frequently migrate and remain alone for most of the year, except during mating season.[4][6]
Nasal cavity
The hooded seal is known for its uniquely elastic nasal cavity located at the top of its head, also known as the hood.[4] Only males possess this nasal sac, which they begin to develop around the age of four.[15] The hood begins to inflate as the seal makes its initial breath prior to going underwater. It then begins to repetitively deflate and inflate as the seal is swimming. The purpose of this happening is for acoustic signaling, meaning that it occurs when the seal feels threatened and attempts to ward off hostile species when competing for resources such as food and shelter.[16] It also serves to communicate their health and superior status to both other males and females they are attempting to attract.[15] In sexually mature males, a pinkish balloon-like nasal membrane comes out of the left nostril to further aid it in attracting a mate. This membrane, when shaken, is able to produce various sounds and calls depending on whether the seal is underwater or on land. Most of these acoustic signals are used in acoustic situation (about 79%), while about 12% of the signals are used for sexual purposes.[17]
Breeding and life cycle
There are four major breeding areas for the hooded seal: the Gulf of St. Lawrence; the "Front" east of Newfoundland; Davis Strait (between Greenland and northern Canada); and the West Ice near Jan Mayen. Male hooded seals are known to have several mates in a single mating season, following the hypothesis that they are polygynous. While some males will defend and mate with just one female for long periods of time, others will be more mobile and tend to mate with multiple females for shorter periods of time, generating maximum offspring within the population.[18] Most males reach sexual maturity by 5 years of age.[19]
Throughout all areas, the hooded seals
Offspring
Pups are about 1 metre (3 ft 3 in) long at birth and weigh about 24 kilograms (53 lb). They are born on the ice from mid-March to early April with a well-developed blubber layer and having shed their pre-natal coat. They are born with a slate blue-grey coat (giving them the name "blueback"), with a pale cream color on the belly, which they will molt after about 14 months. Nursing of the pup lasts for an average of only 4 days, the shortest lactation period of any mammal, during which the pup doubles in size, gaining around 7 kilograms (15 lb)/day. This is possible because the milk that they drink has a fat content of 60%.[23] The female pup will mature between ages 3 and 6, whereas the male pup will mature between ages 5 and 7.
Early development
Researchers find that due to a pup's differing needs in regards to sustaining work and foraging while under water compared to adults, the skeletal and cardiac muscles develop differently. Studies show that cardiac blood flow provides sufficient
Hooded seals shed their lanugo fur in the womb and are born with a thin non lanugo fur coat, which is a less efficient thermoregulating fur coat compared to some to other seal species (e.g., leopard seals).[26] Studies have shown that newborn hooded seals undergo a stage after birth where the thickness of their blubber grows rapidly, which maximizes their ability to thermoregulate and compensate for their thin fur coat.[27] This process of fur removal in the womb and alternatively using blubber may be advantageous because water cannot penetrate blubber like it does with fur, therefore blubber can insulate the seals in both water and air fairly uniformly.[27]
Lifespan
The hooded seal can live to about age 30 to 35.[6]
Threats and conservation practices
Prior to the 1940s, adult hooded seals were primarily hunted for their leather and oil deposits. More recently, the main threats are hunting, including subsistence hunting, and bycatch. Seal strandings are not considered a large threat to hooded seal populations but are highly researched. Seal pups are hunted for their blue and black pelts and many mothers are killed in the process, attempting to protect their young. Hunting primarily occurs in areas of Greenland, Canada, Russia, and Norway.[4] Overall, northwest Atlantic hooded seal populations are stable or increasing whereas the northeast Atlantic populations have declined by 85–90% within the last 60 years.[2]
It was believed by the scientific community that sonar was leading to mass stranding of hooded seals. After multiple sonar tests on captive seals, ranging from 1 to 7 kHz, it became evident that it had little effect on the subjects. The first test on each subject yielded differing results, ranging from reduced diving activity and rapid exploratory swimming. A difference was only noted for all subjects on their initial exposure.[26]
Conservation practices, brought about by international cooperation and the formation of the Northwest Atlantic Fisheries Organization (NAFO) led to hooded seal population increases. It is now required to hold a license to hunt hooded seals in international waters and each license is set a quota. Total allowable catch of hooded seals are set at 10,000 annually.[4]
The hooded seal is protected under the
-
Mother with pup.
See also
References
- OCLC 62265494.
- ^ . Retrieved 19 November 2021.
- ^ Kovacs, Kit. "Hooded Seal". Noerwegian Polar Institute.
- ^ a b c d e f g h "Hooded Seal (Cystophora cristata)". National Marine Fisheries Service. 5 October 2022.
- ^ Hooded Seal (Cystophora cristata), a Weird Animal Archived 2010-12-29 at the Wayback Machine. Drawfluffy.com. Retrieved on 2011-09-16.
- ^ a b c d e "Hooded Seals, Cystophora cristata". Marinebio. Archived from the original on 6 March 2012. Retrieved 24 October 2013.
- ^ Hooded seal images Archived 2011-08-30 at the Wayback Machine. arkive.org
- .
- ^ S2CID 85897546.
- .
- ^ .
- .
- S2CID 13600793.
- ^ "Cystophora cristata Hooded Seal". Animal Diversity Web. Retrieved 24 October 2013.
- ^ a b Witmer, Lawrence (2001). "A nose for all reasons". Natural History. 110 (5): 65.
- ^ Frank, RJ.; Ronald, K. (1982). "Some underwater observations of hooded seal, Cystophora cristata (Erxleben), behaviour". Aquatic Mammals. 9 (2): 67–68.
- doi:10.1139/z95-159.
- doi:10.1139/z90-349.
- ^ Miller, Edward H., Ian L. Jones, and Garry B. Stenson. "Baculum and testes of the hooded seal (Cystophora cristata): growth and size-scaling and their relationships to sexual selection." Canadian Journal of zoology 77.3 (1999): 470-479.
- .
- doi:10.1139/f87-037. Archived from the original(PDF) on 2016-03-04. Retrieved 2015-08-28.
- S2CID 24159024.
- S2CID 8382913.
- ^ PMID 20154189.
- PMID 23348948.
- ^ doi:10.1578/AM.36.3.2010.239. Archived from the original(PDF) on 2016-03-04. Retrieved 2015-09-04.
- ^ PMID 25151642.
- ^ "Marine Mammal Protection Act". NOAA Fisheries. NOAA. Retrieved 25 October 2013.