CASPIAN SEAL

 

A Caspian Seal In Iran

The Caspian seal (Pusa caspica, syn. Phoca caspica) is one of the smallest members of the earless seal family and unique in that it is found exclusively in the brackish Caspian Sea. It lives along the shorelines, but also on the many rocky islands and floating blocks of ice that dot the Caspian Sea. In winter and cooler parts of the spring and autumn season, it populates the northern Caspian coastline. As the ice melts in the summer and warmer parts of the spring and autumn season, it also occurs in the deltas of the Volga and Ural Rivers, as well as the southern latitudes of the Caspian where the water is cooler due to greater depth.

Evidence suggests that the colonization events of Caspian seals were probably facilitated by river connections from the Arctic that have since disappeared, land locking the populations sometime before the major Pleistocene glaciations.

Distinctive characteristics

Caspian seals are medium gray to grayish brown above and paler below in a typical countershaded pattern. There are often yellowish undertones to the coat color. Caspian seals have a highly variable light covering of irregular light-colored spots on their darker areas and dark spots on lighter areas. Males are typically more heavily spotted than females. Caspian seals do not have the rings typical of ringed seals. The head and nape can be darker than the rest of the upper body and can be a rusty shade in some animals. Pups are born in a long white lanugo coat that is molted around weaning, at three weeks to a month. The juvenile coat is a darker gray version of the adult pelage.

Caspian seals are relatively short and plump. The head is small in proportion to the body with large conspicuous narrow set eyes. The muzzle has a wide and somewhat flattened appearance, with conspicuous whitish vibrissae.

Dental formula    I 3/2, R 1/1, PC 6/5.

Size

Adult males and females reach maximum lengths of 1.5 and 1.4 m, respectively, and weigh around 86 kg. Pups are 64-79 cm and about 5 kg at birth.

Life Span

Range life Span 26 -50 years; Average life Span 35 years.

Gestation Period    304-334 days.

Can be confused with

No other pinniped occurs in the Caspian Sea, and this species occurs nowhere else in the world.

Distribution

Caspian seals are entirely confined to the saline waters of the Caspian Sea and its feeder rivers. Seasonal movements in the Caspian seal are prompted by ice formation. Seals occupy the north eastern quadrant of the sea in autumn, and except for molting aggregations that occur in this area in the spring, their movements and distribution in ice free times of the year are poorly known.

Ecology and behavior

The origin of the Caspian seal is uncertain, but they are closely related to ringed and Baikal seals. Pups are born on ice floes amongst the rough mounded ice formations of the northern reaches of the Caspian Sea from late winter to spring. Females typically keep their pups by holes they maintain in the ice away from the edges of floes. Pups are weaned in 3-4 weeks, and females mate around this time. Molting follows breeding and the timing is staggered, depending on sex and age class. Adult females that have bred, molt first, and adult males molt last, finishing by early May with the rest of the population beginning and finishing between these two classes.

Predation

Besides human, the two other predators of Caspian seals are sea eagles (Haliaeetus leucoryphus) and wolves (Canis lupus). Sea eagles snatch up new born pups soon after they are born, during lactation their mortality rate is around 22%. In the northern part of the Caspian Sea, wolves will kill seals lying out on islands.

Feeding and prey

Caspian seals take a wide variety of fishes and small crustaceans; the diet varies seasonally. Dive data from two adult males revealed that most dives lasted less than 50 seconds, with some dives extending to over 3 minutes. Depths were typically less than 50 m with a few dives reaching over 200 m.

Exploitation

The seal population of the Caspian has been exploited commercially for over a century. Tens of thousands were harvested each year and “for some years in the mid-20th century the numbers were in the 100s of thousands” (CISS). Other important threats to the Caspian seal include deliberate killing by fishermen around fishing operations, and accidental drowning (by-catch) in fishing nets, disease, organochlorine contamination of the food chain (particularly from DDT) can cause infertility in older females, disruption of the Caspian Sea food chain causing reduced prey availability for the Caspian for seals due to overfishing and invasion by the comb jelly Mnemiopsis leidyi, and loss of habitat. In the future climate change may also become important issue if this leads to reduction or instability of the winter ice fields used for breeding.

Threats and status

Subsistence, commercial hunting, and poaching continue to this day. The population probably exceeded one million animals early in the 20th century, and was estimated at 360,000-400,000 in the late 1980s. There have been several large mortality events attributed to canine distemper virus (morbillivirus) outbreaks beginning in the late 1990s and extending to 2001. Variability in the period and extent of ice cover attributed to global warming may be playing a role in these outbreaks by forcing seals to concentrate on haul-out sites to molt as opposed to being more dispersed on both ice and land haul-outs. Survival of pups may also be affected if ice cover continues to decrease. There has been considerable industrial development in and around the shores of the Caspian Sea, and discharge of high levels of many kinds of pollutants from the 20th century to the present time. Exposure to, and accumulation of, a variety of these contaminants in Caspian seals has been reported to play a role in weakening the immune systems of these animals and contributing to the disease outbreaks. Overfishing in this large, but essentially closed, ecosystem is an ongoing concern.

Factors hypothesized include

The direct and indirect effects of large-scale commercial fisheries on key prey species, long –term ecosystem shifts, and changes in behavior by a primary predator, the killer whale, or a combination of these factors.

IUCN status    Endangered

Two White Coat Pups (foreground) On Island Sandy Beach